https://ant.apache.org/: master POM (The Apache Software Foundation) 
/*
 *  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
 *
 *      https://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.tools.ant.taskdefs;

import org.apache.tools.ant.BuildException;
import org.apache.tools.ant.ExitStatusException;
import org.apache.tools.ant.Project;
import org.apache.tools.ant.PropertyHelper;
import org.apache.tools.ant.Task;
import org.apache.tools.ant.taskdefs.condition.Condition;
import org.apache.tools.ant.taskdefs.condition.ConditionBase;


Exits the active build, giving an additional message
if available.
The if and unless attributes make the
failure conditional -both probe for the named property being defined.
The if tests for the property being defined, the
unless for a property being undefined.
If both attributes are set, then the test fails only if both tests
are true. i.e.

fail := defined(ifProperty) && !defined(unlessProperty)

A single nested<condition> element can be specified
instead of using if/unless (a combined
effect can be achieved using isset conditions).

Since:Ant 1.2
@ant.taskname="fail" category="control"
/**
 * Exits the active build, giving an additional message
 * if available.
 *
 * The <code>if</code> and <code>unless</code> attributes make the
 * failure conditional -both probe for the named property being defined.
 * The <code>if</code> tests for the property being defined, the
 * <code>unless</code> for a property being undefined.
 *
 * If both attributes are set, then the test fails only if both tests
 * are true. i.e.
 * <pre>fail := defined(ifProperty) &amp;&amp; !defined(unlessProperty)</pre>
 *
 * A single nested<code>&lt;condition&gt;</code> element can be specified
 * instead of using <code>if</code>/<code>unless</code> (a combined
 * effect can be achieved using <code>isset</code> conditions).
 *
 * @since Ant 1.2
 *
 * @ant.task name="fail" category="control"
 */
public class Exit extends Task {

    private static class NestedCondition extends ConditionBase implements Condition {
        @Override
        public boolean eval() {
            if (countConditions() != 1) {
                throw new BuildException(
                    "A single nested condition is required.");
            }
            return getConditions().nextElement().eval();
        }
    }

    private String message;
    private Object ifCondition, unlessCondition;
    private NestedCondition nestedCondition;
    private Integer status;

    
A message giving further information on why the build exited.

Params:
  • value – message to output
/**
     * A message giving further information on why the build exited.
     *
     * @param value message to output
     */
    public void setMessage(String value) {
        this.message = value;
    }

    
Only fail if the given expression evaluates to true or the name
of an existing property.

Params:
  • c – property name or evaluated expression
Since:Ant 1.8.0
/**
     * Only fail if the given expression evaluates to true or the name
     * of an existing property.
     * @param c property name or evaluated expression
     * @since Ant 1.8.0
     */
    public void setIf(Object c) {
        ifCondition = c;
    }

    
Only fail if the given expression evaluates to true or the name
of an existing property.

Params:
  • c – property name or evaluated expression
/**
     * Only fail if the given expression evaluates to true or the name
     * of an existing property.
     * @param c property name or evaluated expression
     */
    public void setIf(String c) {
        setIf((Object) c);
    }

    
Only fail if the given expression evaluates to false or tno
property of the given name exists.

Params:
  • c – property name or evaluated expression
Since:Ant 1.8.0
/**
     * Only fail if the given expression evaluates to false or tno
     * property of the given name exists.
     * @param c property name or evaluated expression
     * @since Ant 1.8.0
     */
    public void setUnless(Object c) {
        unlessCondition = c;
    }

    
Only fail if the given expression evaluates to false or tno
property of the given name exists.

Params:
  • c – property name or evaluated expression
/**
     * Only fail if the given expression evaluates to false or tno
     * property of the given name exists.
     * @param c property name or evaluated expression
     */
    public void setUnless(String c) {
        setUnless((Object) c);
    }

    
Set the status code to associate with the thrown Exception.

Params:
  • i –   the int status
/**
     * Set the status code to associate with the thrown Exception.
     * @param i   the <code>int</code> status
     */
    public void setStatus(int i) {
        status = i;
    }

    
Throw a BuildException to exit (fail) the build.
If specified, evaluate conditions:
A single nested condition is accepted, but requires that the
if/unless attributes be omitted.
If the nested condition evaluates to true, or the
ifCondition is true or unlessCondition is false, the build will exit.
The error message is constructed from the text fields, from
the nested condition (if specified), or finally from
the if and unless parameters (if present).

Throws:
  • BuildException – on error
/**
     * Throw a <code>BuildException</code> to exit (fail) the build.
     * If specified, evaluate conditions:
     * A single nested condition is accepted, but requires that the
     * <code>if</code>/<code>unless</code> attributes be omitted.
     * If the nested condition evaluates to true, or the
     * ifCondition is true or unlessCondition is false, the build will exit.
     * The error message is constructed from the text fields, from
     * the nested condition (if specified), or finally from
     * the if and unless parameters (if present).
     * @throws BuildException on error
     */
    @Override
    public void execute() throws BuildException {
        boolean fail = (nestedConditionPresent()) ? testNestedCondition()
                     : (testIfCondition() && testUnlessCondition());
        if (fail) {
            String text = null;
            if (message != null && !message.trim().isEmpty()) {
                text = message.trim();
            } else {
                if (!isNullOrEmpty(ifCondition) && testIfCondition()) {
                    text = "if=" + ifCondition;
                }
                if (!isNullOrEmpty(unlessCondition) && testUnlessCondition()) {
                    if (text == null) {
                        text = "";
                    } else {
                        text += " and ";
                    }
                    text += "unless=" + unlessCondition;
                }
                if (nestedConditionPresent()) {
                    text = "condition satisfied";
                } else if (text == null) {
                    text = "No message";
                }
            }
            log("failing due to " + text, Project.MSG_DEBUG);
            throw status == null ? new BuildException(text)
                : new ExitStatusException(text, status);
        }
    }

    private boolean isNullOrEmpty(Object value) {
        return value == null || "".equals(value);
    }

    
Set a multiline message.

Params:
  • msg – the message to display
/**
     * Set a multiline message.
     * @param msg the message to display
     */
    public void addText(String msg) {
        if (message == null) {
            message = "";
        }
        message += getProject().replaceProperties(msg);
    }

    
Add a condition element.

Returns:ConditionBase.
Since:Ant 1.6.2
/**
     * Add a condition element.
     * @return <code>ConditionBase</code>.
     * @since Ant 1.6.2
     */
    public ConditionBase createCondition() {
        if (nestedCondition != null) {
            throw new BuildException("Only one nested condition is allowed.");
        }
        nestedCondition = new NestedCondition();
        return nestedCondition;
    }

    
test the if condition

Returns:true if there is no if condition, or the named property exists
/**
     * test the if condition
     * @return true if there is no if condition, or the named property exists
     */
    private boolean testIfCondition() {
        return PropertyHelper.getPropertyHelper(getProject())
            .testIfCondition(ifCondition);
    }

    
test the unless condition

Returns:true if there is no unless condition,
 or there is a named property but it doesn't exist
/**
     * test the unless condition
     * @return true if there is no unless condition,
     *  or there is a named property but it doesn't exist
     */
    private boolean testUnlessCondition() {
        return PropertyHelper.getPropertyHelper(getProject())
            .testUnlessCondition(unlessCondition);
    }

    
test the nested condition

Returns:true if there is none, or it evaluates to true
/**
     * test the nested condition
     * @return true if there is none, or it evaluates to true
     */
    private boolean testNestedCondition() {
        boolean result = nestedConditionPresent();

        if (result && ifCondition != null || unlessCondition != null) {
            throw new BuildException(
                "Nested conditions not permitted in conjunction with if/unless attributes");
        }

        return result && nestedCondition.eval();
    }

    
test whether there is a nested condition.

Returns:boolean.
/**
     * test whether there is a nested condition.
     * @return <code>boolean</code>.
     */
    private boolean nestedConditionPresent() {
        return (nestedCondition != null);
    }

}