When I was working on Spring related projects, I was stuck with this bug for a long time. I found a lot of other people’s blogs on the Internet, and several browsers were opened... I was looking for help from the team leader when I was unable to find it. Assigned a null initial value such as:

List<TermAllRes> termAllResList = null;

Should be changed to:

List<TermAllRes> termAllResList = new ArrayList<TermAllRes>();

Of course, everyone’s bugs are different. Below I will give some examples of common solutions. There should be a solution:

1. The reason for the error is generally that when the service is introduced into the controller, you forgot to write the annotation @Resource or @ Autowired.
2. Introduce spring-boot-starter-actuator in POM:

 <dependency>
     <groupId>org.springframework.boot</groupId>
     <artifactId>spring-boot-starter-actuator</artifactId>
 </dependency>

Note: This package is used for health monitoring.
ps: In fact, the official documentation is also pitted. It may have been developed from the beginning to the present. Some omissions in the documentation have caused some packages to be introduced and not cleared, and even the official sample code is not explained. The above problem appears

3. Possible reason: compilation error
   Solution:
   mvn clean
   mvn package

4. Wrong words for page related attributes

5. Temporarily turn off the search engine server ElasticSearch

6. The service layer implementation class does not add the annotation @Autowired.
   The function of @Autowired is to automatically inject dependent beans.
   Modification method:
   add comment

7. Delete all the antlr folders in the path .m2\repository\

   Then re-use Maven update project

8. Serialization exception
   Solution: serialize pojo
   

9. The exception is caused by the conflict between response.getOutputStream() and response.getWriter(), or the last used information has not been cleared, so the cache needs to be reset.
   Solution: add response.resetBuffer(); before use

   Critical: Servlet.service() for servlet dispatcherServlet threw exception
   java.lang.IllegalStateException: getOutputStream() has already been called for this response
   at org.apache.catalina.connector.Response.getWriter(Response.java:610)
   at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:198)

10. In a Controller, new but not a Controller is ok; then call a service and an error is reported

    Finally, change the new object to injection

ps: When working on a project, we will always encounter bugs. We should face it calmly. Every time we solve a bug, we have a sense of accomplishment! This is the precipitation of knowledge!

Learning is like rowing upstream