最近專案中需要在在java中執行shell命令，用了最常見方式，程式碼如下:

public class ShellUtil {
    public static String runShell(String shStr) throws Exception {

        Process process;
        process = Runtime.getRuntime().exec(new String[]{"/bin/sh","-c",shStr});
        process.waitFor();
        BufferedReader read = new BufferedReader(new
 
 InputStreamReader(process.getInputStream()));
        String line = null;
        String result = "";
        while ((line = read.readLine())!=null){
            result+=line;
        }
        return result;
    }
}

在呼叫時如下呼叫：

public class ExecuteShell {
    public static void main (String[] args){
        String command = "some command"
 
;
        String message = ShellUtil.runShell(command);
        System.out.println(message);
    }
}

如果你要同時執行兩個命令或者多個命令的情況下，那麼呼叫就會如下所示：

public class ExecuteShell {
    public static void main (String[] args){
        String command1 = "some command";
        String command2 = "some command";
        String message1 = ShellUtil.runShell(command1);
        String message2 = ShellUtil.runShell(command2);
        System.out
 
.println(message1);
        System.out.println(message2);
    }
}

當時為了節約效能，改為如下形式：

public class ExecuteShell {
    public static void main (String[] args){
        String command1 = "some command";
        String command2 = "some command";
        String command = command1 + " && " + command2;
        String message = ShellUtil.runShell(command);
        System.out.println(message);
    }
}

本以為會取巧一下，但是實際結果為，都不會執行了，即整個返回為空，第一條和第二條都沒有執行。

解決方案

按照上述的方案將程式碼改為

public class ShellUtil {

    private static Logger logger = LoggerFactory.getLogger(ShellUtil.class);
    public static String runShell(String shStr) throws Exception {

        Process process;
        process = Runtime.getRuntime().exec(new String[]{"/bin/sh","-c",shStr});
        process.waitFor();
        BufferedReader read = new BufferedReader(new InputStreamReader(process.getInputStream()));
        String line = null;
        String result = "";
        while ((line = read.readLine())!=null){
            result+=line;
        }
        return result;
    }
}

即將Runtime.getRuntime().exec("command"); 改為 Runtime.getRuntime().exec(new String[]{"/bin/sh","-c","command"});

注意：如果是windows作業系統要改為Runtime.getRuntime().exec(new String[]{"**cmd** exe","-c","command"});

至此，問題解決。

原理解析：（待補充- -）