java 不能直接修改windows系统的环境变量，需要借助JNI转为C++的接口，以调用windows系统的注册表
如其说修改环境变量，不如说修改注册表更准确些,因为是通过修改注册表来实现修改环境变量的；“环境变量”的键值所在位
置：HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session
Manager\Environment
Windows Registry API Native Interface下载地址
http://www.trustice.com/java/jnireg/index.shtml 下
registry-3.1.3.zip(包含源代码)。解开 registry-3.1.3.zip，在 bin 目录中可以看到两个文件
ICE_JNIRegistry.dll 和registry.jar，动态库就是本地代码实现。
1 package frame;
2
3 import java.io.BufferedReader;
4 import java.io.InputStreamReader;
5
6 import com.ice.jni.registry.RegStringValue;
7 import com.ice.jni.registry.Registry;
8 import com.ice.jni.registry.RegistryKey;
9
10 public class TestRegistry {
11
12 /**
13 * @param args
14 */
15 public static void main(String[] args) {
16 // TODO Auto-generated method stub
17 try {
18 //RegistryKey openPath1
19 // = Registry.HKEY_LOCAL_MACHINE.openSubKey("SYSTEM\\CurrentControlSet\\Control\\Session Manager\\Environment");
20 //String path_Old = openPath1.getStringValue("PAODING_DIC_HOME"); //获取原Path键值
21 //System.out.println(path_Old);
22 //System.out.println(System.getProperty("user.dir"));
23
24 RegistryKey openPath2
25 = Registry.HKEY_LOCAL_MACHINE.openSubKey("SYSTEM\\CurrentControlSet\\Control\\Session Manager");
26 RegistryKey subKey = openPath2.createSubKey("Environment", "");
27 subKey.setValue(new RegStringValue(subKey, "PAODING_DIC_HOME", "D:\\PaodingEnv\\Dic")); //修改Path键值
28 subKey.closeKey();
29 /*RegistryKey openPath2
30 = Registry.HKEY_LOCAL_MACHINE.openSubKey("SYSTEM\\CurrentControlSet\\Control\\Session Manager");
31
32 RegistryKey subKey = openPath2.createSubKey("Environment", "");
33 //定义Path所在目录的句柄（相当于在Session Manager路径下面，新建Environment文件夹，如果存在不改变已有的值。）
34 // String path_New = path_Old + ";" + "D:\\myTinoProject\\bingy";
35 String path_New = path_Old + "bin;";
36 subKey.setValue(new RegStringValue(subKey, "Path", path_New)); //修改Path键值
37 subKey.closeKey();
38 //查看进程的方法
39 String[] cmd = { "D:\\dfqd\\workspace\\tasklist" };
40 Process proc = Runtime.getRuntime().exec(cmd);
41 BufferedReader in = new BufferedReader(new InputStreamReader(proc.getInputStream()));
42 String string_Temp = in.readLine();
43 while (string_Temp != null) {
44 System.out.println(string_Temp);
45 string_Temp = in.readLine();
46 }
47 //删除explorer.exe进程
48 Process proc2 = Runtime.getRuntime().exec("D:\\dfqd\\workspace\\taskkill /F /IM explorer.exe");
49 Thread.sleep(500);
50 //重启explorer.exe进程
51 Process proc3 = Runtime.getRuntime().exec("explorer.exe");
52 System.out.println("=====SUCCESS=====");*/
53 }
54 catch (Exception e) {
55 e.printStackTrace();
56 }
57 }
58 }
59