HTTP Status 500, Jersey Rest how to solve?

Question

Java

localhost:8080/main/say gives 500 error.
Details:

package com.mkyong.rest;
 
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.PathParam;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;


@Path("/main")
public class HelloWorldService {
 
  @GET
  @Path("/{param}")
  public Response getMsg(@PathParam("param") String msg) {

    String output = "Jersey say : " + msg;
 
    return Response.status(200).entity(output).build();
 
  }

  @GET
  @Produces(MediaType.APPLICATION_JSON)
  @Path("say")
  public User getUser() {


    User u1 = new User();
    u1.setName("Alex");
    u1.setOld(23);
    
    return u1;
  } 
}

package com.mkyong.rest;

public class User {
    
    private String name;

    private int old;

    public String getName() {
        return name;
    }

    public int getOld() {
        return old;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setOld(int old) {
        this.old = old;
    }
}

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.mkyong.common</groupId>
  <artifactId>RESTfulExample</artifactId>
  <packaging>war</packaging>
  <version>1.0-SNAPSHOT</version>
  <name>RESTfulExample Maven Webapp</name>
  <url>http://maven.apache.org</url>

  <repositories>
    <repository>
      <id>maven2-repository.java.net</id>
      <name>Java.net Repository for Maven</name>
      <url>http://download.java.net/maven/2/</url>
      <layout>default</layout>
    </repository>
  </repositories>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.8.2</version>
      <scope>test</scope>
    </dependency>

    <dependency>
      <groupId>com.sun.jersey</groupId>
      <artifactId>jersey-server</artifactId>
      <version>1.8</version>
    </dependency>



  </dependencies>

  <build>
    <finalName>RESTfulExample</finalName>
    <plugins>
      <plugin>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
          <source>1.6</source>
          <target>1.6</target>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

<web-app id="WebApp_ID" version="2.4"
  xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee 
  http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
  <display-name>Restful Web Application</display-name>

  <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>com.mkyong.rest</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>

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