Jdk19 动态编译 Java源码为 Class 文件

一.背景

1.Jdk 版本

版本查看命令：java -version

2.需求

本来想看下项目热部署的实现，比如 SpringBoot 不停机热加载 Jar 实现功能修改；后来看到 Jdk 支持源码动态编译，如果可以实现，那么就可以在线直接修改代码，再利用 SpringBoot 管理起来，替换旧的 Bean，实现功能修改。可能实际应用场景不多，可以做应急修改，线上服务最终还是需要把修改后的代码重新部署更为稳妥。

其实动态修改代码还可以通过 Arthas 实现，包括反编译、编译等更多功能

二.Java 源码动态编译实现

源码编译需要用到的关键类：

类	说明
JavaCompiler	编译器 ToolProvider.getSystemJavaCompiler();
SimpleJavaFileObject	文件对象类，可以表示源码、类文件
ClassLoader	顶层类加载器，抽象类
ForwardingJavaFileManager	文件管理器

项目结构如图

1.Maven 依赖

暂时只是一个 Maven 项目，未引入其他依赖

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>org.example</groupId><artifactId>DynamicDemo</artifactId><version>1.0-SNAPSHOT</version><properties><maven.compiler.source>19</maven.compiler.source><maven.compiler.target>19</maven.compiler.target><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding></properties></project>

2.源码包装类

基于 SimpleJavaFileObject 扩展，用于封装类名、源码信息

package org.example.demo.util;import javax.tools.SimpleJavaFileObject;
import java.io.IOException;
import java.net.URI;/*** @author moon* @date 2023-02-15 20:32* @since 1.8*/
public class CustomSourceCode extends SimpleJavaFileObject {/*** 类名称*/private String className;/*** 类源码*/private String contents;/*** 源码初始化* @param className* @param contents*/public CustomSourceCode(String className, String contents) {super(URI.create("string:///" + className.replace('.', '/')+ Kind.SOURCE.extension), Kind.SOURCE);this.contents = contents;this.className = className;}/*** 获取类名* @return*/public String getClassName() {return className;}/*** 源码字符序列* @param ignoreEncodingErrors ignore encoding errors if true* @return* @throws IOException*/public CharSequence getCharContent(boolean ignoreEncodingErrors)throws IOException {return contents;}
}

3.Java 文件对象封装类

基于 SimpleJavaFileObject 实现，封装了类名、类字节输出流信息

package org.example.demo.util;import javax.tools.SimpleJavaFileObject;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.URI;
import java.net.URISyntaxException;/*** @author moon* @date 2023-02-15 20:52* @since 1.8*/
public class CustomJavaFileObject extends SimpleJavaFileObject {/*** 类名称*/private String className;/*** 输出的字节码流*/private ByteArrayOutputStream toByteArray = new ByteArrayOutputStream();/*** Construct a SimpleJavaFileObject of the given kind and with the* given URI.** @param className*/public CustomJavaFileObject(String className) throws URISyntaxException {super(new URI(className), Kind.CLASS);this.className = className;}@Overridepublic OutputStream openOutputStream() throws IOException {return toByteArray;}/*** 获取类名* @return*/public String getClassName() {return className;}/*** 获取字节信息* @return*/public byte[] getByteCode() {return toByteArray.toByteArray();}
}

4.文件管理器封装类

package org.example.demo.util;import javax.tools.FileObject;
import javax.tools.ForwardingJavaFileManager;
import javax.tools.JavaFileManager;
import javax.tools.JavaFileObject;/*** @author moon* @date 2023-02-15 20:00* @since 1.8*/
public class CustomJavaFileManager extends ForwardingJavaFileManager<JavaFileManager> {/*** 自定义类加载器*/private CustomClassLoader loader;/*** 初始化* @param fileManager* @param loader*/protected CustomJavaFileManager(JavaFileManager fileManager, CustomClassLoader loader) {super(fileManager);this.loader = loader;}@Overridepublic JavaFileObject getJavaFileForOutput(JavaFileManager.Location location, String className,JavaFileObject.Kind kind, FileObject sibling) {try {CustomJavaFileObject innerClass = new CustomJavaFileObject(className);loader.addJavaCode(innerClass);return innerClass;} catch (Exception e) {throw new RuntimeException("exception when creating in-memory output stream for  " + className, e);}}@Overridepublic ClassLoader getClassLoader(JavaFileManager.Location location) {return loader;}}

5.类加载器

用于从 CustomJavaFileObject 获取字节流，并通过 ClassLoader.defineClass 生成类

package org.example.demo.util;import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;/*** @author moon* @date 2023-02-15 20:50* @since 1.8*/
public class CustomClassLoader extends ClassLoader{/*** 缓存源代码对象*/private Map<String, CustomJavaFileObject> fileCacheMap = new ConcurrentHashMap<>(16);/*** 初始化类加载器* @param parent*/public CustomClassLoader(ClassLoader parent) {super(parent);}/*** 添加源码缓存* @param obj*/public void addJavaCode(CustomJavaFileObject obj) {fileCacheMap.put(obj.getName(), obj);}/*** 获取类* @param className*          The <a href="#binary-name">binary name</a> of the class** @return* @throws ClassNotFoundException*/@Overrideprotected Class<?> findClass(String className) throws ClassNotFoundException {if (fileCacheMap.containsKey(className)){byte[] byteCode = fileCacheMap.get(className).getByteCode();return defineClass(className, byteCode, 0, byteCode.length);} else {return super.findClass(className);}}
}

6.类编译器

简要说明一下调用流程：读取源码 -> 编译 -> 加载为 Class => 构建对象及使用

package org.example.demo.util;import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;/*** @author moon* @date 2023-02-15 20:50* @since 1.8*/
public class CustomClassLoader extends ClassLoader{/*** 缓存源代码对象*/private Map<String, CustomJavaFileObject> fileCacheMap = new ConcurrentHashMap<>(16);/*** 初始化类加载器* @param parent*/public CustomClassLoader(ClassLoader parent) {super(parent);}/*** 添加源码缓存* @param obj*/public void addJavaCode(CustomJavaFileObject obj) {fileCacheMap.put(obj.getName(), obj);}/*** 获取类* @param className*          The <a href="#binary-name">binary name</a> of the class** @return* @throws ClassNotFoundException*/@Overrideprotected Class<?> findClass(String className) throws ClassNotFoundException {if (fileCacheMap.containsKey(className)){byte[] byteCode = fileCacheMap.get(className).getByteCode();return defineClass(className, byteCode, 0, byteCode.length);} else {return super.findClass(className);}}
}

三.动态编译测试

1.普通测试类

定义一个普通测试类，包含：有、无参构造初始化，有、无参方法调用

用户积分器

package org.example.demo.common;public class UserSort {private String name;private int score;public UserSort (){}public UserSort (String name, int sort){this.name = name;this.score = sort;}public void reset(){this.score = 0;System.out.println("姓名: " + this.name + " 积分重置: " + this.score);}public void insert(int score){this.score += score;System.out.println("姓名: " + this.name + " 加分结果: " + this.score);}public void reduce(int score){this.score -= score;System.out.println("姓名: " + this.name + " 减分结果: " + this.score);}
}

封装一个静态方法：

public static void commonClass(CustomClassCompiler compiler) throws Exception{String sourceCode = "package org.example.demo.common;\n" +"\n" +"public class UserSort {\n" +"\n" +"    private String name;\n" +"    private int score;\n" +"\n" +"    public UserSort (){\n" +"    }\n" +"\n" +"    public UserSort (String name, int sort){\n" +"        this.name = name;\n" +"        this.score = sort;\n" +"    }\n" +"\n" +"    public void reset(){\n" +"        this.score = 0;\n" +"        System.out.println(\"姓名: \" + this.name + \" 积分重置: \" + this.score);\n" +"    }\n" +"\n" +"    public void insert(int score){\n" +"        this.score += score;\n" +"        System.out.println(\"姓名: \" + this.name + \" 加分结果: \" + this.score);\n" +"    }\n" +"\n" +"    public void reduce(int score){\n" +"        this.score -= score;\n" +"        System.out.println(\"姓名: \" + this.name + \" 减分结果: \" + this.score);\n" +"    }\n" +"}";String className = "org.example.demo.common.UserSort";compiler.addSource(className, sourceCode);compiler.compile(className);Class<?> clazz = compiler.getClassByName(className);System.out.println("无参构造及重置分数-----------------------");Object object = clazz.getDeclaredConstructor().newInstance();Method method = clazz.getDeclaredMethod("reset");method.invoke(object);System.out.println("有参构造及重置分数-----------------------");object = clazz.getDeclaredConstructor(String.class,int.class).newInstance("张三",0);method.invoke(object);System.out.println("加分-----------------------------------");method = clazz.getDeclaredMethod("insert",int.class);method.invoke(object,10);System.out.println("减分-----------------------------------");method = clazz.getDeclaredMethod("reduce",int.class);method.invoke(object,2);}

2.接口实现类

定义一个处理器接口，用于处理数据

package org.example.demo.handler;/*** @author moon* @date 2023-02-15 20:55* @since 1.8*/
public interface BaseHandler {/*** 处理器* @param content*/void deal(String content);
}

封装一个静态方法，实现类不再单独贴出，简单加了个打印，输出【春江花月夜】

public static void interfaceClass(CustomClassCompiler compiler) throws Exception {String sourceCode = "package com.demo.handler;\n" +"import org.example.demo.handler.BaseHandler;\n" +"public class DynamicHandler implements BaseHandler {\n" +"    \n" +"    @Override\n" +"    public void deal(String content) {\n" +"        System.out.println(content);\n" +"    }\n" +"}";String className = "com.demo.handler.DynamicHandler";compiler.addSource(className, sourceCode);compiler.compile(className);BaseHandler handler = (BaseHandler) compiler.getClassByName(className).getDeclaredConstructor().newInstance();handler.deal("春江花月夜");}

3.测试

在 App 类内直接定义一个 main 方法，调用上面两个静态方法

package org.example.demo;import org.example.demo.handler.BaseHandler;
import org.example.demo.util.CustomClassCompiler;import java.lang.reflect.Method;/*** @author moon* @date 2023-02-15 20:42* @since 1.8*/
public class App {public static void main(String[] args) throws Exception {CustomClassCompiler compiler = CustomClassCompiler.newInstance(null);commonClass(compiler);System.out.println("\n--------------------------------------------------\n");interfaceClass(compiler);}//TODO 静态方法 commonClass//TODO 静态方法 interfaceClass}

调用效果如下：

四.用动态编译 Class 替换 SpringBoot 的 Bean（未完）

未完待续 . . .