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

Kotlin中的一个版本,在这个算法中,我创建了一个装饰器,允许您从环境中设置和获取变量。

import java.util.Collections
import kotlin.reflect.KProperty
​
class EnvironmentDelegate {
    operator fun getValue(thisRef: Any?, property: KProperty<*>): String {
        return System.getenv(property.name) ?: "-"
    }
​
    operator fun setValue(thisRef: Any?, property: KProperty<*>, value: String) {
        val key = property.name
​
        val classes: Array<Class<*>> = Collections::class.java.declaredClasses
        val env = System.getenv()
​
        val cl = classes.first { "java.util.Collections\$UnmodifiableMap" == it.name }
​
        val field = cl.getDeclaredField("m")
        field.isAccessible = true
        val obj = field[env]
        val map = obj as MutableMap<String, String>
        map.putAll(mapOf(key to value))
    }
}
​
class KnownProperties {
    var JAVA_HOME: String by EnvironmentDelegate()
    var sample: String by EnvironmentDelegate()
}
​
fun main() {
    val knowProps = KnownProperties()
    knowProps.sample = "2"
​
    println("Java Home: ${knowProps.JAVA_HOME}")
    println("Sample: ${knowProps.sample}")
}

其他回答

如果您像我一样在测试中遇到这个问题,并且正在使用Junit5,那么Junit-pioneer提供了非常有用的注释。maven版本

例子:

@Test
@SetEnvironmentVariable(key = "some variable",value = "new value")
void test() {
    assertThat(System.getenv("some variable")).
        isEqualTo("new value");
}

怎么推荐都不为过。

// this is a dirty hack - but should be ok for a unittest.
private void setNewEnvironmentHack(Map<String, String> newenv) throws Exception
{
  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.clear();
  env.putAll(newenv);
  Field theCaseInsensitiveEnvironmentField = processEnvironmentClass.getDeclaredField("theCaseInsensitiveEnvironment");
  theCaseInsensitiveEnvironmentField.setAccessible(true);
  Map<String, String> cienv = (Map<String, String>) theCaseInsensitiveEnvironmentField.get(null);
  cienv.clear();
  cienv.putAll(newenv);
}

基于@pushy回答的Jython变体,适用于windows。

def set_env(newenv):
    from java.lang import Class
    process_environment = Class.forName("java.lang.ProcessEnvironment")
    environment_field =  process_environment.getDeclaredField("theEnvironment")
    environment_field.setAccessible(True)
    env = environment_field.get(None)
    env.putAll(newenv)
    invariant_environment_field = process_environment.getDeclaredField("theCaseInsensitiveEnvironment");
    invariant_environment_field.setAccessible(True)
    invevn = invariant_environment_field.get(None)
    invevn.putAll(newenv)

用法:

old_environ = dict(os.environ)
old_environ['EPM_ORACLE_HOME'] = r"E:\Oracle\Middleware\EPMSystem11R1"
set_env(old_environ)

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 ...

Kotlin中的一个版本,在这个算法中,我创建了一个装饰器,允许您从环境中设置和获取变量。

import java.util.Collections
import kotlin.reflect.KProperty
​
class EnvironmentDelegate {
    operator fun getValue(thisRef: Any?, property: KProperty<*>): String {
        return System.getenv(property.name) ?: "-"
    }
​
    operator fun setValue(thisRef: Any?, property: KProperty<*>, value: String) {
        val key = property.name
​
        val classes: Array<Class<*>> = Collections::class.java.declaredClasses
        val env = System.getenv()
​
        val cl = classes.first { "java.util.Collections\$UnmodifiableMap" == it.name }
​
        val field = cl.getDeclaredField("m")
        field.isAccessible = true
        val obj = field[env]
        val map = obj as MutableMap<String, String>
        map.putAll(mapOf(key to value))
    }
}
​
class KnownProperties {
    var JAVA_HOME: String by EnvironmentDelegate()
    var sample: String by EnvironmentDelegate()
}
​
fun main() {
    val knowProps = KnownProperties()
    knowProps.sample = "2"
​
    println("Java Home: ${knowProps.JAVA_HOME}")
    println("Sample: ${knowProps.sample}")
}