Unified exception handling causes ResponseBodyAdvice to fail

Background

Under the microservice architecture, some basic functions are planned to be extracted into the public Jar package, including unified exception handling, JwtToken verification, unified request response processing, etc. After the extraction, it is found that when an exception occurs, the unified exception capture method is used.Logic, but all the custom ResponseBodyAdvice in the project are not executed, decided to debug step by step to locate the reason, the project is Springboot 2.3.7.RELEASE version.

Location Process

First, test the normal interface and find that the ResponseBodyAdvices are all valid and executed in the order of settings, indicating that these ResponseBodyAdvices are all registered to the container.

Then guess whether ResponseBodyAdvice has been executed but the beforeBodyWrite method has not been executed, and it has returned when the supports method is executed, so a breakpoint is placed in the supports method to see if it will go to the supports method when an exception is thrown, and finally found that allWithout taking the supports method, I guess it may be because of some rules that the ResponseBodyAdvice is filtered.

Continue to DEBUG to see how ResponseBodyAdvice takes effect in the normal process, because a breakpoint has been set in the supports method before, and the interface is directly requested to see the call stack before the supports method, as shown in the figure

Mainly the first few classes, the top of the stack is my custom ResponseBodyAdvice, the breakpoint is on the supports method, the following is line 140 of the processBody method of RequestResponseBodyAdviceChain, then line 116 of the beforeBodyWrite method of RequestResponseBodyAdviceChain, and line 268 of writeWithMessageConverters of the AbstractMessageConverterMethodProcessor class, break points on these methods respectively:

The following will take the beforeBodyWrite method of RequestResponseBodyAdviceChain, continue to go in and see

The inside of the for loop is to actually call each advice to process the returned results. To filter, it can only be done in the getMatchingAdvice method, and continue DEBUG

getAdvice() is to get all the Advice in the system. Because the custom ResponseBodyAdvice is decorated with @ControllerAdvice annotation, it is all ControllerAdviceBean type, and it takes 157 lines of logic.The parameter parameter is the method parameter that finally returns the data. Here I am the method of unified exception handling.Continue to enter

You can see that this method calls the test method of beanTypePredicate. There are three properties in beanTypePredicate, one of which is basePackages. In the custom ResponseBodyAdvice @RestControllerAdvice specifies the package name, and the other two assignableTypes and annotations are also the annotationsAttributes.Continue to see the content of the test method

At this point, you can probably know the reason, that is, the package name does not match, and ResponseBodyAdvice can only process the return value under the specified package name.The other two properties can implement the function of the specified annotation or the Class class to implement the ResponseBodyAdvice:

• annotations attribute, if the returned method is not in the basePackages package, specify this annotation directly on the method
• assignableTypes attribute, if it is not in the basePackages package and there is no annotations annotation, you can also specify the Class class

reason

The package name of the unified exception handling class is not under the package name specified by the basePackages attribute of the @RestControllerAdvice annotation, so the custom ResponseBodyAdvice cannot process the data returned by the unified exception handling

Workaround

• Modify the package name, the package name of basePackages contains the class for unified exception handling
• Add a custom annotation, decorate it on the exception handling method, and write this annotation on the annotations attribute of the @RestControllerAdvice annotation
• Write the class object of exception handling on the assignableTypes attribute of the @RestControllerAdvice annotation

Summary

See the source code for frame exceptions, debug more, and gain a lot.