Java?Runtime的使用詳解

更新時間：2021年12月15日 15:04:15 作者：fenglllle

這篇文章主要介紹了Java?Runtime的使用詳解，具有很好的參考價值，希望對大家有所幫助。如有錯誤或未考慮完全的地方，望不吝賜教

前言

最近做項(xiàng)目框架，需要在框架結(jié)束的時候，關(guān)閉服務(wù)器連接，清除部分框架運(yùn)行l(wèi)ock文件，這里就想到了shutdownhook，順便學(xué)了學(xué)Runtime的使用

1. shutdownhook

demo示例，證明在程序正常結(jié)束的時候會調(diào)用，如果kill -9 那肯定就不會調(diào)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================");
    }
}

正常運(yùn)行結(jié)束，結(jié)果如下

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

Process finished with exit code 0

如果暫停，點(diǎn)擊下圖左下角的正方形紅圖標(biāo)，停止正在運(yùn)行的應(yīng)用

結(jié)果如下，shutdownhook已執(zhí)行。

shutdownhook可以處理程序正常結(jié)束的時候，刪除文件，關(guān)閉連接等

2. exec執(zhí)行

2.1 常規(guī)命令執(zhí)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);
            }
        }
    }
}

結(jié)果如下

而正常執(zhí)行結(jié)果

但是這個方法有遠(yuǎn)程執(zhí)行風(fēng)險，即在瀏覽器端通過這個方法執(zhí)行特定指令，比如執(zhí)行rm -rf *，結(jié)果就很……

2.2 管道符

但是遇見管道符之后就會失效，什么辦法解決，sh -c，但是不能直接用，否則獲取到的是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);
            }
        }
    }

結(jié)果??

sh -c的參數(shù)要分離，不然runtime會認(rèn)為是一個參數(shù)

2.3源碼分析

跟蹤代碼，使用ProcessImpl來執(zhí)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<String,String> 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 環(huán)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 {