尝试了上面pushy的答案，它在很大程度上起了作用。然而，在某些情况下，我会看到这个例外:

java.lang.String cannot be cast to java.lang.ProcessEnvironment$Variable

由于ProcessEnvironment的某些内部类的实现，当该方法被多次调用时就会发生这种情况。如果setEnv(..)方法被多次调用，当从theEnvironment映射中检索键时，它们现在是字符串(在第一次调用setEnv(…)时已作为字符串放入)，并且不能转换为映射的泛型类型Variable，这是ProcessEnvironment的私有内部类。

下面是一个固定版本(在Scala中)。希望将其应用到Java中并不太难。

def setEnv(newenv: java.util.Map[String, String]): Unit = {
  try {
    val processEnvironmentClass = JavaClass.forName("java.lang.ProcessEnvironment")
    val theEnvironmentField = processEnvironmentClass.getDeclaredField("theEnvironment")
    theEnvironmentField.setAccessible(true)

    val variableClass = JavaClass.forName("java.lang.ProcessEnvironment$Variable")
    val convertToVariable = variableClass.getMethod("valueOf", classOf[java.lang.String])
    convertToVariable.setAccessible(true)

    val valueClass = JavaClass.forName("java.lang.ProcessEnvironment$Value")
    val convertToValue = valueClass.getMethod("valueOf", classOf[java.lang.String])
    convertToValue.setAccessible(true)

    val sampleVariable = convertToVariable.invoke(null, "")
    val sampleValue = convertToValue.invoke(null, "")
    val env = theEnvironmentField.get(null).asInstanceOf[java.util.Map[sampleVariable.type, sampleValue.type]]
    newenv.foreach { case (k, v) => {
        val variable = convertToVariable.invoke(null, k).asInstanceOf[sampleVariable.type]
        val value = convertToValue.invoke(null, v).asInstanceOf[sampleValue.type]
        env.put(variable, value)
      }
    }

    val theCaseInsensitiveEnvironmentField = processEnvironmentClass.getDeclaredField("theCaseInsensitiveEnvironment")
    theCaseInsensitiveEnvironmentField.setAccessible(true)
    val cienv = theCaseInsensitiveEnvironmentField.get(null).asInstanceOf[java.util.Map[String, String]]
    cienv.putAll(newenv);
  }
  catch {
    case e : NoSuchFieldException => {
      try {
        val classes = classOf[java.util.Collections].getDeclaredClasses
        val env = System.getenv()
        classes foreach (cl => {
          if("java.util.Collections$UnmodifiableMap" == cl.getName) {
            val field = cl.getDeclaredField("m")
            field.setAccessible(true)
            val map = field.get(env).asInstanceOf[java.util.Map[String, String]]
            // map.clear() // Not sure why this was in the code. It means we need to set all required environment variables.
            map.putAll(newenv)
          }
        })
      } catch {
        case e2: Exception => e2.printStackTrace()
      }
    }
    case e1: Exception => e1.printStackTrace()
  }
}

这是@paul-blair的回答转换成Java的组合，其中包括paul blair指出的一些清理，以及@pushy的代码(由@Edward Campbell和anonymous组成)中似乎存在的一些错误。

我不能强调这段代码只应该在测试中使用，而且非常hack。但是对于在测试中需要环境设置的情况，这正是我所需要的。

这还包括我的一些小改动，允许代码在运行的两个Windows上工作

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)

和Centos一样

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)

实现:

/**
 * 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 <K,V> 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<K,V> env = (Map<K, V>) 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$Variable is the key of the map
            final Class<K> variableClass = (Class<K>) Class.forName("java.lang.ProcessEnvironment$Variable");
            final Method convertToVariable = variableClass.getMethod("valueOf", String.class);
            final boolean conversionVariableAccessibility = convertToVariable.isAccessible();
            convertToVariable.setAccessible(true);

            // The ProcessEnvironment$Value is the value fo the map
            final Class<V> valueClass = (Class<V>) Class.forName("java.lang.ProcessEnvironment$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<String, String> cienv = (Map<String, String>) 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<String, String> 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<String, String> map = (Map<String, String>) 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));
}

设置单个环境变量(基于Edward Campbell的回答):

public static void setEnv(String key, String value) {
    try {
        Map<String, String> env = System.getenv();
        Class<?> cl = env.getClass();
        Field field = cl.getDeclaredField("m");
        field.setAccessible(true);
        Map<String, String> writableEnv = (Map<String, String>) field.get(env);
        writableEnv.put(key, value);
    } catch (Exception e) {
        throw new IllegalStateException("Failed to set environment variable", e);
    }
}

用法:

首先，把这个方法放在任何你想要的类中，例如SystemUtil。然后静态调用它:

SystemUtil.setEnv("SHELL", "/bin/bash");

如果在此之后调用System.getenv("SHELL")，则会返回"/bin/bash"。

(是不是因为这是Java，所以我不应该做邪恶的、不可移植的、过时的事情，比如触摸我的环境?)

我认为你说到点子上了。

减轻负担的一个可能的方法是找出一种方法

void setUpEnvironment(ProcessBuilder builder) {
    Map<String, String> env = builder.environment();
    // blah blah
}

并在启动任何processbuilder之前通过它。

另外，您可能已经知道这一点，但是您可以使用同一个ProcessBuilder启动多个流程。因此，如果子流程是相同的，就不需要一遍又一遍地进行这个设置。

你可以使用-D将参数传递到你的初始java进程:

java -cp <classpath> -Dkey1=value -Dkey2=value ...

在Android上，界面是通过Libcore公开的。os作为一种隐藏的API。

Libcore.os.setenv("VAR", "value", bOverwrite);
Libcore.os.getenv("VAR"));

Libcore类和接口操作系统都是公开的。只有类声明缺失，需要显示给链接器。不需要将类添加到应用程序中，但是如果包含了类也无妨。

package libcore.io;

public final class Libcore {
    private Libcore() { }

    public static Os os;
}

package libcore.io;

public interface Os {
    public String getenv(String name);
    public void setenv(String name, String value, boolean overwrite) throws ErrnoException;
}