java中创建进程

Java中提供了两种方法来启动其它进程：
方法一：
	Process process = new ProcessBuilder(cmd).start();
方法二：
	Process process = Runtime.getRuntime().exec(cmd);
	注意：底层也是调用方法一。


Process的waitFor()方法：
	说明：等待Process结束后返回Process的返回值，若Process一直未结束，则程序一直等待下去。
	分析：
		创建的新进程与jvm建立三个管道连接：标准输入流、标准输出流、标准错误输出流。
		若新进程不断向标准输入流、标准错误输出流写数据，而jvm不读取的话，则会导致缓冲区塞满而无法继续写数据，从而造成新进程一直不结束，最终导致调用waitFor()方法的线程阻塞。
	解决：
		jvm读取新进程写入缓存区的数据(即:标准输入流Process.getInputStream()、标准错误输出流Process.getErrorStream()中的数据)即可。
		eg：
			    // 打印进程的输出信息
	            List outputStr = IOUtils.readLines(process.getInputStream(), "UTF-8");
	            List errorOutputStr = IOUtils.readLines(process.getErrorStream(), "UTF-8");
	            LOGGER.info("=============new process output start =======");
	            LOGGER.info(outputStr.toString());
	            LOGGER.info("=============new process output end =======");
	            LOGGER.info("=============new process error output start =======");
	            LOGGER.info(errorOutputStr.toString());
	            LOGGER.info("=============new process error output end =======");

	相关源码：
	    /**
	     * Causes the current thread to wait, if necessary, until the process represented by this {@code Process} object has terminated.  
	     * This method returns immediately if the subprocess has already terminated.  
	     * If the subprocess has not yet terminated, the calling thread will be blocked until the subprocess exits.
	     */
	    public synchronized int waitFor() throws InterruptedException {
	        while (!hasExited) {
	            wait();
	        }
	        return exitcode;
	    }


	    /**
	     * Returns the input stream connected to the normal output of the subprocess.  
	     * The stream obtains data piped from the standard output of the process represented by this {@code Process} object.
	     */
	    public abstract InputStream getInputStream();


	    /**
	     * Returns the input stream connected to the error output of the subprocess. 
	     * The stream obtains data piped from the error output of the process represented by this {@code Process} object.
	     */
	    public abstract InputStream getErrorStream();


	    /**
	     * Returns the output stream connected to the normal input of the subprocess.  
	     * Output to the stream is piped into the standard input of the process represented by this {@code Process} object.
	     */
	    public abstract OutputStream getOutputStream();