can any body explain what this exception mean?

Question

I am trying to build a web service based on jersey + JPA + Glasfish 3.1 + java 6u43 + Gson lib for json processing But i am getting a very frustrating exception.

java.lang.ClassCastException: com.hm.model.User cannot be cast to com.hm.model.User

I am not casting user to user but exception shoes me somehow user object is casting back to user . please help me to understand this.

detailed exception snapshot from glasfish server.log

com.sun.jersey.api.core.WebAppResourceConfig|_ThreadID=24;_ThreadName=Thread-1 Scanning for root resource and provider classes in the Web app resource paths:
 /WEB-INF/lib
 /WEB-INF/classes|#]

com.sun.jersey.api.core.ScanningResourceConfig|_ThreadID=24;_ThreadName=Thread-1;|Root resource classes found:
class com.hm.dam.Users|#]

com.sun.jersey.api.core.ScanningResourceConfig|_ThreadID=24;_ThreadName=Thread-1;|No provider classes found.|#]

com.sun.jersey.server.impl.application.WebApplicationImpl|_ThreadID=24;_ThreadName=Thread-1;|Initiating Jersey application, version 'Jersey: 1.5 01/14/2011 12:36 PM'|#]

javax.enterprise.system.container.web.com.sun.enterprise.web|_ThreadID=42;_ThreadName=Thread-1;|WEB0671: Loading application [HMWService] at [/HMWService]|#]

javax.enterprise.system.tools.admin.org.glassfish.deployment.admin|_ThreadID=42;_ThreadName=Thread-1;|HMWService was successfully deployed in 1,100 milliseconds.|#]

javax.enterprise.system.std.com.sun.enterprise.server.logging|_ThreadID=161;_ThreadName=Thread-1;|[EL Fine]: 2013-07-19 01:05:35.01--ServerSession(233673454)--Connection(2052351957)--Thread(Thread[http-thread-pool-8080(4),5,grizzly-kernel])--SELECT user_id, DOB, EMAIL, EXPERIENCE, first_name, inser_user_id, insert_dt, join_dt, last_name, nic_passport, PASSWORD, STATUS, update_dt, update_user_id, USERNAME, gender_ref_id FROM users

com.sun.jersey.spi.container.ContainerResponse|_ThreadID=32;_ThreadName=Thread-1;|The RuntimeException could not be mapped to a response, re-throwing to the HTTP container
java.lang.ClassCastException: com.hm.model.User cannot be cast to com.hm.model.User
at com.hm.dam.Users.read(Users.java:57)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)`

this is how my project structure looks like. i build a JPA project with pojo classes from database containing a table called 'users' this is my pojo and persistence.xml

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence"  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
<persistence-unit name="HMbeans" transaction-type="RESOURCE_LOCAL">
    <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>

    <class>com.hm.model.User</class>
    <exclude-unlisted-classes>false</exclude-unlisted-classes>
    <properties>
        <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/hotel_management"/>
        <property name="javax.persistence.jdbc.user" value="root"/>
        <property name="javax.persistence.jdbc.password" value="123456"/>
        <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
        <property name="eclipselink.logging.level" value="FINER"/>
        <property name="eclipselink.logging.exceptions" value="true"/>
        <property name="eclipselink.logging.session" value="true"/>
        <property name="eclipselink.logging.connection" value="true"/>
    </properties>
</persistence-unit>
</persistence>

Now User entity pojo.

@Entity
@Table(name="users")
public class User implements Serializable {
private static final long serialVersionUID = 1L;

@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
@Column(name="user_id")
private String userId;

@Column(name="first_name")
private String firstName;

@Column(name="last_name")
private String lastName;

private String password;

public User() {
}

public String getUserId() {
    return this.userId;
}

public void setUserId(String userId) {
    this.userId = userId;
}

public String getFirstName() {
    return this.firstName;
}

public void setFirstName(String firstName) {
    this.firstName = firstName;
}

public String getLastName() {
    return this.lastName;
}

public void setLastName(String lastName) {
    this.lastName = lastName;
}   

public String getPassword() {
    return this.password;
}

public void setPassword(String password) {
    this.password = password;
}
}

Now this is my web service class in HMWService dynamic web project

package com.hm.dam;
...

@Path("/users")
public class Users 
{
EntityManager em = JPAUtil.getEntityManager() ;

    @POST
    @Produces(MediaType.APPLICATION_JSON)
    @Path("/readUser")
    public String read(@FormParam("userId") String User_Id) {


       // User u = em.find(User.class, User_Id);
        User u=null;
       Iterator<User> it =  em.createQuery("SELECT u FROM User u").getResultList().iterator();
       if(it.hasNext())
       {
           u=it.next();
           System.out.println(u.getFirstName());
       }
       if(u!=null)
       return new Gson().toJson(u);
       else
           return new Gson().toJson("");

    }      
}

finally this is my web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
<display-name>HMWService</display-name>

<servlet>
    <servlet-name>Jersey Web Application</servlet-name>
    <servlet-class>com.sun.jersey.spi.container.servlet.ServletContainer</servlet-class>
    <load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
    <servlet-name>Jersey Web Application</servlet-name>
    <url-pattern>/rest/*</url-pattern>
</servlet-mapping>
<!--  <persistence-context-ref>
    <persistence-context-ref-name>persistence/em</persistence-context-ref-name>
    <persistence-unit-name>HMentites</persistence-unit-name>
</persistence-context-ref> -->
</web-app>

i write a index.jsp to test the web service . it contains a form with post method. on submit browser show me the above exception

<h1>JAX-RS @FormQuery Testing</h1>

<form action="rest/users/readUser" method="post">
    <p>
        Id : <input type="text" name="userId" />
    </p>

    <input type="submit" value="Read User" />
</form>

exception java.lang.ClassCastException: com.hm.model.User cannot be cast to com.hm.model.User

score 2 · Answer 1 · edited May 23 '17 at 12:22

2

It may be an issue with hot-deployment to your glassfish server (if you use that). Try to clean and build your project and see if this helps.

If it doesn't help this problem usually occurs when a class is loaded by two different Classloaders.

There are a number of different solutions, have a look at this question or this question.

edited May 23 '17 at 12:22

Community

1
1

answered Jul 18 '13 at 21:22

unwichtich

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thanks unwichtich .. your reply gave me direction . yes i was deploying on running server with eclipse. i clean and rebuild the code then exception was gone. but i didn't understand what just happened by cleaning. and how can two Classloaders can use same class. Although i put my JPA entity project as jar file in WEB dynamic project. can you explain me? I also make some changes to persistence.xml and make it to use JTA data source. and try to use built in EJB container for getting persistence entity manager in webservice 'Users' class. Eventually it solved the problem :) – Mubasher Jul 18 '13 at 23:25

can any body explain what this exception mean?

1 Answers1