77 lines
2.7 KiB
Java
77 lines
2.7 KiB
Java
package com.muyu.dynamicLoad;
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import javax.tools.JavaCompiler;
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import javax.tools.JavaFileObject;
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import javax.tools.StandardJavaFileManager;
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import javax.tools.ToolProvider;
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import java.io.IOException;
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import java.net.URL;
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import java.net.URLClassLoader;
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import java.util.Arrays;
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import java.util.HashMap;
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import java.util.Map;
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/**
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* @author qdm
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* @ClassName DynamicLoader
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*/
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public class DynamicLoader {
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/**
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* 通过类名和其代码（Java代码字符串），编译得到字节码，返回类名及其对应类的字节码，封装于Map中，值得注意的是，
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* 平常类中就编译出来的字节码只有一个类，但是考虑到内部类的情况， 会出现很多个类名及其字节码，所以用Map封装方便。
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*
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* @param javaName 类名
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* @param javaSrc Java源码
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* @return map
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*/
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public static Map<String, byte[]> compile(String javaName, String javaSrc) {
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// 调用java编译器接口
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JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
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StandardJavaFileManager stdManager = compiler
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.getStandardFileManager(null, null, null);
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try (MemoryJavaFileManager manager = new MemoryJavaFileManager(
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stdManager)) {
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@SuppressWarnings("static-access")
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JavaFileObject javaFileObject = manager.makeStringSource(javaName,
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javaSrc);
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JavaCompiler.CompilationTask task = compiler.getTask(null, manager,
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null, null, null, Arrays.asList(javaFileObject));
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if (task.call()) {
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return manager.getClassBytes();
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}
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} catch (IOException e) {
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e.printStackTrace();
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}
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return null;
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}
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/**
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* 先根据类名在内存中查找是否已存在该类，若不存在则调用 URLClassLoader的 defineClass方法加载该类
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* URLClassLoader的具体作用就是将class文件加载到jvm虚拟机中去
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*
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* @author Administrator
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*/
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public static class MemoryClassLoader extends URLClassLoader {
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Map<String, byte[]> classBytes = new HashMap<String, byte[]>();
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public MemoryClassLoader(Map<String, byte[]> classBytes) {
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super(new URL[0], MemoryClassLoader.class.getClassLoader());
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this.classBytes.putAll(classBytes);
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}
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@Override
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protected Class<?> findClass(String name)
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throws ClassNotFoundException {
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byte[] buf = classBytes.get(name);
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if (buf == null) {
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return super.findClass(name);
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}
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classBytes.remove(name);
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return defineClass(name, buf, 0, buf.length);
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}
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}
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}
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