Java ASM动态子类创建-NoClassDefFoundError BeanInfo
我正在尝试使用ASM框架动态创建一个子类。 我能够创建类并实例化它。但是当我试着去做的时候Java ASM动态子类创建-NoClassDefFoundError BeanInfo,java,class,dynamic,java-bytecode-asm,beaninfo,Java,Class,Dynamic,Java Bytecode Asm,Beaninfo,我正在尝试使用ASM框架动态创建一个子类。 我能够创建类并实例化它。但是当我试着去做的时候 org.apache.commons.beanutils.BeanUtils.copyProperties(processedEntity, entity); 它抛出以下异常: java.lang.NoClassDefFoundError: com/wheelsup/app/benefits/service/XpOWErhNBiBeanInfo (wrong name: com/wheelsup/ap
org.apache.commons.beanutils.BeanUtils.copyProperties(processedEntity, entity);
它抛出以下异常:
java.lang.NoClassDefFoundError: com/wheelsup/app/benefits/service/XpOWErhNBiBeanInfo (wrong name: com/wheelsup/app/benefits/service/XpOWErhNBi)
下面是我用来创建子类的代码:
Class<? extends T> get() throws Exception {
String superClassInternalName = getInternalName(superClass);
String subClassSimpleName = RandomStringUtils.random(10, true, false);
String subClassInternalName = getClass().getPackage().getName().replaceAll("\\.", "/").concat("/").concat(subClassSimpleName);
String subClassName = getClass().getPackage().getName().concat(".").concat(subClassSimpleName);
ClassWriter classWriter = new ClassWriter(ClassWriter.COMPUTE_FRAMES);
classWriter.visit(Opcodes.V1_6,
ACC_PUBLIC,
subClassInternalName,
null,
superClassInternalName,
null);
visitDefaultConstructor(classWriter, superClassInternalName);
classWriter.visitEnd();
return SubClassLoader.<T>init().load(classWriter.toByteArray(), subClassName);
}
private void visitDefaultConstructor(ClassWriter classWriter, String superClassInternalName) {
MethodVisitor methodVisitor = classWriter.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);
methodVisitor.visitCode();
methodVisitor.visitVarInsn(ALOAD, 0);
methodVisitor.visitMethodInsn(INVOKESPECIAL, superClassInternalName, "<init>", "()V");
methodVisitor.visitInsn(RETURN);
methodVisitor.visitMaxs(0, 0);
methodVisitor.visitEnd();
}
private static class SubClassLoader<T> {
private final ClassLoader contextClassLoader;
private SubClassLoader(ClassLoader contextClassLoader) {
this.contextClassLoader = contextClassLoader;
}
static <U> SubClassLoader<U> init() {
return new SubClassLoader<>(Thread.currentThread().getContextClassLoader());
}
@SuppressWarnings("unchecked")
Class<? extends T> load(byte[] classBytes, String className) throws Exception {
return (Class<? extends T>) new SubClassLoader.DynamicClassLoader(contextClassLoader, classBytes).loadClass(className);
}
private static class DynamicClassLoader extends ClassLoader {
private byte[] rawClassBytes;
private DynamicClassLoader(ClassLoader contextClassLoader, byte[] classBytes) {
super(contextClassLoader);
this.rawClassBytes = classBytes;
}
@Override
public Class findClass(String name) {
return defineClass(name, this.rawClassBytes, 0, this.rawClassBytes.length);
}
}
}
Class所以问题出在类加载器中
private static class SubClassLoader<T> {
private final ClassLoader contextClassLoader;
private SubClassLoader(ClassLoader contextClassLoader) {
this.contextClassLoader = contextClassLoader;
}
static <U> SubClassLoader<U> init() {
return new SubClassLoader<>(Thread.currentThread().getContextClassLoader());
}
@SuppressWarnings("unchecked")
Class<? extends T> load(byte[] classBytes, String className) throws Exception {
return (Class<? extends T>) new DynamicClassLoader(contextClassLoader, classBytes, className).loadClass(className);
}
private static class DynamicClassLoader extends ClassLoader {
private byte[] classBytes;
private final String className;
private DynamicClassLoader(ClassLoader contextClassLoader, byte[] classBytes, String className) {
super(contextClassLoader);
this.classBytes = classBytes;
this.className = className;
}
@Override
public Class findClass(String className) throws ClassNotFoundException {
if (StringUtils.equals(this.className, className)) {
return defineClass(className, this.classBytes, 0, this.classBytes.length);
}
throw new ClassNotFoundException(className);
}
}
}
私有静态类子类加载器{
私有最终类加载器contextClassLoader;
私有子类加载器(类加载器上下文类加载器){
this.contextClassLoader=contextClassLoader;
}
静态子类装入器init(){
返回新的子类加载器(Thread.currentThread().getContextClassLoader());
}
@抑制警告(“未选中”)
类问题在于findClass
实现尝试返回生成的类,而不管调用方请求哪个类。在某些情况下,无法加载类是使操作正常工作的正确方法
BeanUtils
类依赖于,它允许为检查的类执行可选的显式beaninfo实现,因此,如果被要求提供Foo
的beaninfo
,它将首先尝试加载一个类FooBeanInfo
,如果失败,它将为Foo
构造一个通用的beaninfo
但是,由于您的findClass
实现试图(重新)以错误的名称xpowerhnbieaninfo
构建xpowerhnbieaninfo
类,而不是报告缺少xpowerhnbieaninfo
,因此出现了问题
您必须更改子类加载器
以接收所生成类的预期名称。然后,您可以将findClass
实现更改为
@Override
public Class findClass(String name) throws ClassNotFoundException {
if(!name.equals(expectedName))
throw new ClassNotFoundException(name);
return defineClass(name, this.rawClassBytes, 0, this.rawClassBytes.length);
}
一个更简单但有黑客攻击性的解决方案是,在第一个类构造之后,null
取出rawClassBytes
,并为每个后续类加载请求抛出一个ClassNotFoundException
,作为继承的标准loadClass
实现保证调用findClass
只加载类,因此只要立即加载生成类的程序逻辑没有改变,所有后续请求都是关于不同的、不受支持的类
但是,由于关键点是程序逻辑不能更改,我不建议使用这种黑客、脆弱的解决方案。将生成的类的名称传递给自定义加载程序并进行验证,一开始代码要多一些,但要干净得多。谢谢Holger!我在研究了类加载程序impl(即我们的类加载程序)后找到了解决方案在ByteBuddy框架中进行编辑,这正是您所说的。