我看到别人说有三种方法可以动态生成类， 反射时的GeneratedConstructorAccessor和动态代理以及CGLib技术。
请问各位大牛，有谁实现了吗？？最好给出源代码。。。
------解决思路----------------------
在比较高层的上面，可以用一些设计模式
在比较低层的上面，可以用一些反射技术
------解决思路----------------------
可以用javassist
------解决思路----------------------
曾经写过的一个例子：
package com.test.dyna;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.URI;
import java.security.SecureClassLoader;
import java.util.ArrayList;
import java.util.List;
import javax.tools.FileObject;
import javax.tools.ForwardingJavaFileManager;
import javax.tools.JavaCompiler;
import javax.tools.JavaFileManager;
import javax.tools.JavaFileObject;
import javax.tools.SimpleJavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;
import javax.tools.JavaFileObject.Kind;
public class DynaCompTest {
public static void main(String[] args) throws InstantiationException,
IllegalAccessException, ClassNotFoundException {
// TODO Auto-generated method stub
// Full name of the class that will be compiled.
// If class should be in some package,
// fullName should contain it too
// (ex. "testpackage.DynaClass")
String fullName = "com.test.dyna.DynaClass";
// Here we specify the source code of the class to be compiled
StringBuilder src = new StringBuilder();
src.append("package com.test.dyna;\n");
src.append("import com.test.dyna.RecordAccessor;\n");
src.append("public class DynaClass extends RecordAccessor{\n");
src.append(" public String toString() {\n");
src.append(" return \"Hello, I am \" + ");
src.append("this.getClass().getSimpleName();\n");
src.append(" }\n");
src.append(" protected void sayHello() {\n");
src.append(" System.out.println(\"Hello World!!!!\");\n");
src.append(" }\n");
src.append("}\n");
System.out.println(src);
// We get an instance of JavaCompiler. Then
// we create a file manager
// (our custom implementation of it)
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
JavaFileManager fileManager = new ClassFileManager(
compiler.getStandardFileManager(null, null, null));
// Dynamic compiling requires specifying
// a list of "files" to compile. In our case
// this is a list containing one "file" which is in our case
// our own implementation (see details below)
List<JavaFileObject> jfiles = new ArrayList<JavaFileObject>();
jfiles.add(new CharSequenceJavaFileObject(fullName, src));
// We specify a task to the compiler. Compiler should use our file
// manager and our list of "files".
// Then we run the compilation with call()
compiler.getTask(null, fileManager, null, null, null, jfiles).call();
// Creating an instance of our compiled class and
// running its toString() method
Object instance = fileManager.getClassLoader(null).loadClass(fullName)
.newInstance();
System.out.println(instance);
RecordAccessor rd = (RecordAccessor) instance;
rd.sayHello();
}
}
class ClassFileManager extends ForwardingJavaFileManager {
/**
* Instance of JavaClassObject that will store the compiled bytecode of our
* class
*/
private JavaClassObject jclassObject;
/**
* Will initialize the manager with the specified standard java file manager
*
* @param standardManger
*/
public ClassFileManager(StandardJavaFileManager standardManager) {
super(standardManager);
}
/**
* Will be used by us to get the class loader for our compiled class. It
* creates an anonymous class extending the SecureClassLoader which uses the
* byte code created by the compiler and stored in the JavaClassObject, and
* returns the Class for it
*/
@Override
public ClassLoader getClassLoader(Location location) {
return new SecureClassLoader() {
@Override
protected Class<?> findClass(String name)
throws ClassNotFoundException {
byte[] b = jclassObject.getBytes();
return super.defineClass(name, jclassObject.getBytes(), 0,
b.length);
}
};
}
/**
* Gives the compiler an instance of the JavaClassObject so that the
* compiler can write the byte code into it.
*/
@Override
public JavaFileObject getJavaFileForOutput(Location location,
String className, Kind kind, FileObject sibling) throws IOException {
jclassObject = new JavaClassObject(className, kind);
return jclassObject;
}
}
class CharSequenceJavaFileObject extends SimpleJavaFileObject {
/**
* CharSequence representing the source code to be compiled
*/
private CharSequence content;
/**
* This constructor will store the source code in the internal "content"
* variable and register it as a source code, using a URI containing the
* class full name
*
* @param className
* name of the public class in the source code
* @param content
* source code to compile
*/
public CharSequenceJavaFileObject(String className, CharSequence content) {
super(URI.create("string:///" + className.replace('.', '/')
+ Kind.SOURCE.extension), Kind.SOURCE);
this.content = content;
}
/**
* Answers the CharSequence to be compiled. It will give the source code
* stored in variable "content"
*/
@Override
public CharSequence getCharContent(boolean ignoreEncodingErrors) {
return content;
}
}
class JavaClassObject extends SimpleJavaFileObject {
/**
* Byte code created by the compiler will be stored in this
* ByteArrayOutputStream so that we can later get the byte array out of it
* and put it in the memory as an instance of our class.
*/
protected final ByteArrayOutputStream bos = new ByteArrayOutputStream();
/**
* Registers the compiled class object under URI containing the class full
* name
*
* @param name
* Full name of the compiled class
* @param kind
* Kind of the data. It will be CLASS in our case
*/
public JavaClassObject(String name, Kind kind) {
super(
URI.create("string:///" + name.replace('.', '/')
+ kind.extension), kind);
}
/**
* Will be used by our file manager to get the byte code that can be put
* into memory to instantiate our class
*
* @return compiled byte code
*/
public byte[] getBytes() {
return bos.toByteArray();
}
/**
* Will provide the compiler with an output stream that leads to our byte
* array. This way the compiler will write everything into the byte array
* that we will instantiate later
*/
@Override
public OutputStream openOutputStream() throws IOException {
return bos;
}
}