也许是为了营造JVM就是操作系统平台的气氛,抑或是为了强调Java的平台无关性,不知几时起Java已经把System.getenv(String)函数废弃了。所以一般来说Java只能获取它自己定义的一些变量,而无法与操作系统的环境变量交互,只能在运行靠java的“-D”参数来设置要传递给它的一些变量。
所以唯一的办法只能先判断操作系统,然后用操作系统的命令来调出环境变量列表,设法获得该输出列表。下面转载来自http://www.rgagnon.com/javadetails/java-0150.html的一个范例:
import java.io.*;
import java.util.*;
public class ReadEnv {
public static Properties getEnvVars() throws Throwable {
Process p = null;
Properties envVars = new Properties();
Runtime r = Runtime.getRuntime();
String OS = System.getProperty("os.name").toLowerCase();
// System.out.println(OS);
if (OS.indexOf("windows 9") > -1) {
p = r.exec( "command.com /c set" );
}
else if ( (OS.indexOf("nt") > -1)
|| (OS.indexOf("windows 20") > -1 )
|| (OS.indexOf("windows xp") > -1) ) {
// thanks to JuanFran for the xp fix!
p = r.exec( "cmd.exe /c set" );
}
else {
// our last hope, we assume Unix (thanks to H. Ware for the fix)
p = r.exec( "env" );
}
BufferedReader br = new BufferedReader
( new InputStreamReader( p.getInputStream() ) );
String line;
while( (line = br.readLine()) != null ) {
int idx = line.indexOf( '=' );
String key = line.substring( 0, idx );
String value = line.substring( idx+1 );
envVars.setProperty( key, value );
// System.out.println( key + " = " + value );
}
return envVars;
}
public static void main(String args[]) {
try {
Properties p = ReadEnv.getEnvVars();
System.out.println("the current value of TEMP is : " +
p.getProperty("TEMP"));
}
catch (Throwable e) {
e.printStackTrace();
}
}
}
import java.util.*;
public class ReadEnv {
public static Properties getEnvVars() throws Throwable {
Process p = null;
Properties envVars = new Properties();
Runtime r = Runtime.getRuntime();
String OS = System.getProperty("os.name").toLowerCase();
// System.out.println(OS);
if (OS.indexOf("windows 9") > -1) {
p = r.exec( "command.com /c set" );
}
else if ( (OS.indexOf("nt") > -1)
|| (OS.indexOf("windows 20") > -1 )
|| (OS.indexOf("windows xp") > -1) ) {
// thanks to JuanFran for the xp fix!
p = r.exec( "cmd.exe /c set" );
}
else {
// our last hope, we assume Unix (thanks to H. Ware for the fix)
p = r.exec( "env" );
}
BufferedReader br = new BufferedReader
( new InputStreamReader( p.getInputStream() ) );
String line;
while( (line = br.readLine()) != null ) {
int idx = line.indexOf( '=' );
String key = line.substring( 0, idx );
String value = line.substring( idx+1 );
envVars.setProperty( key, value );
// System.out.println( key + " = " + value );
}
return envVars;
}
public static void main(String args[]) {
try {
Properties p = ReadEnv.getEnvVars();
System.out.println("the current value of TEMP is : " +
p.getProperty("TEMP"));
}
catch (Throwable e) {
e.printStackTrace();
}
}
}