Spring RestController - No converter found for return value of type java.lang.Integer

Question

I am currently trying to create my first rest service with spring , I wan't him to return XML result (based on JAXB) .

on a very basic rest controller:

import org.springframework.web.bind.annotation.*;
import java.util.ArrayList;
import java.util.List;

@RestController
public class CVIController {
    @RequestMapping(value = "/resume")
    public @ResponseBody
    Integer getResume() {
        return 5;
    }
}

with a spring-servlet.xml pretty empty:

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd
http://www.springframework.org/schema/mvc
http://www.springframework.org/schema/mvc/spring-mvc.xsd">
    <context:component-scan base-package="fr.urouen"
    />
    <mvc:annotation-driven />
</beans>

And a Tomcat server under JDK8 so I can be sure that all modules are load by default on the JVM... I got the following exception throwed:

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.IllegalArgumentException: No converter found for return value of type: class java.lang.Integer

I don't wan't to use Jackson because I know that JAXB can handle this. But after juggle with some part of my code, I still can't found the answer of why she is throwed.

Edit 1:

I tried to create a dummy class with getters as answers said

public class Dummy {
    private int value;


    public int getValue() {
        return value;
    }

    public void setValue(int value) {
        this.value = value;
    }
}

@RestController
public class CVIController {
    @RequestMapping(value = "/resume")
    public ResponseEntity<Dummy> getResume() {
        Dummy dummy = new Dummy();
        dummy.setValue(5);
        return new ResponseEntity<Dummy>(dummy, HttpStatus.OK);
    }
}

But still got the exact same result :

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.IllegalArgumentException: No converter found for return value of type: class fr.urouen.model.Dummy

Answer 1

The simplest solution is to return a String and remove the @ResponseBody annotation. As a rest controller, by definition, returns a string, that's the way to go for this specific example.

If you are after a more comprehensive solution, Spring by default uses Jackson to do the conversion from object to JSON. The @ResponseBody does that automatically.

Im pretty sure that Integer won't work because it's not a POJO with getters and setters and something that can be converted to JSON. ie { 5 } is not a valid JSON object.

if you had a class like this:

public class returnObject() {
  private int value;
  ... getters/setters
}

and then did this:

@RestController
@ResponseBody
public ReturnObject getValue() {
   ReturnObject ret = new ReturnObject();
   ret.setValue(5);
   return ret;
}

You would then get this:

{ "value" : 5 }

You will also need to add jackson to your pom:

<dependency>
  <groupId>com.fasterxml.jackson.core</groupId>
  <artifactId>jackson-databind</artifactId>
  <version>2.9.4</version>
</dependency>

Answer 2

ResponseEntity is used for a return some content from restcontroller, Have you tried with ResponseEntity ?

@RestController
public class CVIController {
    @RequestMapping(value = "/resume")
    public @ResponseBody ResponseEntity<?> getResume() {
        return ResponseEntity.ok(5);
    }
}

or you can write

@RestController
public class CVIController {
    @RequestMapping(value = "/resume")
    public @ResponseBody ResponseEntity<Integer> getResume() {
        return new ResponseEntity<Integer>(5, HttpStatus.OK);
    }
}

more example you can get from here

Answer 3

我也遇到了这个问题，尝试下载jackson-databind.jar、ackson-core.jar、ackson-annotations.jar，放到你的WEB-INF/lib目录下