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如果Controller里有私有的方法,能成功访问吗?
🐳 我就是我🐳
2022-11-23 21:15:45 2022-11-23
16
0

目录

背景

写代码的时候,复制粘贴的时候,没注意到方法的属性,就导致了Controller里有了一个私有的方法,然后访问这个接口的时候就报了空指针异常,找了好久才找到是这个原因。

来看一个例子

@Service
public class MyService {
public String hello() {
return "hello";
}
}
@Slf4j
@RestController
@RequestMapping("/test")
public class MyController {
@Autowired
private MyService myService;
@GetMapping("/public")
public Object publicHello() {
return myService.hello();
}
@GetMapping("/protected")
protected Object protectedHello() {
return myService.hello();
}
@GetMapping("/private")
private Object privateHello() {
return myService.hello();
}
}
@EnableAspectJAutoProxy
@SpringBootApplication(exclude = {DataSourceAutoConfiguration.class})
public class MyApplication {
public static void main(String[] args) {
SpringApplication.run(MyApplication.class, args);
}
}
访问 
http://127.0.0.1:8081/test/public 200
http://127.0.0.1:8081/test/protected 200
http://127.0.0.1:8081/test/private 200

如果在这个基础之上再加一个切面:

@Slf4j
@Aspect
@Component
public class MyAspect {
@Pointcut("execution(* cn.eagle.li.controller..*.*(..))")
public void controllerSayings() {
}
@Before("controllerSayings()")
public void sayHello() {
log.info("注解类型前置通知");
}
}
访问 
http://127.0.0.1:8081/test/public 200
http://127.0.0.1:8081/test/protected 200
http://127.0.0.1:8081/test/private 500:报空指针异常,原因是myService为null的

原因

  • public 方法
  • protected 方法
  • private 方法

大致可以看到原因,public方法和protected方法访问的时候,它的类都是真实的类

而private方法是代理的类

cglib代理的锅

Spring Boot 2.0 开始,默认使用的是cglib代理

@Configuration
@ConditionalOnClass({ EnableAspectJAutoProxy.class, Aspect.class, Advice.class,
AnnotatedElement.class })
@ConditionalOnProperty(prefix = "spring.aop", name = "auto", havingValue = "true",
matchIfMissing = true)
public class AopAutoConfiguration {
@Configuration
@EnableAspectJAutoProxy(proxyTargetClass = false)
@ConditionalOnProperty(prefix = "spring.aop", name = "proxy-target-class",
havingValue = "false", matchIfMissing = false)
public static class JdkDynamicAutoProxyConfiguration {
}
@Configuration
@EnableAspectJAutoProxy(proxyTargetClass = true)
@ConditionalOnProperty(prefix = "spring.aop", name = "proxy-target-class",
havingValue = "true", matchIfMissing = true)
public static class CglibAutoProxyConfiguration {
}
}

入口

不管public还是private的方法,都是这样执行的。

生成代理类字节码

public static void main(String[] args) {
/** 加上这句代码,可以生成代理类的class文件*/
System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "org/springframework/cglib");
SpringApplication.run(MyApplication.class, args);
}

部分代理类字节码如下:

protected final Object protectedHello() {
try {
MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
if (var10000 == null) {
CGLIB$BIND_CALLBACKS(this);
var10000 = this.CGLIB$CALLBACK_0;
}
return var10000 != null ? var10000.intercept(this, CGLIB$protectedHello$1$Method, CGLIB$emptyArgs, CGLIB$protectedHello$1$Proxy) : super.protectedHello();
} catch (Error | RuntimeException var1) {
throw var1;
} catch (Throwable var2) {
throw new UndeclaredThrowableException(var2);
}
}
public final Object publicHello() {
try {
MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
if (var10000 == null) {
CGLIB$BIND_CALLBACKS(this);
var10000 = this.CGLIB$CALLBACK_0;
}
return var10000 != null ? var10000.intercept(this, CGLIB$publicHello$0$Method, CGLIB$emptyArgs, CGLIB$publicHello$0$Proxy) : super.publicHello();
} catch (Error | RuntimeException var1) {
throw var1;
} catch (Throwable var2) {
throw new UndeclaredThrowableException(var2);
}
}

public和protected方法会生成上述的方法,而private方法是不会生成这样的方法

private static class DynamicAdvisedInterceptor implements MethodInterceptor, Serializable {
@Override
@Nullable
public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
Object oldProxy = null;
boolean setProxyContext = false;
Object target = null;
TargetSource targetSource = this.advised.getTargetSource();
try {
if (this.advised.exposeProxy) {
// Make invocation available if necessary.
oldProxy = AopContext.setCurrentProxy(proxy);
setProxyContext = true;
}
// Get as late as possible to minimize the time we "own" the target, in case it comes from a pool...
target = targetSource.getTarget();
Class<?> targetClass = (target != null ? target.getClass() : null);
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
Object retVal;
// Check whether we only have one InvokerInterceptor: that is,
// no real advice, but just reflective invocation of the target.
if (chain.isEmpty() && Modifier.isPublic(method.getModifiers())) {
// We can skip creating a MethodInvocation: just invoke the target directly.
// Note that the final invoker must be an InvokerInterceptor, so we know
// it does nothing but a reflective operation on the target, and no hot
// swapping or fancy proxying.
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
retVal = methodProxy.invoke(target, argsToUse);
}
else {
// We need to create a method invocation...
retVal = new CglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy).proceed();
}
retVal = processReturnType(proxy, target, method, retVal);
return retVal;
}
finally {
if (target != null && !targetSource.isStatic()) {
targetSource.releaseTarget(target);
}
if (setProxyContext) {
// Restore old proxy.
AopContext.setCurrentProxy(oldProxy);
}
}
}
}

public和protected方法会调用DynamicAdvisedInterceptor.intercept方法,这里面的this.advised.getTargetSource()可以获得真实的目标类,这个目标类是注入成功。

换成JDK动态代理呢

增加配置:

spring:
aop:
proxy-target-class: false

增加接口:

@RestController
public interface MyControllerInterface {
@RequestMapping("/hello/public")
Object publicHello();
@RequestMapping("/hello/default")
default Object defaultHello() {
return "hi default";
}
}
@Slf4j
@RestController
@RequestMapping("/test")
public class MyController implements MyControllerInterface {
@Autowired
public MyService myService;
@Override
@GetMapping("/public")
public Object publicHello() {
return myService.hello();
}
@GetMapping("/protected")
protected Object protectedHello() {
return myService.hello();
}
@GetMapping("/private")
private Object privateHello() {
return myService.hello();
}
}

MyControllerInterface头上加@RestController的原因是:

protected boolean isHandler(Class<?> beanType) {
return (AnnotatedElementUtils.hasAnnotation(beanType, Controller.class) ||
AnnotatedElementUtils.hasAnnotation(beanType, RequestMapping.class));
}
http://127.0.0.1:8081/test/public 404
http://127.0.0.1:8081/test/protected 404
http://127.0.0.1:8081/test/private 404
http://127.0.0.1:8081/hello/public 200
http://127.0.0.1:8081/hello/default 200

只能使用接口里的@RequestMapping,实现类里的不生效

参考

听说SpringAOP 有坑?那就来踩一踩

源码角度深入理解JDK代理与CGLIB代理

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