No default constructor found; nested exception is

问题:

I am working with Spring MVC controller project. Below is my Controller and I have a constructor declared which I am specifically using for testing purpose.

@Controller
public class TestController {

    private static KeeperClient testClient = null;

    static {

    // some code here

    }

    /**
     * Added specifically for unit testing purpose.
     * 
     * @param testClient
     */
    public TestController(KeeperClient testClient) {
        TestController.testClient = testClient;
    }

    // some method here

}

Whenever I am starting the server, I am getting below exception -

No default constructor found; nested exception is java.lang.NoSuchMethodException:

But if I remove TestController constructor then it works fine without any problem. What wrong I am doing here?

But if I add this default constructor then it starts working fine -

    public TestController() {

    }

回答1:

You must have to define no-args or default constructor if you are creating your own constructor.

You can read why default or no argument constructor is required.

why-default-or-no-argument-constructor-java-class.html

回答2:

Spring cannot instantiate your TestController because its only constructor requires a parameter. You can add a no-arg constructor or you add @Autowired annotation to the constructor:

@Autowired
public TestController(KeeperClient testClient) {
    TestController.testClient = testClient;
}

In this case, you are explicitly telling Spring to search the application context for a KeeperClient bean and inject it when instantiating the TestControlller.

回答3:

In my case, spring threw this because i forgot to make an inner class static.

When you found that it doesnt help even adding a no-arg constructor, please check your modifier.

回答4:

In my case I forgot to add @RequestBody annotation to the method argument:

public TestController(@RequestBody KeeperClient testClient) {
        TestController.testClient = testClient;
    }