找不到Java类java.util.ArrayList和Java类型类java.util.ArrayList和MIME媒体类型application / json的消息正文编写器

Question

I am new to using jersy for implementing rest api

I get the below error, when I call the products service.

 com.sun.jersey.api.MessageException: A message body writer for Java class java.util.ArrayList, and Java type class java.util.ArrayList, and MIME media type application/json was not found.

Here is my code:

@GET
@Path("/products")
@Produces(MediaType.APPLICATION_JSON)
public Response productSearch(@QueryParam("name") String name)
{
   List<Product> products = new ArrayList<>();
   products.add(new Product("PRDNAME", "PRDCOST", "PRDMODEL"));
   return Response.ok( products).build();
}

I also tried this:

@GET
@Path("/products")
@Produces(MediaType.APPLICATION_JSON)
public List<Product> productSearch(@QueryParam("name") String name)
{
   List<Product> products = new ArrayList<>();
   products.add(new Product("PRDNAME", "PRDCOST", "PRDMODEL"));
   return products;
}

The below is the setup of my environment:

• Tomcat 8,
• Jersey libraries: jersey-bundle-1.19.1,
• Not using maven

web.xml:

    <servlet>
        <servlet-name>jersey-serlvet</servlet-name>
        <servlet-class>com.sun.jersey.spi.container.servlet.ServletContainer</servlet-class>
        <init-param>
            <param-name>com.sun.jersey.config.property.packages</param-name>
            <param-value>org.test.rest</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>jersey-serlvet</servlet-name>
        <url-pattern>/rest/*</url-pattern>
    </servlet-mapping>

I tried using the below init-param also:

    <init-param>  
      <param-name>com.sun.jersey.api.json.POJOMappingFeature</param-name>  
      <param-value>true</param-value>  
    </init-param>

I tried returning GenericEntity, but had the same issue.

return Response.ok().entity(new GenericEntity<List<Product>>(products) {}).build();

I also tried using

• jersey-core-1.8.jar
• jersey-json-1.8.jar
• jersey-server-1.8.jar

instead of jersey-bundle-1.19.1

I don't have any issues when I return string. I understand, I am missing the json media type dependency, but could not figure it out.

This error happens on the tomcat server while the client doesn't receive response obviously.

Answer 1

Maybe you forgot to add

@XmlRootElement

annotation on top of model class definition. For your "Product" model, I guess it would be something like

import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class Product{
....
}

I had a similar exception and this solved it for me.