如何从Java设置环境变量？

这是@ paul-blair转换为Java的答案的组合,其中包括由保罗布莱尔指出的一些清理以及似乎在@pushy的代码内部的一些错误,这些错误由@Edward Campbell和匿名组成.

我不能强调这个代码应该只用于测试多少,而且非常hacky.但是对于需要在测试中设置环境的情况,这正是我所需要的.

这还包括我的一些小修改,允许代码在运行的Windows上运行

java version "1.8.0_92"
Java(TM) SE Runtime Environment (build 1.8.0_92-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.92-b14, mixed mode)

以及运行的Centos

openjdk version "1.8.0_91"
OpenJDK Runtime Environment (build 1.8.0_91-b14)
OpenJDK 64-Bit Server VM (build 25.91-b14, mixed mode)

实施:

/**
 * Sets an environment variable FOR THE CURRENT RUN OF THE JVM
 * Does not actually modify the system's environment variables,
 *  but rather only the copy of the variables that java has taken,
 *  and hence should only be used for testing purposes!
 * @param key The Name of the variable to set
 * @param value The value of the variable to set
 */
@SuppressWarnings("unchecked")
public static  void setenv(final String key, final String value) {
    try {
        /// we obtain the actual environment
        final Class processEnvironmentClass = Class.forName("java.lang.ProcessEnvironment");
        final Field theEnvironmentField = processEnvironmentClass.getDeclaredField("theEnvironment");
        final boolean environmentAccessibility = theEnvironmentField.isAccessible();
        theEnvironmentField.setAccessible(true);

        final Map env = (Map) theEnvironmentField.get(null);

        if (SystemUtils.IS_OS_WINDOWS) {
            // This is all that is needed on windows running java jdk 1.8.0_92
            if (value == null) {
                env.remove(key);
            } else {
                env.put((K) key, (V) value);
            }
        } else {
            // This is triggered to work on openjdk 1.8.0_91
            // The ProcessEnvironment$Variable is the key of the map
            final Class variableClass = (Class) Class.forName("java.lang.ProcessEnvironment$Variable");
            final Method convertToVariable = variableClass.getMethod("valueOf", String.class);
            final boolean conversionVariableAccessibility = convertToVariable.isAccessible();
            convertToVariable.setAccessible(true);

            // The ProcessEnvironment$Value is the value fo the map
            final Class valueClass = (Class) Class.forName("java.lang.ProcessEnvironment$Value");
            final Method convertToValue = valueClass.getMethod("valueOf", String.class);
            final boolean conversionValueAccessibility = convertToValue.isAccessible();
            convertToValue.setAccessible(true);

            if (value == null) {
                env.remove(convertToVariable.invoke(null, key));
            } else {
                // we place the new value inside the map after conversion so as to
                // avoid class cast exceptions when rerunning this code
                env.put((K) convertToVariable.invoke(null, key), (V) convertToValue.invoke(null, value));

                // reset accessibility to what they were
                convertToValue.setAccessible(conversionValueAccessibility);
                convertToVariable.setAccessible(conversionVariableAccessibility);
            }
        }
        // reset environment accessibility
        theEnvironmentField.setAccessible(environmentAccessibility);

        // we apply the same to the case insensitive environment
        final Field theCaseInsensitiveEnvironmentField = processEnvironmentClass.getDeclaredField("theCaseInsensitiveEnvironment");
        final boolean insensitiveAccessibility = theCaseInsensitiveEnvironmentField.isAccessible();
        theCaseInsensitiveEnvironmentField.setAccessible(true);
        // Not entirely sure if this needs to be casted to ProcessEnvironment$Variable and $Value as well
        final Map cienv = (Map) theCaseInsensitiveEnvironmentField.get(null);
        if (value == null) {
            // remove if null
            cienv.remove(key);
        } else {
            cienv.put(key, value);
        }
        theCaseInsensitiveEnvironmentField.setAccessible(insensitiveAccessibility);
    } catch (final ClassNotFoundException | NoSuchMethodException | IllegalAccessException | InvocationTargetException e) {
        throw new IllegalStateException("Failed setting environment variable <"+key+"> to <"+value+">", e);
    } catch (final NoSuchFieldException e) {
        // we could not find theEnvironment
        final Map env = System.getenv();
        Stream.of(Collections.class.getDeclaredClasses())
                // obtain the declared classes of type $UnmodifiableMap
                .filter(c1 -> "java.util.Collections$UnmodifiableMap".equals(c1.getName()))
                .map(c1 -> {
                    try {
                        return c1.getDeclaredField("m");
                    } catch (final NoSuchFieldException e1) {
                        throw new IllegalStateException("Failed setting environment variable <"+key+"> to <"+value+"> when locating in-class memory map of environment", e1);
                    }
                })
                .forEach(field -> {
                    try {
                        final boolean fieldAccessibility = field.isAccessible();
                        field.setAccessible(true);
                        // we obtain the environment
                        final Map map = (Map) field.get(env);
                        if (value == null) {
                            // remove if null
                            map.remove(key);
                        } else {
                            map.put(key, value);
                        }
                        // reset accessibility
                        field.setAccessible(fieldAccessibility);
                    } catch (final ConcurrentModificationException e1) {
                        // This may happen if we keep backups of the environment before calling this method
                        // as the map that we kept as a backup may be picked up inside this block.
                        // So we simply skip this attempt and continue adjusting the other maps
                        // To avoid this one should always keep individual keys/value backups not the entire map
                        LOGGER.info("Attempted to modify source map: "+field.getDeclaringClass()+"#"+field.getName(), e1);
                    } catch (final IllegalAccessException e1) {
                        throw new IllegalStateException("Failed setting environment variable <"+key+"> to <"+value+">. Unable to access field!", e1);
                    }
                });
    }
    LOGGER.info("Set environment variable <"+key+"> to <"+value+">. Sanity Check: "+System.getenv(key));
}