/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.lang3.reflect;

import java.lang.annotation.Annotation;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.apache.commons.lang3.ArrayUtils;
import org.apache.commons.lang3.ClassUtils;
import org.apache.commons.lang3.JavaVersion;
import org.apache.commons.lang3.StringUtils;
import org.apache.commons.lang3.SystemUtils;
import org.apache.commons.lang3.Validate;

Utilities for working with Fields by reflection. Adapted and refactored from the dormant [reflect] Commons sandbox component. 

The ability is provided to break the scoping restrictions coded by the programmer. This can allow fields to be
changed that shouldn't be. This facility should be used with care.
Since:
2.5/**
 * Utilities for working with {@link Field}s by reflection. Adapted and refactored from the dormant [reflect] Commons
 * sandbox component.
 * <p>
 * The ability is provided to break the scoping restrictions coded by the programmer. This can allow fields to be
 * changed that shouldn't be. This facility should be used with care.
 *
 * @since 2.5
 */
public class FieldUtils {

    
FieldUtils instances should NOT be constructed in standard programming. 
 This constructor is public to permit tools that require a JavaBean instance to operate. 
/**
     * {@link FieldUtils} instances should NOT be constructed in standard programming.
     * <p>
     * This constructor is {@code public} to permit tools that require a JavaBean instance to operate.
     * </p>
     */
    public FieldUtils() {
        super();
    }

    
Gets an accessible Field by name respecting scope. Superclasses/interfaces will be considered. 
Params:
cls –  the Class to reflect, must not be null
fieldName – 
           the field name to obtain
Throws:
IllegalArgumentException –  if the class is null, or the field name is blank or empty
Returns:
the Field object/**
     * Gets an accessible {@link Field} by name respecting scope. Superclasses/interfaces will be considered.
     *
     * @param cls
     *            the {@link Class} to reflect, must not be {@code null}
     * @param fieldName
     *            the field name to obtain
     * @return the Field object
     * @throws IllegalArgumentException
     *             if the class is {@code null}, or the field name is blank or empty
     */
    public static Field getField(final Class<?> cls, final String fieldName) {
        final Field field = getField(cls, fieldName, false);
        MemberUtils.setAccessibleWorkaround(field);
        return field;
    }

    
Gets an accessible Field by name, breaking scope if requested. Superclasses/interfaces will be considered. 
Params:
cls –  the Class to reflect, must not be null
fieldName – 
           the field name to obtain
forceAccess –  whether to break scope restrictions using the AccessibleObject.setAccessible(boolean) method. false will only match public fields.
Throws:
NullPointerException – if the class is null
IllegalArgumentException – if the field name is blank or empty or is matched at multiple places
in the inheritance hierarchy
Returns:
the Field object/**
     * Gets an accessible {@link Field} by name, breaking scope if requested. Superclasses/interfaces will be
     * considered.
     *
     * @param cls
     *            the {@link Class} to reflect, must not be {@code null}
     * @param fieldName
     *            the field name to obtain
     * @param forceAccess
     *            whether to break scope restrictions using the
     *            {@link java.lang.reflect.AccessibleObject#setAccessible(boolean)} method. {@code false} will only
     *            match {@code public} fields.
     * @return the Field object
     * @throws NullPointerException if the class is {@code null}
     * @throws IllegalArgumentException if the field name is blank or empty or is matched at multiple places
     * in the inheritance hierarchy
     */
    public static Field getField(final Class<?> cls, final String fieldName, final boolean forceAccess) {
        Validate.notNull(cls, "The class must not be null");
        Validate.isTrue(StringUtils.isNotBlank(fieldName), "The field name must not be blank/empty");
        // FIXME is this workaround still needed? lang requires Java 6
        // Sun Java 1.3 has a bugged implementation of getField hence we write the
        // code ourselves

        // getField() will return the Field object with the declaring class
        // set correctly to the class that declares the field. Thus requesting the
        // field on a subclass will return the field from the superclass.
        //
        // priority order for lookup:
        // searchclass private/protected/package/public
        // superclass protected/package/public
        // private/different package blocks access to further superclasses
        // implementedinterface public

        // check up the superclass hierarchy
        for (Class<?> acls = cls; acls != null; acls = acls.getSuperclass()) {
            try {
                final Field field = acls.getDeclaredField(fieldName);
                // getDeclaredField checks for non-public scopes as well
                // and it returns accurate results
                if (!Modifier.isPublic(field.getModifiers())) {
                    if (forceAccess) {
                        field.setAccessible(true);
                    } else {
                        continue;
                    }
                }
                return field;
            } catch (final NoSuchFieldException ex) { // NOPMD
                // ignore
            }
        }
        // check the public interface case. This must be manually searched for
        // incase there is a public supersuperclass field hidden by a private/package
        // superclass field.
        Field match = null;
        for (final Class<?> class1 : ClassUtils.getAllInterfaces(cls)) {
            try {
                final Field test = class1.getField(fieldName);
                Validate.isTrue(match == null, "Reference to field %s is ambiguous relative to %s"
                        + "; a matching field exists on two or more implemented interfaces.", fieldName, cls);
                match = test;
            } catch (final NoSuchFieldException ex) { // NOPMD
                // ignore
            }
        }
        return match;
    }

    
Gets an accessible Field by name respecting scope. Only the specified class will be considered. 
Params:
cls –  the Class to reflect, must not be null
fieldName – 
           the field name to obtain
Throws:
IllegalArgumentException –  if the class is null, or the field name is blank or empty
Returns:
the Field object/**
     * Gets an accessible {@link Field} by name respecting scope. Only the specified class will be considered.
     *
     * @param cls
     *            the {@link Class} to reflect, must not be {@code null}
     * @param fieldName
     *            the field name to obtain
     * @return the Field object
     * @throws IllegalArgumentException
     *             if the class is {@code null}, or the field name is blank or empty
     */
    public static Field getDeclaredField(final Class<?> cls, final String fieldName) {
        return getDeclaredField(cls, fieldName, false);
    }

    
Gets an accessible Field by name, breaking scope if requested. Only the specified class will be considered. 
Params:
cls –  the Class to reflect, must not be null
fieldName – 
           the field name to obtain
forceAccess –  whether to break scope restrictions using the AccessibleObject.setAccessible(boolean) method. false will only match public fields.
Throws:
IllegalArgumentException –  if the class is null, or the field name is blank or empty
Returns:
the Field object/**
     * Gets an accessible {@link Field} by name, breaking scope if requested. Only the specified class will be
     * considered.
     *
     * @param cls
     *            the {@link Class} to reflect, must not be {@code null}
     * @param fieldName
     *            the field name to obtain
     * @param forceAccess
     *            whether to break scope restrictions using the
     *            {@link java.lang.reflect.AccessibleObject#setAccessible(boolean)} method. {@code false} will only
     *            match {@code public} fields.
     * @return the Field object
     * @throws IllegalArgumentException
     *             if the class is {@code null}, or the field name is blank or empty
     */
    public static Field getDeclaredField(final Class<?> cls, final String fieldName, final boolean forceAccess) {
        Validate.notNull(cls, "The class must not be null");
        Validate.isTrue(StringUtils.isNotBlank(fieldName), "The field name must not be blank/empty");
        try {
            // only consider the specified class by using getDeclaredField()
            final Field field = cls.getDeclaredField(fieldName);
            if (!MemberUtils.isAccessible(field)) {
                if (forceAccess) {
                    field.setAccessible(true);
                } else {
                    return null;
                }
            }
            return field;
        } catch (final NoSuchFieldException e) { // NOPMD
            // ignore
        }
        return null;
    }

    
Gets all fields of the given class and its parents (if any).
Params:
cls –  the Class to query
Throws:
IllegalArgumentException –  if the class is null
Returns:
an array of Fields (possibly empty).
Since:
3.2/**
     * Gets all fields of the given class and its parents (if any).
     *
     * @param cls
     *            the {@link Class} to query
     * @return an array of Fields (possibly empty).
     * @throws IllegalArgumentException
     *             if the class is {@code null}
     * @since 3.2
     */
    public static Field[] getAllFields(final Class<?> cls) {
        final List<Field> allFieldsList = getAllFieldsList(cls);
        return allFieldsList.toArray(ArrayUtils.EMPTY_FIELD_ARRAY);
    }

    
Gets all fields of the given class and its parents (if any).
Params:
cls –  the Class to query
Throws:
IllegalArgumentException –  if the class is null
Returns:
an array of Fields (possibly empty).
Since:
3.2/**
     * Gets all fields of the given class and its parents (if any).
     *
     * @param cls
     *            the {@link Class} to query
     * @return an array of Fields (possibly empty).
     * @throws IllegalArgumentException
     *             if the class is {@code null}
     * @since 3.2
     */
    public static List<Field> getAllFieldsList(final Class<?> cls) {
        Validate.notNull(cls, "The class must not be null");
        final List<Field> allFields = new ArrayList<>();
        Class<?> currentClass = cls;
        while (currentClass != null) {
            final Field[] declaredFields = currentClass.getDeclaredFields();
            Collections.addAll(allFields, declaredFields);
            currentClass = currentClass.getSuperclass();
        }
        return allFields;
    }

    
Gets all fields of the given class and its parents (if any) that are annotated with the given annotation.
Params:
cls –  the Class to query
annotationCls –  the Annotation that must be present on a field to be matched
Throws:
IllegalArgumentException –  if the class or annotation are null
Returns:
an array of Fields (possibly empty).
Since:
3.4/**
     * Gets all fields of the given class and its parents (if any) that are annotated with the given annotation.
     * @param cls
     *            the {@link Class} to query
     * @param annotationCls
     *            the {@link Annotation} that must be present on a field to be matched
     * @return an array of Fields (possibly empty).
     * @throws IllegalArgumentException
     *            if the class or annotation are {@code null}
     * @since 3.4
     */
    public static Field[] getFieldsWithAnnotation(final Class<?> cls, final Class<? extends Annotation> annotationCls) {
        final List<Field> annotatedFieldsList = getFieldsListWithAnnotation(cls, annotationCls);
        return annotatedFieldsList.toArray(ArrayUtils.EMPTY_FIELD_ARRAY);
    }

    
Gets all fields of the given class and its parents (if any) that are annotated with the given annotation.
Params:
cls –  the Class to query
annotationCls –  the Annotation that must be present on a field to be matched
Throws:
IllegalArgumentException –  if the class or annotation are null
Returns:
a list of Fields (possibly empty).
Since:
3.4/**
     * Gets all fields of the given class and its parents (if any) that are annotated with the given annotation.
     * @param cls
     *            the {@link Class} to query
     * @param annotationCls
     *            the {@link Annotation} that must be present on a field to be matched
     * @return a list of Fields (possibly empty).
     * @throws IllegalArgumentException
     *            if the class or annotation are {@code null}
     * @since 3.4
     */
    public static List<Field> getFieldsListWithAnnotation(final Class<?> cls, final Class<? extends Annotation> annotationCls) {
        Validate.notNull(annotationCls, "The annotation class must not be null");
        final List<Field> allFields = getAllFieldsList(cls);
        final List<Field> annotatedFields = new ArrayList<>();
        for (final Field field : allFields) {
            if (field.getAnnotation(annotationCls) != null) {
                annotatedFields.add(field);
            }
        }
        return annotatedFields;
    }

    
Reads an accessible static Field. 
Params:
field – 
           to read
Throws:
IllegalArgumentException –  if the field is null, or not static
IllegalAccessException – 
            if the field is not accessible
Returns:
the field value/**
     * Reads an accessible {@code static} {@link Field}.
     *
     * @param field
     *            to read
     * @return the field value
     * @throws IllegalArgumentException
     *             if the field is {@code null}, or not {@code static}
     * @throws IllegalAccessException
     *             if the field is not accessible
     */
    public static Object readStaticField(final Field field) throws IllegalAccessException {
        return readStaticField(field, false);
    }

    
Reads a static Field. 
Params:
field – 
           to read
forceAccess –  whether to break scope restrictions using the AccessibleObject.setAccessible(boolean) method.
Throws:
IllegalArgumentException –  if the field is null or not static
IllegalAccessException – 
            if the field is not made accessible
Returns:
the field value/**
     * Reads a static {@link Field}.
     *
     * @param field
     *            to read
     * @param forceAccess
     *            whether to break scope restrictions using the
     *            {@link java.lang.reflect.AccessibleObject#setAccessible(boolean)} method.
     * @return the field value
     * @throws IllegalArgumentException
     *             if the field is {@code null} or not {@code static}
     * @throws IllegalAccessException
     *             if the field is not made accessible
     */
    public static Object readStaticField(final Field field, final boolean forceAccess) throws IllegalAccessException {
        Validate.notNull(field, "The field must not be null");
        Validate.isTrue(Modifier.isStatic(field.getModifiers()), "The field '%s' is not static", field.getName());
        return readField(field, (Object) null, forceAccess);
    }

    
Reads the named public static Field. Superclasses will be considered. 
Params:
cls –  the Class to reflect, must not be null
fieldName – 
           the field name to obtain
Throws:
IllegalArgumentException –  if the class is null, or the field name is blank or empty, is not static, or could not be found
IllegalAccessException – 
            if the field is not accessible
Returns:
the value of the field/**
     * Reads the named {@code public static} {@link Field}. Superclasses will be considered.
     *
     * @param cls
     *            the {@link Class} to reflect, must not be {@code null}
     * @param fieldName
     *            the field name to obtain
     * @return the value of the field
     * @throws IllegalArgumentException
     *             if the class is {@code null}, or the field name is blank or empty, is not {@code static}, or could
     *             not be found
     * @throws IllegalAccessException
     *             if the field is not accessible
     */
    public static Object readStaticField(final Class<?> cls, final String fieldName) throws IllegalAccessException {
        return readStaticField(cls, fieldName, false);
    }

    
Reads the named static Field. Superclasses will be considered. 
Params:
cls –  the Class to reflect, must not be null
fieldName – 
           the field name to obtain
forceAccess –  whether to break scope restrictions using the AccessibleObject.setAccessible(boolean) method. false will only match public fields.
Throws:
IllegalArgumentException –  if the class is null, or the field name is blank or empty, is not static, or could not be found
IllegalAccessException – 
            if the field is not made accessible
Returns:
the Field object/**
     * Reads the named {@code static} {@link Field}. Superclasses will be considered.
     *
     * @param cls
     *            the {@link Class} to reflect, must not be {@code null}
     * @param fieldName
     *            the field name to obtain
     * @param forceAccess
     *            whether to break scope restrictions using the
     *            {@link java.lang.reflect.AccessibleObject#setAccessible(boolean)} method. {@code false} will only
     *            match {@code public} fields.
     * @return the Field object
     * @throws IllegalArgumentException
     *             if the class is {@code null}, or the field name is blank or empty, is not {@code static}, or could
     *             not be found
     * @throws IllegalAccessException
     *             if the field is not made accessible
     */
    public static Object readStaticField(final Class<?> cls, final String fieldName, final boolean forceAccess) throws IllegalAccessException {
        final Field field = getField(cls, fieldName, forceAccess);
        Validate.notNull(field, "Cannot locate field '%s' on %s", fieldName, cls);
        // already forced access above, don't repeat it here:
        return readStaticField(field, false);
    }

    
Gets the value of a static Field by name. The field must be public. Only the specified class will be considered. 
Params:
cls –  the Class to reflect, must not be null
fieldName – 
           the field name to obtain
Throws:
IllegalArgumentException –  if the class is null, or the field name is blank or empty, is not static, or could not be found
IllegalAccessException – 
            if the field is not accessible
Returns:
the value of the field/**
     * Gets the value of a {@code static} {@link Field} by name. The field must be {@code public}. Only the specified
     * class will be considered.
     *
     * @param cls
     *            the {@link Class} to reflect, must not be {@code null}
     * @param fieldName
     *            the field name to obtain
     * @return the value of the field
     * @throws IllegalArgumentException
     *             if the class is {@code null}, or the field name is blank or empty, is not {@code static}, or could
     *             not be found
     * @throws IllegalAccessException
     *             if the field is not accessible
     */
    public static Object readDeclaredStaticField(final Class<?> cls, final String fieldName) throws IllegalAccessException {
        return readDeclaredStaticField(cls, fieldName, false);
    }

    
Gets the value of a static Field by name. Only the specified class will be considered. 
Params:
cls –  the Class to reflect, must not be null
fieldName – 
           the field name to obtain
forceAccess –  whether to break scope restrictions using the AccessibleObject.setAccessible(boolean) method. false will only match public fields.
Throws:
IllegalArgumentException –  if the class is null, or the field name is blank or empty, is not static, or could not be found
IllegalAccessException – 
            if the field is not made accessible
Returns:
the Field object/**
     * Gets the value of a {@code static} {@link Field} by name. Only the specified class will be considered.
     *
     * @param cls
     *            the {@link Class} to reflect, must not be {@code null}
     * @param fieldName
     *            the field name to obtain
     * @param forceAccess
     *            whether to break scope restrictions using the
     *            {@link java.lang.reflect.AccessibleObject#setAccessible(boolean)} method. {@code false} will only
     *            match {@code public} fields.
     * @return the Field object
     * @throws IllegalArgumentException
     *             if the class is {@code null}, or the field name is blank or empty, is not {@code static}, or could
     *             not be found
     * @throws IllegalAccessException
     *             if the field is not made accessible
     */
    public static Object readDeclaredStaticField(final Class<?> cls, final String fieldName, final boolean forceAccess) throws IllegalAccessException {
        final Field field = getDeclaredField(cls, fieldName, forceAccess);
        Validate.notNull(field, "Cannot locate declared field %s.%s", cls.getName(), fieldName);
        // already forced access above, don't repeat it here:
        return readStaticField(field, false);
    }

    
Reads an accessible Field. 
Params:
field – 
           the field to use
target –  the object to call on, may be null for static fields
Throws:
IllegalArgumentException –  if the field is null
IllegalAccessException – 
            if the field is not accessible
Returns:
the field value/**
     * Reads an accessible {@link Field}.
     *
     * @param field
     *            the field to use
     * @param target
     *            the object to call on, may be {@code null} for {@code static} fields
     * @return the field value
     * @throws IllegalArgumentException
     *             if the field is {@code null}
     * @throws IllegalAccessException
     *             if the field is not accessible
     */
    public static Object readField(final Field field, final Object target) throws IllegalAccessException {
        return readField(field, target, false);
    }

    
Reads a Field. 
Params:
field – 
           the field to use
target –  the object to call on, may be null for static fields
forceAccess –  whether to break scope restrictions using the AccessibleObject.setAccessible(boolean) method.
Throws:
IllegalArgumentException –  if the field is null
IllegalAccessException – 
            if the field is not made accessible
Returns:
the field value/**
     * Reads a {@link Field}.
     *
     * @param field
     *            the field to use
     * @param target
     *            the object to call on, may be {@code null} for {@code static} fields
     * @param forceAccess
     *            whether to break scope restrictions using the
     *            {@link java.lang.reflect.AccessibleObject#setAccessible(boolean)} method.
     * @return the field value
     * @throws IllegalArgumentException
     *             if the field is {@code null}
     * @throws IllegalAccessException
     *             if the field is not made accessible
     */
    public static Object readField(final Field field, final Object target, final boolean forceAccess) throws IllegalAccessException {
        Validate.notNull(field, "The field must not be null");
        if (forceAccess && !field.isAccessible()) {
            field.setAccessible(true);
        } else {
            MemberUtils.setAccessibleWorkaround(field);
        }
        return field.get(target);
    }

    
Reads the named public Field. Superclasses will be considered. 
Params:
target –  the object to reflect, must not be null
fieldName – 
           the field name to obtain
Throws:
IllegalArgumentException –  if the class is null, or the field name is blank or empty or could not be found
IllegalAccessException –  if the named field is not public
Returns:
the value of the field/**
     * Reads the named {@code public} {@link Field}. Superclasses will be considered.
     *
     * @param target
     *            the object to reflect, must not be {@code null}
     * @param fieldName
     *            the field name to obtain
     * @return the value of the field
     * @throws IllegalArgumentException
     *             if the class is {@code null}, or the field name is blank or empty or could not be found
     * @throws IllegalAccessException
     *             if the named field is not {@code public}
     */
    public static Object readField(final Object target, final String fieldName) throws IllegalAccessException {
        return readField(target, fieldName, false);
    }

    
Reads the named Field. Superclasses will be considered. 
Params:
target –  the object to reflect, must not be null
fieldName – 
           the field name to obtain
forceAccess –  whether to break scope restrictions using the AccessibleObject.setAccessible(boolean) method. false will only match public fields.
Throws:
IllegalArgumentException –  if target is null, or the field name is blank or empty or could not be found
IllegalAccessException – 
            if the named field is not made accessible
Returns:
the field value/**
     * Reads the named {@link Field}. Superclasses will be considered.
     *
     * @param target
     *            the object to reflect, must not be {@code null}
     * @param fieldName
     *            the field name to obtain
     * @param forceAccess
     *            whether to break scope restrictions using the
     *            {@link java.lang.reflect.AccessibleObject#setAccessible(boolean)} method. {@code false} will only
     *            match {@code public} fields.
     * @return the field value
     * @throws IllegalArgumentException
     *             if {@code target} is {@code null}, or the field name is blank or empty or could not be found
     * @throws IllegalAccessException
     *             if the named field is not made accessible
     */
    public static Object readField(final Object target, final String fieldName, final boolean forceAccess) throws IllegalAccessException {
        Validate.notNull(target, "target object must not be null");
        final Class<?> cls = target.getClass();
        final Field field = getField(cls, fieldName, forceAccess);
        Validate.isTrue(field != null, "Cannot locate field %s on %s", fieldName, cls);
        // already forced access above, don't repeat it here:
        return readField(field, target, false);
    }

    
Reads the named public Field. Only the class of the specified object will be considered. 
Params:
target –  the object to reflect, must not be null
fieldName – 
           the field name to obtain
Throws:
IllegalArgumentException –  if target is null, or the field name is blank or empty or could not be found
IllegalAccessException –  if the named field is not public
Returns:
the value of the field/**
     * Reads the named {@code public} {@link Field}. Only the class of the specified object will be considered.
     *
     * @param target
     *            the object to reflect, must not be {@code null}
     * @param fieldName
     *            the field name to obtain
     * @return the value of the field
     * @throws IllegalArgumentException
     *             if {@code target} is {@code null}, or the field name is blank or empty or could not be found
     * @throws IllegalAccessException
     *             if the named field is not {@code public}
     */
    public static Object readDeclaredField(final Object target, final String fieldName) throws IllegalAccessException {
        return readDeclaredField(target, fieldName, false);
    }

    
Gets a Field value by name. Only the class of the specified object will be considered. 
Params:
target –  the object to reflect, must not be null
fieldName – 
           the field name to obtain
forceAccess –  whether to break scope restrictions using the AccessibleObject.setAccessible(boolean) method. false will only match public fields.
Throws:
IllegalArgumentException –  if target is null, or the field name is blank or empty or could not be found
IllegalAccessException – 
            if the field is not made accessible
Returns:
the Field object/**
     * Gets a {@link Field} value by name. Only the class of the specified object will be considered.
     *
     * @param target
     *            the object to reflect, must not be {@code null}
     * @param fieldName
     *            the field name to obtain
     * @param forceAccess
     *            whether to break scope restrictions using the
     *            {@link java.lang.reflect.AccessibleObject#setAccessible(boolean)} method. {@code false} will only
     *            match public fields.
     * @return the Field object
     * @throws IllegalArgumentException
     *             if {@code target} is {@code null}, or the field name is blank or empty or could not be found
     * @throws IllegalAccessException
     *             if the field is not made accessible
     */
    public static Object readDeclaredField(final Object target, final String fieldName, final boolean forceAccess) throws IllegalAccessException {
        Validate.notNull(target, "target object must not be null");
        final Class<?> cls = target.getClass();
        final Field field = getDeclaredField(cls, fieldName, forceAccess);
        Validate.isTrue(field != null, "Cannot locate declared field %s.%s", cls, fieldName);
        // already forced access above, don't repeat it here:
        return readField(field, target, false);
    }

    
Writes a public static Field. 
Params:
field – 
           to write
value – 
           to set
Throws:
IllegalArgumentException –  if the field is null or not static, or value is not assignable
IllegalAccessException –  if the field is not public or is final/**
     * Writes a {@code public static} {@link Field}.
     *
     * @param field
     *            to write
     * @param value
     *            to set
     * @throws IllegalArgumentException
     *             if the field is {@code null} or not {@code static}, or {@code value} is not assignable
     * @throws IllegalAccessException
     *             if the field is not {@code public} or is {@code final}
     */
    public static void writeStaticField(final Field field, final Object value) throws IllegalAccessException {
        writeStaticField(field, value, false);
    }

    
Writes a static Field. 
Params:
field – 
           to write
value – 
           to set
forceAccess –  whether to break scope restrictions using the AccessibleObject.setAccessible(boolean) method. false will only match public fields.
Throws:
IllegalArgumentException –  if the field is null or not static, or value is not assignable
IllegalAccessException –  if the field is not made accessible or is final/**
     * Writes a static {@link Field}.
     *
     * @param field
     *            to write
     * @param value
     *            to set
     * @param forceAccess
     *            whether to break scope restrictions using the
     *            {@link java.lang.reflect.AccessibleObject#setAccessible(boolean)} method. {@code false} will only
     *            match {@code public} fields.
     * @throws IllegalArgumentException
     *             if the field is {@code null} or not {@code static}, or {@code value} is not assignable
     * @throws IllegalAccessException
     *             if the field is not made accessible or is {@code final}
     */
    public static void writeStaticField(final Field field, final Object value, final boolean forceAccess) throws IllegalAccessException {
        Validate.notNull(field, "The field must not be null");
        Validate.isTrue(Modifier.isStatic(field.getModifiers()), "The field %s.%s is not static", field.getDeclaringClass().getName(),
                field.getName());
        writeField(field, (Object) null, value, forceAccess);
    }

    
Writes a named public static Field. Superclasses will be considered. 
Params:
cls –  Class on which the field is to be found
fieldName – 
           to write
value – 
           to set
Throws:
IllegalArgumentException –  if cls is null, the field name is blank or empty, the field cannot be located or is not static, or value is not assignable
IllegalAccessException –  if the field is not public or is final/**
     * Writes a named {@code public static} {@link Field}. Superclasses will be considered.
     *
     * @param cls
     *            {@link Class} on which the field is to be found
     * @param fieldName
     *            to write
     * @param value
     *            to set
     * @throws IllegalArgumentException
     *             if {@code cls} is {@code null}, the field name is blank or empty, the field cannot be located or is
     *             not {@code static}, or {@code value} is not assignable
     * @throws IllegalAccessException
     *             if the field is not {@code public} or is {@code final}
     */
    public static void writeStaticField(final Class<?> cls, final String fieldName, final Object value) throws IllegalAccessException {
        writeStaticField(cls, fieldName, value, false);
    }

    
Writes a named static Field. Superclasses will be considered. 
Params:
cls –  Class on which the field is to be found
fieldName – 
           to write
value – 
           to set
forceAccess –  whether to break scope restrictions using the AccessibleObject.setAccessible(boolean) method. false will only match public fields.
Throws:
IllegalArgumentException –  if cls is null, the field name is blank or empty, the field cannot be located or is not static, or value is not assignable
IllegalAccessException –  if the field is not made accessible or is final/**
     * Writes a named {@code static} {@link Field}. Superclasses will be considered.
     *
     * @param cls
     *            {@link Class} on which the field is to be found
     * @param fieldName
     *            to write
     * @param value
     *            to set
     * @param forceAccess
     *            whether to break scope restrictions using the
     *            {@link java.lang.reflect.AccessibleObject#setAccessible(boolean)} method. {@code false} will only
     *            match {@code public} fields.
     * @throws IllegalArgumentException
     *             if {@code cls} is {@code null}, the field name is blank or empty, the field cannot be located or is
     *             not {@code static}, or {@code value} is not assignable
     * @throws IllegalAccessException
     *             if the field is not made accessible or is {@code final}
     */
    public static void writeStaticField(final Class<?> cls, final String fieldName, final Object value, final boolean forceAccess)
            throws IllegalAccessException {
        final Field field = getField(cls, fieldName, forceAccess);
        Validate.notNull(field, "Cannot locate field %s on %s", fieldName, cls);
        // already forced access above, don't repeat it here:
        writeStaticField(field, value, false);
    }

    
Writes a named public static Field. Only the specified class will be considered. 
Params:
cls –  Class on which the field is to be found
fieldName – 
           to write
value – 
           to set
Throws:
IllegalArgumentException –  if cls is null, the field name is blank or empty, the field cannot be located or is not static, or value is not assignable
IllegalAccessException –  if the field is not public or is final/**
     * Writes a named {@code public static} {@link Field}. Only the specified class will be considered.
     *
     * @param cls
     *            {@link Class} on which the field is to be found
     * @param fieldName
     *            to write
     * @param value
     *            to set
     * @throws IllegalArgumentException
     *             if {@code cls} is {@code null}, the field name is blank or empty, the field cannot be located or is
     *             not {@code static}, or {@code value} is not assignable
     * @throws IllegalAccessException
     *             if the field is not {@code public} or is {@code final}
     */
    public static void writeDeclaredStaticField(final Class<?> cls, final String fieldName, final Object value) throws IllegalAccessException {
        writeDeclaredStaticField(cls, fieldName, value, false);
    }

    
Writes a named static Field. Only the specified class will be considered. 
Params:
cls –  Class on which the field is to be found
fieldName – 
           to write
value – 
           to set
forceAccess –  whether to break scope restrictions using the AccessibleObject#setAccessible(boolean) method. false will only match public fields.
Throws:
IllegalArgumentException –  if cls is null, the field name is blank or empty, the field cannot be located or is not static, or value is not assignable
IllegalAccessException –  if the field is not made accessible or is final/**
     * Writes a named {@code static} {@link Field}. Only the specified class will be considered.
     *
     * @param cls
     *            {@link Class} on which the field is to be found
     * @param fieldName
     *            to write
     * @param value
     *            to set
     * @param forceAccess
     *            whether to break scope restrictions using the {@code AccessibleObject#setAccessible(boolean)} method.
     *            {@code false} will only match {@code public} fields.
     * @throws IllegalArgumentException
     *             if {@code cls} is {@code null}, the field name is blank or empty, the field cannot be located or is
     *             not {@code static}, or {@code value} is not assignable
     * @throws IllegalAccessException
     *             if the field is not made accessible or is {@code final}
     */
    public static void writeDeclaredStaticField(final Class<?> cls, final String fieldName, final Object value, final boolean forceAccess)
            throws IllegalAccessException {
        final Field field = getDeclaredField(cls, fieldName, forceAccess);
        Validate.notNull(field, "Cannot locate declared field %s.%s", cls.getName(), fieldName);
        // already forced access above, don't repeat it here:
        writeField(field, (Object) null, value, false);
    }

    
Writes an accessible Field. 
Params:
field – 
           to write
target –  the object to call on, may be null for static fields
value – 
           to set
Throws:
IllegalAccessException –  if the field or target is null, the field is not accessible or is final, or value is not assignable/**
     * Writes an accessible {@link Field}.
     *
     * @param field
     *            to write
     * @param target
     *            the object to call on, may be {@code null} for {@code static} fields
     * @param value
     *            to set
     * @throws IllegalAccessException
     *             if the field or target is {@code null}, the field is not accessible or is {@code final}, or
     *             {@code value} is not assignable
     */
    public static void writeField(final Field field, final Object target, final Object value) throws IllegalAccessException {
        writeField(field, target, value, false);
    }

    
Writes a Field. 
Params:
field – 
           to write
target –  the object to call on, may be null for static fields
value – 
           to set
forceAccess –  whether to break scope restrictions using the AccessibleObject.setAccessible(boolean) method. false will only match public fields.
Throws:
IllegalArgumentException –  if the field is null or value is not assignable
IllegalAccessException –  if the field is not made accessible or is final/**
     * Writes a {@link Field}.
     *
     * @param field
     *            to write
     * @param target
     *            the object to call on, may be {@code null} for {@code static} fields
     * @param value
     *            to set
     * @param forceAccess
     *            whether to break scope restrictions using the
     *            {@link java.lang.reflect.AccessibleObject#setAccessible(boolean)} method. {@code false} will only
     *            match {@code public} fields.
     * @throws IllegalArgumentException
     *             if the field is {@code null} or {@code value} is not assignable
     * @throws IllegalAccessException
     *             if the field is not made accessible or is {@code final}
     */
    public static void writeField(final Field field, final Object target, final Object value, final boolean forceAccess)
            throws IllegalAccessException {
        Validate.notNull(field, "The field must not be null");
        if (forceAccess && !field.isAccessible()) {
            field.setAccessible(true);
        } else {
            MemberUtils.setAccessibleWorkaround(field);
        }
        field.set(target, value);
    }

    
Removes the final modifier from a Field. 
Params:
field – 
           to remove the final modifier
Throws:
IllegalArgumentException –  if the field is null
Since:
3.2/**
     * Removes the final modifier from a {@link Field}.
     *
     * @param field
     *            to remove the final modifier
     * @throws IllegalArgumentException
     *             if the field is {@code null}
     * @since 3.2
     */
    public static void removeFinalModifier(final Field field) {
        removeFinalModifier(field, true);
    }

    
Removes the final modifier from a Field. 
Params:
field – 
           to remove the final modifier
forceAccess –  whether to break scope restrictions using the AccessibleObject.setAccessible(boolean) method. false will only match public fields.
Throws:
IllegalArgumentException –  if the field is null
Deprecated:
As of Java 12, we can no longer drop the final modifier, thus rendering this method obsolete. The JDK discussion about this change can be found here: http://mail.openjdk.java.net/pipermail/core-libs-dev/2018-November/056486.html
Since:
3.3/**
     * Removes the final modifier from a {@link Field}.
     *
     * @param field
     *            to remove the final modifier
     * @param forceAccess
     *            whether to break scope restrictions using the
     *            {@link java.lang.reflect.AccessibleObject#setAccessible(boolean)} method. {@code false} will only
     *            match {@code public} fields.
     * @throws IllegalArgumentException
     *             if the field is {@code null}
     * @deprecated As of Java 12, we can no longer drop the {@code final} modifier, thus
     *             rendering this method obsolete. The JDK discussion about this change can be found
     *             here: http://mail.openjdk.java.net/pipermail/core-libs-dev/2018-November/056486.html
     * @since 3.3
     */
    @Deprecated
    public static void removeFinalModifier(final Field field, final boolean forceAccess) {
        Validate.notNull(field, "The field must not be null");

        try {
            if (Modifier.isFinal(field.getModifiers())) {
                // Do all JREs implement Field with a private ivar called "modifiers"?
                final Field modifiersField = Field.class.getDeclaredField("modifiers");
                final boolean doForceAccess = forceAccess && !modifiersField.isAccessible();
                if (doForceAccess) {
                    modifiersField.setAccessible(true);
                }
                try {
                    modifiersField.setInt(field, field.getModifiers() & ~Modifier.FINAL);
                } finally {
                    if (doForceAccess) {
                        modifiersField.setAccessible(false);
                    }
                }
            }
        } catch (final NoSuchFieldException | IllegalAccessException e) {
            if (SystemUtils.isJavaVersionAtLeast(JavaVersion.JAVA_12)) {
              throw new UnsupportedOperationException(
                  "In java 12+ final cannot be removed.",
                  e
              );
            }
            // else no exception is thrown because we can modify final.
        }
    }

    
Writes a public Field. Superclasses will be considered. 
Params:
target –  the object to reflect, must not be null
fieldName – 
           the field name to obtain
value – 
           to set
Throws:
IllegalArgumentException –  if target is null, fieldName is blank or empty or could not be found, or value is not assignable
IllegalAccessException – 
            if the field is not accessible/**
     * Writes a {@code public} {@link Field}. Superclasses will be considered.
     *
     * @param target
     *            the object to reflect, must not be {@code null}
     * @param fieldName
     *            the field name to obtain
     * @param value
     *            to set
     * @throws IllegalArgumentException
     *             if {@code target} is {@code null}, {@code fieldName} is blank or empty or could not be found, or
     *             {@code value} is not assignable
     * @throws IllegalAccessException
     *             if the field is not accessible
     */
    public static void writeField(final Object target, final String fieldName, final Object value) throws IllegalAccessException {
        writeField(target, fieldName, value, false);
    }

    
Writes a Field. Superclasses will be considered. 
Params:
target –  the object to reflect, must not be null
fieldName – 
           the field name to obtain
value – 
           to set
forceAccess –  whether to break scope restrictions using the AccessibleObject.setAccessible(boolean) method. false will only match public fields.
Throws:
IllegalArgumentException –  if target is null, fieldName is blank or empty or could not be found, or value is not assignable
IllegalAccessException – 
            if the field is not made accessible/**
     * Writes a {@link Field}. Superclasses will be considered.
     *
     * @param target
     *            the object to reflect, must not be {@code null}
     * @param fieldName
     *            the field name to obtain
     * @param value
     *            to set
     * @param forceAccess
     *            whether to break scope restrictions using the
     *            {@link java.lang.reflect.AccessibleObject#setAccessible(boolean)} method. {@code false} will only
     *            match {@code public} fields.
     * @throws IllegalArgumentException
     *             if {@code target} is {@code null}, {@code fieldName} is blank or empty or could not be found, or
     *             {@code value} is not assignable
     * @throws IllegalAccessException
     *             if the field is not made accessible
     */
    public static void writeField(final Object target, final String fieldName, final Object value, final boolean forceAccess)
            throws IllegalAccessException {
        Validate.notNull(target, "target object must not be null");
        final Class<?> cls = target.getClass();
        final Field field = getField(cls, fieldName, forceAccess);
        Validate.isTrue(field != null, "Cannot locate declared field %s.%s", cls.getName(), fieldName);
        // already forced access above, don't repeat it here:
        writeField(field, target, value, false);
    }

    
Writes a public Field. Only the specified class will be considered. 
Params:
target –  the object to reflect, must not be null
fieldName – 
           the field name to obtain
value – 
           to set
Throws:
IllegalArgumentException –  if target is null, fieldName is blank or empty or could not be found, or value is not assignable
IllegalAccessException – 
            if the field is not made accessible/**
     * Writes a {@code public} {@link Field}. Only the specified class will be considered.
     *
     * @param target
     *            the object to reflect, must not be {@code null}
     * @param fieldName
     *            the field name to obtain
     * @param value
     *            to set
     * @throws IllegalArgumentException
     *             if {@code target} is {@code null}, {@code fieldName} is blank or empty or could not be found, or
     *             {@code value} is not assignable
     * @throws IllegalAccessException
     *             if the field is not made accessible
     */
    public static void writeDeclaredField(final Object target, final String fieldName, final Object value) throws IllegalAccessException {
        writeDeclaredField(target, fieldName, value, false);
    }

    
Writes a public Field. Only the specified class will be considered. 
Params:
target –  the object to reflect, must not be null
fieldName – 
           the field name to obtain
value – 
           to set
forceAccess –  whether to break scope restrictions using the AccessibleObject.setAccessible(boolean) method. false will only match public fields.
Throws:
IllegalArgumentException –  if target is null, fieldName is blank or empty or could not be found, or value is not assignable
IllegalAccessException – 
            if the field is not made accessible/**
     * Writes a {@code public} {@link Field}. Only the specified class will be considered.
     *
     * @param target
     *            the object to reflect, must not be {@code null}
     * @param fieldName
     *            the field name to obtain
     * @param value
     *            to set
     * @param forceAccess
     *            whether to break scope restrictions using the
     *            {@link java.lang.reflect.AccessibleObject#setAccessible(boolean)} method. {@code false} will only
     *            match {@code public} fields.
     * @throws IllegalArgumentException
     *             if {@code target} is {@code null}, {@code fieldName} is blank or empty or could not be found, or
     *             {@code value} is not assignable
     * @throws IllegalAccessException
     *             if the field is not made accessible
     */
    public static void writeDeclaredField(final Object target, final String fieldName, final Object value, final boolean forceAccess)
            throws IllegalAccessException {
        Validate.notNull(target, "target object must not be null");
        final Class<?> cls = target.getClass();
        final Field field = getDeclaredField(cls, fieldName, forceAccess);
        Validate.isTrue(field != null, "Cannot locate declared field %s.%s", cls.getName(), fieldName);
        // already forced access above, don't repeat it here:
        writeField(field, target, value, false);
    }
}