通过tool.jar动态生成类并编译加载

类别:Java 点击:0 评论:0 推荐:

jdk\lib目录下的tool.jar包含了一个完整的java编译器包,利用它可以实现类文件的运行时动态生成并且编译加载。下面是一个例子:

import java.io.*; import java.util.*; import java.lang.reflect.*; public class MakeTodayClass { Date today = new Date(); String todayMillis = Long.toString(today.getTime()); String todayClass = "z_" + todayMillis; String todaySource = todayClass + ".java"; public static void main (String args[]){ MakeTodayClass mtc = new MakeTodayClass(); mtc.createIt(); if (mtc.compileIt()) { System.out.println("Running " + mtc.todayClass + ":\n\n"); mtc.runIt(); } else System.out.println(mtc.todaySource + " is bad."); } public void createIt() { try { FileWriter aWriter = new FileWriter(todaySource, true); aWriter.write("public class "+ todayClass + "{"); aWriter.write(" public void doit() {"); aWriter.write(" System.out.println(\""+todayMillis+"\");"); aWriter.write(" }}\n"); aWriter.flush(); aWriter.close(); } catch(Exception e){ e.printStackTrace(); } } public boolean compileIt() { String [] source = { new String(todaySource)}; ByteArrayOutputStream baos= new ByteArrayOutputStream(); new sun.tools.javac.Main(baos,source[0]).compile(source); // if using JDK >= 1.3 then use // public static int com.sun.tools.javac.Main.compile(source); return (baos.toString().indexOf("error")==-1); } public void runIt() { try { Class params[] = {}; Object paramsObj[] = {}; Class thisClass = Class.forName(todayClass); Object iClass = thisClass.newInstance(); Method thisMethod = thisClass.getDeclaredMethod("doit", params); thisMethod.invoke(iClass, paramsObj); } catch (Exception e) { e.printStackTrace(); } } }

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