如何从Java类获取多值并在Ant的build.xml中作为属性使用？

需要从Java类中获取多个值，作为Ant任务（build.xml）的属性使用。现有代码如下：

exampleClass.java #

String key1 = "my.test.key1";
String value1 = "my.test.value1";
String key2 = "my.test.key2";
String value2 = "my.test.value2";

Properties systemProperties = System.getProperties();
systemProperties.put(key1, value1);
systemProperties.put(key2, value2);
System.setProperties(systemProperties);

build.xml #

<macrodef name="nexDecryptingPwds">
  <sequential>
    <java classname="my.util.exec.exampleClass" fork="true" failonerror="false">
      <classpath>
        <fileset dir="${install.dir}/lib/">
          <include name="**/*.jar" />
        </fileset>
        <pathelement location="${basedir}" />
      </classpath>
    </java>
  </sequential>
</macrodef>

<echo message="my.test.key1: ${my.test.key1}" />
<echo message="my.test.key2: ${my.test.key2}" />

目前无法获取上述两个键对应的值，已知resultproperty属性一次只能获取一个值，请问该如何解决？

核心问题在于使用了fork="true"，这会让Java程序在独立进程中运行，它设置的系统属性无法传递回Ant主进程，导致Ant读取不到。以下是三种可行的解决方式：

方式一：Java类输出键值对，Ant解析输出 #

1. 修改exampleClass.java，将键值对以key=value格式输出到标准输出：

String key1 = "my.test.key1";
String value1 = "my.test.value1";
String key2 = "my.test.key2";
String value2 = "my.test.value2";

// 每行输出一个键值对
System.out.println(key1 + "=" + value1);
System.out.println(key2 + "=" + value2);

2. 修改build.xml，用outputproperty捕获Java程序的输出，再通过loadproperties转化为Ant属性：

<macrodef name="nexDecryptingPwds">
  <sequential>
    <java classname="my.util.exec.exampleClass" fork="true" failonerror="false" outputproperty="props.output">
      <classpath>
        <fileset dir="${install.dir}/lib/">
          <include name="**/*.jar" />
        </fileset>
        <pathelement location="${basedir}" />
      </classpath>
    </java>
    <!-- 将输出内容转为Ant属性 -->
    <loadproperties>
      <string value="${props.output}" />
    </loadproperties>
  </sequential>
</macrodef>

<!-- 先调用宏定义生成属性，再输出 -->
<nexDecryptingPwds />
<echo message="my.test.key1: ${my.test.key1}" />
<echo message="my.test.key2: ${my.test.key2}" />

方式二：取消进程隔离，让Java类在Ant进程内运行 #

如果Java类没有依赖冲突或特殊进程隔离需求，直接去掉fork="true"，这样Java类设置的系统属性会直接在Ant进程中生效：

<macrodef name="nexDecryptingPwds">
  <sequential>
    <java classname="my.util.exec.exampleClass" fork="false" failonerror="false">
      <classpath>
        <fileset dir="${install.dir}/lib/">
          <include name="**/*.jar" />
        </fileset>
        <pathelement location="${basedir}" />
      </classpath>
    </java>
  </sequential>
</macrodef>

<nexDecryptingPwds />
<echo message="my.test.key1: ${my.test.key1}" />
<echo message="my.test.key2: ${my.test.key2}" />

方式三：Java类写入属性文件，Ant加载文件 #

1. 修改exampleClass.java，将键值对写入临时属性文件：

import java.io.FileOutputStream;
import java.util.Properties;

public class exampleClass {
    public static void main(String[] args) throws Exception {
        String key1 = "my.test.key1";
        String value1 = "my.test.value1";
        String key2 = "my.test.key2";
        String value2 = "my.test.value2";

        Properties props = new Properties();
        props.put(key1, value1);
        props.put(key2, value2);
        // 写入临时属性文件
        props.store(new FileOutputStream("temp.properties"), "Generated properties");
    }
}

2. 修改build.xml，执行Java任务后加载该属性文件，可选删除临时文件：

<macrodef name="nexDecryptingPwds">
  <sequential>
    <java classname="my.util.exec.exampleClass" fork="true" failonerror="false">
      <classpath>
        <fileset dir="${install.dir}/lib/">
          <include name="**/*.jar" />
        </fileset>
        <pathelement location="${basedir}" />
      </classpath>
    </java>
    <!-- 加载生成的属性文件 -->
    <loadproperties srcfile="temp.properties" />
    <!-- 可选：清理临时文件 -->
    <delete file="temp.properties" />
  </sequential>
</macrodef>

<nexDecryptingPwds />
<echo message="my.test.key1: ${my.test.key1}" />
<echo message="my.test.key2: ${my.test.key2}" />

内容的提问来源于stack exchange，提问作者Yuki Yasha