采用ASM动态生成set和get方法

ASM 功能强大，采用指令操纵class文件，可以生成你所需的class文件。

package asm.model;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.net.URI;

import org.apache.commons.lang.StringUtils;
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.Type;


public class DynaModelClassLoader extends ClassLoader implements Opcodes {

public Class getIntModelClass(String className, String[] fields)
throws IllegalArgumentException, SecurityException,
IllegalAccessException, InvocationTargetException, IOException {
ClassWriter cw = new ClassWriter(0);
Class exampleClass;
cw.visit(V1_1, ACC_PUBLIC, className, null, "java/lang/Object", null);
// creates a MethodWriter for the (implicit) constructor
MethodVisitor mv = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null,
null);
// pushes the 'this' variable
mv.visitVarInsn(ALOAD, 0);
// invokes the super class constructor
mv.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V");
mv.visitInsn(RETURN);
// this code uses a maximum of one stack element and one local
// variable
mv.visitMaxs(1, 1);
mv.visitEnd();
// fields = new String[]{"dept1S", "dept2S", "dept3S", "dept4S",
// "dept5S"};
for (int i = 0; i < fields.length; i++) {
String field = fields[i];
String setMd = "set" + StringUtils.capitalize(field);
String getMd = "get" + StringUtils.capitalize(field);
cw.visitField(ACC_PRIVATE, field, "I", null, new Integer(0))
.visitEnd();// int dept1S=0;

mv = cw.visitMethod(ACC_PUBLIC, getMd, "()I", null, null);
mv.visitCode();
mv.visitVarInsn(ALOAD, 0);
mv.visitFieldInsn(GETFIELD, className, field, "I");
mv.visitInsn(IRETURN);
mv.visitMaxs(1, 1);
// mw.visitInsn(RETURN);
// this code uses a maximum of two stack elements and two local
// variables
mv.visitEnd();
cw.visitEnd();

mv = cw.visitMethod(ACC_PUBLIC, setMd, "(I)V", null, null);
mv.visitCode();
mv.visitVarInsn(ALOAD, 0);
mv.visitVarInsn(ILOAD, 1);
mv.visitFieldInsn(PUTFIELD, className, field, "I");
mv.visitInsn(RETURN);
mv.visitMaxs(2, 2);
// mw.visitInsn(RETURN);
// this code uses a maximum of two stack elements and two local
// variables
mv.visitEnd();
}
String[] strs = new String[]{"code"};
for (int i = 0; i < strs.length; i++) {
String setMd = "set" + StringUtils.capitalize(strs[i]);
String getMd = "get" + StringUtils.capitalize(strs[i]);
cw.visitField(ACC_PRIVATE, strs[i], "Ljava/lang/String;", null,
null).visitEnd();// int dept1S=0;

mv = cw.visitMethod(ACC_PUBLIC, getMd, "()Ljava/lang/String;", null,
null);
mv.visitCode();
mv.visitVarInsn(ALOAD, 0);
mv
.visitFieldInsn(GETFIELD, className, strs[i],
"Ljava/lang/String;");
mv.visitInsn(ARETURN);
mv.visitMaxs(1, 1);
mv.visitEnd();
cw.visitEnd();

mv = cw.visitMethod(ACC_PUBLIC, setMd, "(Ljava/lang/String;)V",
null, null);
mv.visitCode();
mv.visitVarInsn(ALOAD, 0);
mv.visitVarInsn(ALOAD, 1);
mv
.visitFieldInsn(PUTFIELD, className, strs[i],
"Ljava/lang/String;");
mv.visitMaxs(2, 2);
mv.visitInsn(RETURN);
mv.visitEnd();
}

cw.visitEnd();
byte[] code = cw.toByteArray();
// // 把编译好的.class文件放到他对应的包里面
// 写.class"WebRoot/WEB-INF/classes/" +
FileOutputStream fos = new FileOutputStream("bin/"+className + ".class");
fos.write(code);
fos.close();
String classFile = className.replaceAll("/", ".");
System.out.println(classFile);

DynaModelClassLoader loader = new DynaModelClassLoader();
exampleClass = loader.defineClass(classFile, code, 0, code.length);
// exampleClass.getMethods()[0].invoke(null, new Object[] { null });
return exampleClass;
}



// /* (non-Javadoc)
// * @see java.lang.ClassLoader#findClass(java.lang.String)
// */
// protected Class findClass(String name) throws ClassNotFoundException {
// // TODO Auto-generated method stub
// return super.findClass(name);
// }
  
public void testClass(String name, String[] fields) throws InstantiationException, NoSuchMethodException, IllegalArgumentException, SecurityException, IllegalAccessException, InvocationTargetException, IOException{
Class cls = null;
String clsName=name.replaceAll("/",".");
Class cls2=getIntModelClass(name,fields);
Object wlo2 = cls2.newInstance();
cls = findLoadedClass(clsName);

if(null==cls){
try {
cls=getIntModelClass(name,fields);
Object wlo = cls.newInstance();
// asm.WorkLoadObject wo=new asm.WorkLoadObject();
cls = wlo.getClass();
// cls.getMethods()[0].invoke(null, new Object[]{null});
java.lang.reflect.Method setMethod = cls.getMethod("setDept1S",
new Class[]{int.class});
setMethod.invoke(wlo, new Object[]{new Integer(10)});
java.lang.reflect.Method getMethod = cls.getMethod("getDept1S",
new Class[]{});
System.out.println(getMethod.invoke(wlo, new Object[]{}));
setMethod = cls.getMethod("setCode", new Class[]{String.class});
setMethod.invoke(wlo, new Object[]{new String("z11")});
getMethod = cls.getMethod("getCode", new Class[]{});
System.out.println(getMethod.invoke(wlo, new Object[]{}));
System.out.println(Type.INT_TYPE.getDescriptor());
} catch (IllegalArgumentException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (SecurityException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (InvocationTargetException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}else{
System.out.println(name+" has been found.");
}

}


public static void main(final String args[]) throws Exception {
DynaModelClassLoader hd = new DynaModelClassLoader();
String className = "asm/setget/WorkLoadObject";
hd.testClass(className,new String []{"dept1S"});
}