不包含任何根资源类ResourceConfig实例

Question

我得到异常com.sun.jersey.api.container.ContainerException：当我运行我的简单应用程序，使用带有泽西的Restfull Web服务打印XML格式的消息 web.xml中：

 <?xml version="1.0" encoding="UTF-8"?>
  <!-- This web.xml file is not required when using Servlet 3.0 container, 
 see implementation details     http://jersey.java.net/nonav/documentation/latest/jax-rs.html#d4e194 -->
  <web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<servlet>
    <servlet-name>Jersey Web Application</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.irfan.javadev.messenger</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
    <servlet-name>Jersey Web Application</servlet-name>
    <url-pattern>/webresources/*</url-pattern>
    </servlet-mapping>
  </web-app>

ServiceLayer： MessageService .java

 public class MessageService {

private Map<Long, Message> messages = DataBaseClass.getMessages();

public List<Message> getAllMessages() {
    return new ArrayList<Message>(messages.values());
   }
 }

DemoDataBase类： DataBaseClass.java

public class DataBaseClass {

    private static Map<Long, Message> messages = new HashMap<Long, Message>();
    private static Map<Long, Profile> profiles = new HashMap<Long, Profile>();


    public static Map<Long, Message> getMessages() {
        return messages;
    }

    public static Map<Long, Profile> getProfiles() {
        return profiles;
    }
 }

消息实体类：Message.java

 @XmlRootElement
 public class Message {

private long id;
private String message;
private Date created;
private String author;

public Message() {
    super();
}
public Message(long id, String message, String author) {
    super();
    this.id = id;
    this.message = message;
    this.author = author;
}
public long getId() {
    return id;
}
public void setId(long id) {
    this.id = id;
}
public String getMessage() {
    return message;
}
public void setMessage(String message) {
    this.message = message;
}
public Date getCreated() {
    return created;
}
public void setCreated(Date created) {
    this.created = created;
}
public String getAuthor() {
    return author;
}
public void setAuthor(String author) {
    this.author = author;
}
}

资源类： MessageResource.java

@Path("/messages")
public class MessageResource {

MessageService msgService = new MessageService();

@GET
@Produces(MediaType.APPLICATION_XML)
public List<Message> getMessage() {
    return msgService.getAllMessages();
}
 }

这个异常背后的原因是什么？ 提前谢谢：）