如何从Java中设置环境变量?我发现我可以使用ProcessBuilder为子流程做到这一点。不过，我有几个子流程要启动，所以我宁愿修改当前流程的环境，让子流程继承它。
有一个System.getenv(String)用于获取单个环境变量。我还可以使用System.getenv()获得完整环境变量集的Map。但是，在该Map上调用put()会抛出UnsupportedOperationException——显然，它们意味着环境是只读的。并且，没有System.setenv()。
那么，有没有办法在当前运行的进程中设置环境变量呢?如果有，怎么做?如果不是，理由是什么?(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?)如果不是，有什么好的建议来管理我将需要提供给几个子流程的环境变量更改吗?
当前回答
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()
}
}
其他回答
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()
}
}
如果你使用SpringBoot，你可以在下面的属性中添加指定环境变量:
was.app.config.properties.toSystemProperties
这是@pushy的邪恶答案的Kotlin邪恶版本=)
@Suppress("UNCHECKED_CAST")
@Throws(Exception::class)
fun setEnv(newenv: Map<String, String>) {
try {
val processEnvironmentClass = Class.forName("java.lang.ProcessEnvironment")
val theEnvironmentField = processEnvironmentClass.getDeclaredField("theEnvironment")
theEnvironmentField.isAccessible = true
val env = theEnvironmentField.get(null) as MutableMap<String, String>
env.putAll(newenv)
val theCaseInsensitiveEnvironmentField = processEnvironmentClass.getDeclaredField("theCaseInsensitiveEnvironment")
theCaseInsensitiveEnvironmentField.isAccessible = true
val cienv = theCaseInsensitiveEnvironmentField.get(null) as MutableMap<String, String>
cienv.putAll(newenv)
} catch (e: NoSuchFieldException) {
val classes = Collections::class.java.getDeclaredClasses()
val env = System.getenv()
for (cl in classes) {
if ("java.util.Collections\$UnmodifiableMap" == cl.getName()) {
val field = cl.getDeclaredField("m")
field.setAccessible(true)
val obj = field.get(env)
val map = obj as MutableMap<String, String>
map.clear()
map.putAll(newenv)
}
}
}
它至少在macOS Mojave上运行。
在需要为单元测试设置特定环境值的场景中使用，您可能会发现以下hack很有用。它将在JVM中更改环境变量(因此请确保在测试后重置所有更改)，但不会更改系统环境。
我发现Edward Campbell和anonymous的两个肮脏的黑客组合效果最好，因为一个在linux下不起作用，另一个在windows 7下也不起作用。所以为了获得一个多平台的邪恶黑客，我将它们结合起来:
protected static void setEnv(Map<String, String> newenv) throws Exception {
try {
Class<?> processEnvironmentClass = Class.forName("java.lang.ProcessEnvironment");
Field theEnvironmentField = processEnvironmentClass.getDeclaredField("theEnvironment");
theEnvironmentField.setAccessible(true);
Map<String, String> env = (Map<String, String>) theEnvironmentField.get(null);
env.putAll(newenv);
Field theCaseInsensitiveEnvironmentField = processEnvironmentClass.getDeclaredField("theCaseInsensitiveEnvironment");
theCaseInsensitiveEnvironmentField.setAccessible(true);
Map<String, String> cienv = (Map<String, String>) theCaseInsensitiveEnvironmentField.get(null);
cienv.putAll(newenv);
} catch (NoSuchFieldException e) {
Class[] classes = Collections.class.getDeclaredClasses();
Map<String, String> env = System.getenv();
for(Class cl : classes) {
if("java.util.Collections$UnmodifiableMap".equals(cl.getName())) {
Field field = cl.getDeclaredField("m");
field.setAccessible(true);
Object obj = field.get(env);
Map<String, String> map = (Map<String, String>) obj;
map.clear();
map.putAll(newenv);
}
}
}
}
这招很管用。完全归功于这些黑客的两位作者。
蒂姆·瑞安的回答对我很管用……但我希望它用于Groovy(例如Spock上下文)，并且simplissimo:
import java.lang.reflect.Field
def getModifiableEnvironmentMap() {
def unmodifiableEnv = System.getenv()
Class cl = unmodifiableEnv.getClass()
Field field = cl.getDeclaredField("m")
field.accessible = true
field.get(unmodifiableEnv)
}
def clearEnvironmentVars( def keys ) {
def savedVals = [:]
keys.each{ key ->
String val = modifiableEnvironmentMap.remove(key)
// thinking about it, I'm not sure why we need this test for null
// but haven't yet done any experiments
if( val != null ) {
savedVals.put( key, val )
}
}
savedVals
}
def setEnvironmentVars(Map varMap) {
modifiableEnvironmentMap.putAll(varMap)
}
// pretend existing Env Var doesn't exist
def PATHVal1 = System.env.PATH
println "PATH val1 |$PATHVal1|"
String[] keys = ["PATH", "key2", "key3"]
def savedVars = clearEnvironmentVars(keys)
def PATHVal2 = System.env.PATH
println "PATH val2 |$PATHVal2|"
// return to reality
setEnvironmentVars(savedVars)
def PATHVal3 = System.env.PATH
println "PATH val3 |$PATHVal3|"
println "System.env |$System.env|"
// pretend a non-existent Env Var exists
setEnvironmentVars( [ 'key4' : 'key4Val' ])
println "key4 val |$System.env.key4|"
