java 热编译，热加载

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一. 热编译

package com.lucain.dynamic;import sun.applet.AppletClassLoader;import sun.misc.Launcher;import javax.tools.JavaCompiler;import javax.tools.StandardJavaFileManager;import javax.tools.ToolProvider;import java.io.File;import java.io.FileWriter;import java.io.IOException;import java.io.Writer;import java.lang.reflect.Method;import java.util.Arrays;/** * Created by luxian.zhang on 2017/7/27. */public class Test {    /**     * 创建java文件     * @author Lucian     */    public static File generateJava() throws Exception{        // 1.创建需要动态编译的代码字符串        String nr = "\r\n"; //回车        String source = "package com.lucian; " + nr +                " public class  Hello{" + nr +                " public void hello(){" + nr +                " System.out.println(\"HelloWorld! 1\");" + nr +                " }" + nr +                " }";        File dir = new File(CustomizationClassLoader.sourcePath);        if(!dir.exists()){            dir.mkdirs();        }        File file = new File(dir,"Hello.java");        Writer writer = new FileWriter(file);        try {            writer.write(source);        } catch (IOException e) {            e.printStackTrace();        } finally {            writer.flush();            writer.close();        }        return file;    }    /**     * 编译java文件     */    public static void compilerJava(File file) throws Exception{        // 取得当前系统的编译器        JavaCompiler javaCompiler = ToolProvider.getSystemJavaCompiler();        //获取一个文件管理器        StandardJavaFileManager javaFileManager = javaCompiler.getStandardFileManager(null, null, null);        try {            //文件管理器与文件连接起来            Iterable it = javaFileManager.getJavaFileObjects(file);            File dir = new File(CustomizationClassLoader.classPath);            if(!dir.exists()){                dir.mkdirs();            }            //创建编译任务            JavaCompiler.CompilationTask  task = javaCompiler.getTask(null, javaFileManager, null, Arrays.asList("-d", CustomizationClassLoader.classPath), null, it);            //执行编译            task.call();        } catch (Exception e) {            e.printStackTrace();        } finally {            javaFileManager.close();        }    }    public static void main(String[] args) throws Exception{        compilerJava(generateJava());        CustomizationClassLoader classLoader = new CustomizationClassLoader();        Class cl = classLoader.loadClass("com.lucian.Hello");        Object obj = cl.newInstance();        Method helloMethod = cl.getMethod("hello", null);        helloMethod.invoke(obj, null);    }}

二. 热加载

自定义类加载器，实现热加载

package com.lucain.dynamic;import java.io.FileInputStream;/** * Created by luxian.zhang on 2017/7/27. */public class CustomizationClassLoader extends ClassLoader{    public static String classPath;    public static String sourcePath;    static {        classPath = System.getProperty("user.dir") + "/temp/class";        sourcePath = System.getProperty("user.dir")+"/temp/source";    }    @Override    protected Class<?> findClass(String name) throws ClassNotFoundException {        try {            byte[] data = loadByte(name);            return defineClass(name, data, 0, data.length);        } catch (Exception e) {            e.printStackTrace();            throw new ClassNotFoundException();        }    }    /**     * 加载class文件，转换为字节数组     */    private byte[] loadByte(String name) throws Exception {        name = name.replaceAll("\\.", "/");        FileInputStream fis = new FileInputStream(classPath + "/" + name                + ".class");        int len = fis.available();        byte[] data = new byte[len];        fis.read(data);        fis.close();        return data;    }}

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