Java Runtime的使用方法是什么

这篇文章将为大家详细讲解有关Java Runtime的使用方法是什么，文章内容质量较高，因此小编分享给大家做个参考，希望大家阅读完这篇文章后对相关知识有一定的了解。

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

结果如下，shutdownhook已执行。

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

而正常执行结果

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????

sh -c的参数要分离，不然runtime会认为是一个参数

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 bytes        for (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;         FileInputStream  f0 = 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

加载jar文件

Runtime功能强大，但需要合理利用，很多攻击是通过Runtime执行的漏洞

但是使用shutdownhook还是很方便的，用来做停止任务的后续处理。

关于Java Runtime的使用方法是什么就分享到这里了，希望以上内容可以对大家有一定的帮助，可以学到更多知识。如果觉得文章不错，可以把它分享出去让更多的人看到。