How to specify the execution order for multiple global exception handling classes

background

In the project , We usually define a global exception handling class to handle exceptions uniformly , While standardizing the code, it also improves the development efficiency , With the global exception handling class , Except in special circumstances , Most of the time , We just need to throw the anomaly out , Subsequently, the exception handling class will uniformly log , Encapsulate the exception information into the unified response object and then return .

But sometimes , Large projects , Will encapsulate different basic project dependencies , Put some commonly used , Common functions are encapsulated into different projects , Then the rest of the projects introduce dependencies , To use these features , This can ensure the uniformity and standardization of relevant projects , And it is easier to expand these general functions in the future , In fact, it is also an abstract thought , If there is a global exception handling class in the basic dependency , The project introduces this basic dependency , This global exception handling class will be injected at startup , But this global exception handling class is not a special case exception handling that can meet individual projects , For example, it's not right sql abnormal , Special treatment shall be carried out for parameter verification exceptions , It will cause these exceptions to be finally caught and handled by the bottom exception , The output response result may not be what we want , At that time , We need to define the global exception handling classes required by our project .

Why should we specify the order of execution

Suppose we also define a global exception handling class in the project , When the project starts , Two global exception handling classes will be injected , and spring The logic for handling exceptions is straightforward , It is to traverse the global exception handler list in order , If the exception handler can handle the exception , Subsequent exception handlers will no longer handle this exception , So if the basic exception handler is at the top of the list , The special exception handler we defined is behind the basic exception handler , Then the specific exception we throw , It will still not be processed by a specific processor , The response result obtained is also the response information encapsulated by the basic exception handler . Therefore, it is important to specify the execution order of global exception handling classes .

How to specify the execution sequence ？

adopt @Order() annotation , The annotation is on the global exception handling class , The smaller the order , Earlier injection , We just need to guarantee @Order() The value of is smaller than the basic global exception handling class , You can control the order of the global exception handler list .

Provide a way to check and confirm

If used @Order() Annotations have not yet implemented the requirements , Then enter first DispatcherServlet.class -> Enter the processDispatchResult() Method -> Enter processHandlerException() Method , you 're right , This processHandlerException() Method is the method of handling exceptions .

Interception part processHandlerException() The code in the method , We can break here ：

By looking at HandlerExceptionResolver Class exceptionHandlerAdviceCache attribute , We can view the global exception handler list , The general structure of this attribute is as follows ：

private final Map<ControllerAdviceBean, ExceptionHandlerMethodResolver> exceptionHandlerAdviceCache = new LinkedHashMap();

You can find that the global exception handler list is through LinkedHashMap For maintenance. , So we can see the global exception handler in LinkedHashMap The sorting , We can know whether the global exception handler we define is successfully sorted in front of the basic global exception handler .