package org.codehaus.plexus.interpolation.reflection;

/*
 * Copyright 2001-2006 Codehaus Foundation.
 *
 * Licensed 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.
 */
import org.codehaus.plexus.interpolation.util.StringUtils;

import java.lang.ref.WeakReference;
import java.lang.reflect.Array;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.List;
import java.util.Map;
import java.util.WeakHashMap;

NOTE: This class was copied from plexus-utils, to allow this library to stand completely self-contained.

Using simple dotted expressions extract the values from a MavenProject instance, For example we might want to extract a value like: project.build.sourceDirectory

Author:Jason van Zyl
/** * <b>NOTE:</b> This class was copied from plexus-utils, to allow this library to stand completely self-contained. * <p>Using simple dotted expressions extract the values from a MavenProject instance, For example we might want to extract * a value like: project.build.sourceDirectory</p> * * @author <a href="mailto:jason@maven.org">Jason van Zyl </a> */
public class ReflectionValueExtractor { private static final Class<?>[] CLASS_ARGS = new Class[0]; private static final Object[] OBJECT_ARGS = new Object[0];
Use a WeakHashMap here, so the keys (Class objects) can be garbage collected. This approach prevents permgen space overflows due to retention of discarded classloaders.
/** * Use a WeakHashMap here, so the keys (Class objects) can be garbage collected. This approach prevents permgen * space overflows due to retention of discarded classloaders. */
private static final Map<Class<?>, WeakReference<ClassMap>> classMaps = new WeakHashMap<Class<?>, WeakReference<ClassMap>>(); static final int EOF = -1; static final char PROPERTY_START = '.'; static final char INDEXED_START = '['; static final char INDEXED_END = ']'; static final char MAPPED_START = '('; static final char MAPPED_END = ')'; static class Tokenizer { final String expression; int idx; public Tokenizer( String expression ) { this.expression = expression; } public int peekChar() { return idx < expression.length() ? expression.charAt( idx ) : EOF; } public int skipChar() { return idx < expression.length() ? expression.charAt( idx++ ) : EOF; } public String nextToken( char delimiter ) { int start = idx; while ( idx < expression.length() && delimiter != expression.charAt( idx ) ) { idx++; } // delimiter MUST be present if ( idx <= start || idx >= expression.length() ) { return null; } return expression.substring( start, idx++ ); } public String nextPropertyName() { final int start = idx; while ( idx < expression.length() && Character.isJavaIdentifierPart( expression.charAt( idx ) ) ) { idx++; } // property name does not require delimiter if ( idx <= start || idx > expression.length() ) { return null; } return expression.substring( start, idx ); } public int getPosition() { return idx < expression.length() ? idx : EOF; } // to make tokenizer look pretty in debugger @Override public String toString() { return idx < expression.length() ? expression.substring( idx ) : "<EOF>"; } } private ReflectionValueExtractor() { }

The implementation supports indexed, nested and mapped properties.

  • nested properties should be defined by a dot, i.e. "user.address.street"
  • indexed properties (java.util.List or array instance) should be contains (\\w+)\\[(\\d+)\\] pattern, i.e. "user.addresses[1].street"
  • mapped properties should be contains (\\w+)\\((.+)\\) pattern, i.e. "user.addresses(myAddress).street"
Params:
  • expression – not null expression
  • root – not null object
Throws:
Returns:the object defined by the expression
/** * <p> * The implementation supports indexed, nested and mapped properties. * </p> * <ul> * <li>nested properties should be defined by a dot, i.e. "user.address.street"</li> * <li>indexed properties (java.util.List or array instance) should be contains <code>(\\w+)\\[(\\d+)\\]</code> * pattern, i.e. "user.addresses[1].street"</li> * <li>mapped properties should be contains <code>(\\w+)\\((.+)\\)</code> pattern, i.e. * "user.addresses(myAddress).street"</li> * </ul> * * @param expression not null expression * @param root not null object * @return the object defined by the expression * @throws Exception if any */
public static Object evaluate( String expression, Object root ) throws Exception { return evaluate( expression, root, true ); }

The implementation supports indexed, nested and mapped properties.

  • nested properties should be defined by a dot, i.e. "user.address.street"
  • indexed properties (java.util.List or array instance) should be contains (\\w+)\\[(\\d+)\\] pattern, i.e. "user.addresses[1].street"
  • mapped properties should be contains (\\w+)\\((.+)\\) pattern, i.e. "user.addresses(myAddress).street"
Params:
  • expression – not null expression
  • root – not null object
  • trimRootToken – trim the token or not.
Throws:
Returns:the object defined by the expression
/** * <p> * The implementation supports indexed, nested and mapped properties. * </p> * <ul> * <li>nested properties should be defined by a dot, i.e. "user.address.street"</li> * <li>indexed properties (java.util.List or array instance) should be contains <code>(\\w+)\\[(\\d+)\\]</code> * pattern, i.e. "user.addresses[1].street"</li> * <li>mapped properties should be contains <code>(\\w+)\\((.+)\\)</code> pattern, i.e. * "user.addresses(myAddress).street"</li> * </ul> * * @param expression not null expression * @param root not null object * @param trimRootToken trim the token or not. * @return the object defined by the expression * @throws Exception if any */
// TODO: don't throw Exception public static Object evaluate( String expression, final Object root, final boolean trimRootToken ) throws Exception { Object value = root; // ---------------------------------------------------------------------- // Walk the dots and retrieve the ultimate value desired from the // MavenProject instance. // ---------------------------------------------------------------------- if ( expression == null || "".equals( expression.trim() ) || !Character.isJavaIdentifierStart( expression.charAt( 0 ) ) ) { return null; } boolean hasDots = expression.indexOf( PROPERTY_START ) >= 0; final Tokenizer tokenizer; if ( trimRootToken && hasDots ) { tokenizer = new Tokenizer( expression ); tokenizer.nextPropertyName(); if ( tokenizer.getPosition() == EOF ) { return null; } } else { tokenizer = new Tokenizer( "." + expression ); } int propertyPosition = tokenizer.getPosition(); while ( value != null && tokenizer.peekChar() != EOF ) { switch ( tokenizer.skipChar() ) { case INDEXED_START: value = getIndexedValue( expression, propertyPosition, tokenizer.getPosition(), value, tokenizer.nextToken( INDEXED_END ) ); break; case MAPPED_START: value = getMappedValue( expression, propertyPosition, tokenizer.getPosition(), value, tokenizer.nextToken( MAPPED_END ) ); break; case PROPERTY_START: propertyPosition = tokenizer.getPosition(); value = getPropertyValue( value, tokenizer.nextPropertyName() ); break; default: // could not parse expression return null; } } return value; } private static Object getMappedValue( final String expression, final int from, final int to, final Object value, final String key ) throws Exception { if ( value == null || key == null ) { return null; } if ( value instanceof Map ) { Object[] localParams = new Object[] { key }; ClassMap classMap = getClassMap( value.getClass() ); Method method = classMap.findMethod( "get", localParams ); return method.invoke( value, localParams ); } final String message = String.format( "The token '%s' at position '%d' refers to a java.util.Map, but the value seems is an instance of '%s'", expression.subSequence( from, to ), from, value.getClass() ); throw new Exception( message ); } private static Object getIndexedValue( final String expression, final int from, final int to, final Object value, final String indexStr ) throws Exception { try { int index = Integer.parseInt( indexStr ); if ( value.getClass().isArray() ) { return Array.get( value, index ); } if ( value instanceof List ) { ClassMap classMap = getClassMap( value.getClass() ); // use get method on List interface Object[] localParams = new Object[] { index }; Method method = classMap.findMethod( "get", localParams ); return method.invoke( value, localParams ); } } catch ( NumberFormatException e ) { return null; } catch ( InvocationTargetException e ) { // catch array index issues gracefully, otherwise release if ( e.getCause() instanceof IndexOutOfBoundsException ) { return null; } throw e; } final String message = String.format( "The token '%s' at position '%d' refers to a java.util.List or an array, but the value seems is an instance of '%s'", expression.subSequence( from, to ), from, value.getClass() ); throw new Exception( message ); } private static Object getPropertyValue( Object value, String property ) throws Exception { if ( value == null || property == null ) { return null; } ClassMap classMap = getClassMap( value.getClass() ); String methodBase = StringUtils.capitalizeFirstLetter( property ); String methodName = "get" + methodBase; Method method = classMap.findMethod( methodName, CLASS_ARGS ); if ( method == null ) { // perhaps this is a boolean property?? methodName = "is" + methodBase; method = classMap.findMethod( methodName, CLASS_ARGS ); } if ( method == null ) { return null; } try { return method.invoke( value, OBJECT_ARGS ); } catch ( InvocationTargetException e ) { throw e; } } private static ClassMap getClassMap( Class<?> clazz ) { WeakReference<ClassMap> softRef = classMaps.get( clazz ); ClassMap classMap; if ( softRef == null || ( classMap = softRef.get() ) == null ) { classMap = new ClassMap( clazz ); classMaps.put( clazz, new WeakReference<ClassMap>( classMap ) ); } return classMap; } }