Jersey Exception : SEVERE: A message body reader for Java class

Question

I have a Jersey based Rest WS which outputs JSON. I am implementing a Jersey Client to invoke the WS and consume the JSON response. The client code I have is below

Answer 1

I was able to fix the issue by adding the maven dependency for jersey-json.

Answer 2

In my case, I'm using POJO. And I forgot configure POJOMappingFeature as true. Maycon has pointed it out in an early answer. However some guys might have trouble to configure it in web.xml correctly, here is my example.

<servlet>
    <servlet-name>Jersey Servlet</servlet-name>
    <servlet-class>com.sun.jersey.spi.spring.container.servlet.SpringServlet</servlet-class>
    <init-param>
        <param-name>com.sun.jersey.api.json.POJOMappingFeature</param-name>
        <param-value>true</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>

Answer 3

Mine was similar situation. I get this error in crucial times and I did not remember how I had solved it before, which I did many number of times. After strenuous hours of inspection, I have solved and reproduced the error and made sure how simple is the solution for this situation.

Okay - solution : remove (or correct) any newly made changes to your main project's properties files.

Yes, this is it. In fact, my project is a multi-moduled huge one, and you know going without correct dependencies is a rare case scenario as is fetched often from git (RAC too). My project was getting almost all configurable things from a properties file that is common to about 15 or so modules (sub projects) with good amount of intra-dependencies among them. jersey-json's dependency is always there in my merged parent pom. XML Annotations aren't a problem as the project is being run for around 100 times after modifying them. some solutions here point to web.xml and things like POJOMappingFeature. In my case, I haven't even touched the webapp module in this build. so anyhow, this solution worked for me and I am spending time to record this in SO in case if I ever happen to fall into this error, I would not have to waste my sleepy nights. (of course, for you too)

Answer 4

for Python and Swagger example:

import requests
base_url = 'https://petstore.swagger.io/v2'
def store_order(uid):
    api_url = f"{base_url}/store/order"
    api_data = {
        'id':uid,
        "petId": 0,
        "quantity": 0,
        "shipDate": "2020-04-08T07:56:05.832Z",
        "status": "placed",
        "complete": "true"
        }
    # is a kind of magic..
    r = requests.post(api_url, json=api_data)
    return r
print(store_order(0).content)    

Most important string with MIME type: r = requests.post(api_url, json=api_data)

Answer 5

Just add below lines in your POJO before start of class ,and your issue is resolved. @Produces("application/json") @XmlRootElement See example import javax.ws.rs.Produces; import javax.xml.bind.annotation.XmlRootElement;

 /**
 * @author manoj.kumar
 * @email kumarmanoj.mtech@gmail.com
 */
 @Produces("application/json")
 @XmlRootElement  
 public class User {

 private String username;
 private String password;
 private String email;
 public String getUsername() {
 return username;
 }
 public void setUsername(String username) {
     this.username = username;
 }
 public String getPassword() {
     return password;
 }
 public void setPassword(String password) {
     this.password = password;
 }
 public String getEmail() {
    return email;
 }
 public void setEmail(String email) {
    this.email = email;
 }

}
add below lines inside of your web.xml
<init-param>
    <param-name>com.sun.jersey.api.json.POJOMappingFeature</param-name>
    <param-value>true</param-value>
</init-param>  
Now recompile your webservice everything would work!!!

Answer 6

We also decided to use jersey as a solution. But as we are using org.JSON in most of the cases this dependency is unecessary and we felt not good.

Therefore we used the String representation to get a org.JSON object, instead of

JSONObject output = response.getEntity(JSONObject.class); 

we use it this way now:

JSONObject output = new JSONObject(response.getEntity(String.class)); 

where JSONObject comes from org.JSON and the imports could be changed from:

-import org.codehaus.jettison.json.JSONArray;
-import org.codehaus.jettison.json.JSONException;
-import org.codehaus.jettison.json.JSONObject;
+import org.json.JSONArray;
+import org.json.JSONException;
+import org.json.JSONObject;