java----动态编译

java执行外部程序的方式

1 Runtime

2 Process Builder

动态编译的两种做法：

-通过Runtime调用javac，启动新的进程去操作

Runtime run =Runtime.getRuntime();
Process process=run.exec("javac -cp  d:/myjava/  HelloWorld.java");

-通过JavaCompiler动态编译

public static void main(String[] args) throws IOException {
        //将本地文件进行编译
        JavaCompiler systemJavaCompiler = ToolProvider.getSystemJavaCompiler();
        int run = systemJavaCompiler.run(null, null, null, "C:\Users\zhengyan\Desktop\Test\src\main\java\com\zy\Test.java");
        System.out.println(run);

        //将一个字符串进行编译(使用IO流)
        String str = "public class T{
" +
                "	public void test(){}
" +
                "}";
        File file = new File("T.java");
        if (!file.exists()){
            file.createNewFile();
            FileOutputStream fileOutputStream = new FileOutputStream("T.java");
            fileOutputStream.write(str.getBytes());
        }
        run = systemJavaCompiler.run(null, null, null, "T.java");
        System.out.println(run);
    }

补充

public class T{
	public static void main(String[] args) {
		System.out.println("hellow");
	}
}

动态运行编译好的类的两种做法：

-通过Runtime.getRuntime/运行启动新的进程运行

    public static void main(String[] args) throws IOException {
        Runtime run =Runtime.getRuntime();
        Process process=run.exec("java -cp  /  T"); //可能用"/"不好使,我们把T.class复制到桌面
        //Process process=run.exec("java -cp  C:\Users\zhengyan\Desktop  T"); //可能用"/"不好使,我们把T.class复制到桌面
        //因为T程序需要输出内容,所以我们打印出来
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(process.getInputStream()));
        String info;
        while ((info=bufferedReader.readLine())!=null){
            System.out.println(info);
        }
        System.out.println("end");
    }

通过反射运行编译好的类

    public static void main(String[] args) throws IOException, ClassNotFoundException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        URL[] urls = new URL[] {new URL("file:/C:/Users/zhengyan/Desktop/")};
        URLClassLoader urlClassLoader = new URLClassLoader(urls);
        Class<?> t = urlClassLoader.loadClass("T"); //反射
        Method main = t.getMethod("main",String[].class);
        //静态方法不需要实例化 T 对象
        //main.invoke(Object object,Object... args);
        main.invoke(null,(Object)new String[]{"a","b"});
        //main.invoke(null,new String[]{"a","b"});
        //如果不强转Object,编译器会变成成main.invoke(null,"a","b"});
    }