Java|Java Runtime的使用详解 JavaRuntime的使用详解

前言
1. shutdownhook
2. exec执行

2.1 常规命令执行
2.2 管道符
2.3源码分析

3. 总结

前言最近做项目框架，需要在框架结束的时候，关闭服务器连接，清除部分框架运行lock文件，这里就想到了shutdownhook，顺便学了学Runtime的使用

1. shutdownhook demo示例，证明在程序正常结束的时候会调用，如果kill -9 那肯定就不会调用了

public class ShutdownHookTest { public static void main(String[] args) {System.out.println("==============application start================"); Runtime.getRuntime().addShutdownHook(new Thread(()->{System.out.println("--------------hook 1----------------"); })); Runtime.getRuntime().addShutdownHook(new Thread(()->{System.out.println("--------------hook 2----------------"); })); System.out.println("==============application end================"); }}

正常运行结束，结果如下

==============application start================
==============application end================
--------------hook 1----------------
--------------hook 2----------------

Process finished with exit code 0

如果暂停，点击下图左下角的正方形红图标，停止正在运行的应用

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结果如下，shutdownhook已执行。

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shutdownhook可以处理程序正常结束的时候，删除文件，关闭连接等

2. exec执行
2.1 常规命令执行
demo示例如下，比如ls

public class ShutdownHookTest { public static void main(String[] args) throws InterruptedException, IOException {Process process = Runtime.getRuntime().exec("ls"); try (InputStream fis = process.getInputStream(); InputStreamReader isr = new InputStreamReader(fis); BufferedReader br = new BufferedReader(isr)) {String line; while ((line = br.readLine()) != null) {System.out.println(line); }}}}

结果如下

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而正常执行结果

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但是这个方法有远程执行风险，即在浏览器端通过这个方法执行特定指令，比如执行rm -rf *，结果就很……

2.2 管道符
但是遇见管道符之后就会失效，什么办法解决，sh -c，但是不能直接用，否则获取到的是TTY窗口信息

public static void main(String[] args) throws IOException {Process process = Runtime.getRuntime().exec("sh -c ps aux|grep java"); try (InputStream fis = process.getInputStream(); InputStreamReader isr = new InputStreamReader(fis); BufferedReader br = new BufferedReader(isr)) {String line; while ((line = br.readLine()) != null) {System.out.println(line); }}}

结果

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sh -c的参数要分离，不然runtime会认为是一个参数

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2.3源码分析
跟踪代码，使用ProcessImpl来执行指令

public Process exec(String[] cmdarray, String[] envp, File dir)throws IOException {return new ProcessBuilder(cmdarray).environment(envp).directory(dir).start(); }

ProcessBuilder

// Only for use by ProcessBuilder.start()static Process start(String[] cmdarray,java.util.Map environment,String dir,ProcessBuilder.Redirect[] redirects,boolean redirectErrorStream)throws IOException{assert cmdarray != null && cmdarray.length > 0; // Convert arguments to a contiguous block; it's easier to do// memory management in Java than in C.byte[][] args = new byte[cmdarray.length-1][]; int size = args.length; // For added NUL bytesfor (int i = 0; i < args.length; i++) {args[i] = cmdarray[i+1].getBytes(); size += args[i].length; }byte[] argBlock = new byte[size]; int i = 0; for (byte[] arg : args) {System.arraycopy(arg, 0, argBlock, i, arg.length); i += arg.length + 1; // No need to write NUL bytes explicitly} int[] envc = new int[1]; byte[] envBlock = ProcessEnvironment.toEnvironmentBlock(environment, envc); int[] std_fds; FileInputStreamf0 = null; FileOutputStream f1 = null; FileOutputStream f2 = null; try {if (redirects == null) {std_fds = new int[] { -1, -1, -1 }; } else {std_fds = new int[3]; if (redirects[0] == Redirect.PIPE)std_fds[0] = -1; else if (redirects[0] == Redirect.INHERIT)std_fds[0] = 0; else {f0 = new FileInputStream(redirects[0].file()); std_fds[0] = fdAccess.get(f0.getFD()); } if (redirects[1] == Redirect.PIPE)std_fds[1] = -1; else if (redirects[1] == Redirect.INHERIT)std_fds[1] = 1; else {f1 = new FileOutputStream(redirects[1].file(),redirects[1].append()); std_fds[1] = fdAccess.get(f1.getFD()); } if (redirects[2] == Redirect.PIPE)std_fds[2] = -1; else if (redirects[2] == Redirect.INHERIT)std_fds[2] = 2; else {f2 = new FileOutputStream(redirects[2].file(),redirects[2].append()); std_fds[2] = fdAccess.get(f2.getFD()); }} return new UNIXProcess(toCString(cmdarray[0]),argBlock, args.length,envBlock, envc[0],toCString(dir),std_fds,redirectErrorStream); } finally {// In theory, close() can throw IOException// (although it is rather unlikely to happen here)try { if (f0 != null) f0.close(); }finally {try { if (f1 != null) f1.close(); }finally { if (f2 != null) f2.close(); }}}}

new UNIXProcess 环境

/** * java.lang.Process subclass in the UNIX environment. * * @author Mario Wolczko and Ross Knippel. * @author Konstantin Kladko (ported to Linux and Bsd) * @author Martin Buchholz * @author Volker Simonis (ported to AIX) */final class UNIXProcess extends Process {

3. 总结 Runtime用处非常多，偏底层
比如gc调用