Spring Cloud 下使用Javassist 在类被加载之前修改字节码

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.ApplicationContextInitializer;
import org.springframework.context.ConfigurableApplicationContext;

import java.io.IOException;
import java.util.*;

/**
 * @author: 
 * date: 2088/15/19
 */
public abstract class BaseApplicationContextInitializer implements ApplicationContextInitializer {
 protected Logger log = LoggerFactory.getLogger(getClass());

 private static volatile int initialized = 0;

 @Override
 public void initialize(ConfigurableApplicationContext applicationContext) {
 Optional<String> optional = Arrays.stream(applicationContext.getEnvironment().getActiveProfiles())
 .filter(t -> "online".equals(t) || "unittest".equals(t))
 .findFirst();

 if (optional.isPresent()) {
 return;
 }

 if (initialized == 1) {
 log.info(getClass().getSimpleName() + " begin");
 try {
 doJavassist();
 log.info(getClass().getSimpleName() + " end");
 } catch (Throwable e) {
 log.error(getClass().getSimpleName(), e);
 throw new RuntimeException(e);
 }

 initialized += 1;
 }
 if (initialized == 0) {
 initialized += 1;
 }
 }

 protected abstract void doJavassist() throws Exception;


}

import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtMethod;
import javassist.CtNewMethod;

import java.util.Random;

/**
 * @author: 
 * date: 2088/15/19
 */
public class RandomStringUtilsAop extends BaseApplicationContextInitializer {

 @Override
 protected void doJavassist() throws Exception {
 ClassPool classPool = ClassPool.getDefault();

 classPool.importPackage("java.util.Random");

 CtClass randomStringUtilsClass = classPool.get("org.apache.commons.lang3.RandomStringUtils");

 CtClass[] paramsClasses = new CtClass[]{
 classPool.get(int.class.getName()),
 classPool.get(int.class.getName()),
 classPool.get(int.class.getName()),
 classPool.get(boolean.class.getName()),
 classPool.get(boolean.class.getName()),
 classPool.get(char[].class.getName()),
 classPool.get(Random.class.getName())
 };

 CtMethod ctMethod = randomStringUtilsClass.getDeclaredMethod("random", paramsClasses);
 CtMethod srcInvoke = CtNewMethod.copy(ctMethod, randomStringUtilsClass, null);
 srcInvoke.setName("srcInvoke");
 randomStringUtilsClass.addMethod(srcInvoke);

 ctMethod.setBody("{\n" +
 " String className = \"org.apache.commons.lang3.RandomStringUtils\";\n" +
 " String methodName = \"random\";\n" +
 " String result = null;\n" +
 " Throwable ex = null;\n" +
 "\n" +
 " try {\n" +
 " result = srcInvoke($$);\n" +
 " } catch (RuntimeException e) {\n" +
 " ex = e;\n" +
 " }\n" +
 "\n" +
 " RecordUtils.record(className, methodName, result, ex);\n" +
 " if (ex != null) {\n" +
 " throw ex;\n" +
 " }\n" +
 " return result;\n" +
 " }");

 randomStringUtilsClass.toClass();//加载修改后的类，注意：必须保证调用前此类未加载
 if (randomStringUtilsClass.isFrozen()) {
 randomStringUtilsClass.defrost();
 }
 }



}