Json在Jersey REST应用程序中响应严重错误

Question

I'm learning JERSEY REST API with maven. I'm getting following error whey i hit GET request. Interesting point is when i return only specific class object, i'm getting the desired result but when i return a map of all those objects i'm getting this error with Status 500 - Internal Server Error. Please suggest.

Error:

SEVERE: MessageBodyWriter not found for media type=application/json, 
type=class java.util.HashMap, genericType=java.util.Map<java.lang.Integer, message.Message>.

Error prone:

@GET
@Produces(MediaType.APPLICATION_JSON)
public Map<Integer,Message> getAll(){
    ms.sample();
    return ms.getAllMessages();

}

Same code but returning specific object, works fine:

@GET
@Produces(MediaType.APPLICATION_JSON)
public Message getAll(){
    ms.sample();
    return ms.getAllMessages().get(1);

}

PS : I've added json related element in pom.xml file as follows

    <dependency>
        <groupId>org.glassfish.jersey.media</groupId>
        <artifactId>jersey-media-moxy</artifactId>
    </dependency>

I'm using Maven v2.16

Answer 1

Add following dependency

<dependency>
  <groupId>org.glassfish.jersey.media</groupId>
  <artifactId>jersey-media-json-jackson</artifactId>

</dependency>

Answer 2

MOXy and Map s are not friends... I recommend you using Jackson instead of MOXy to (de)serialize JSON.

To do it, remove the jersey-media-moxy dependency and add the following:

<dependency>
    <groupId>org.glassfish.jersey.media</groupId>
    <artifactId>jersey-media-json-jackson</artifactId>
    <version>2.23.1</version>
</dependency>

For more details, check Jersey documentation .