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In hibernate this error is common.

Caused by: java.lang.ClassNotFoundException: org.slf4j.impl.StaticLoggerBinder
at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:205)

The hibernate distribution package have slf4j-api-x.x.x.jar file which does not have the impl package.

To avoid this error download slf4j-x.x.x.zip / .gz package from http://slf4j.org/download.html.

In this package you will find slf4j-simple-x.x.x.jar which has this org.slf4j.impl package. Add this jar in your classpath and run your application.

package com.vpj;

import java.util.Set;
import com.vpj.Boo;

public class Foo {
   private String fooId;
   private Storing name;
  
   private Set<Boo> boo;
 
   /* Getters & Setters */
}

package com.vpj;

import java.util.Set;
import com.vpj.Foo;

public class Boo {
   private String booId;
   private String name;

   private Set<Foo> foo;

   /* Getters & Setters */
}

.hbm.xml :

...
<class type="com.vpj.Foo">
 <id name="id" column="id">
  <genetator class="increment" />
 </id>
 
 <property name="name" type="string" column="name" />
 
 <set name="boo" table="Foo_Boo">
  <key column="fooId" />
  <many-to-many column="booId" class="Boo" />
 </set>
</class>

<class type="com.vpj.Boo">
 <id name="id" column="id">
  <generator class="increment" />
 </id>

 <property name="name" type="string" column="name" />
 
 <set name="foo" table="Foo_Boo">
  <key column="booId" />
  <many-to-many column="fooId" class="Foo" />
 </set>
</class>
...

 Session session = createMailSession(); // Create session with your 
                                           authentication data
 MimeMessage message = new MimeMessage(session);
 message.setFrom(new InternetAddress("from@vpj.com"));
 message.setRecipients(new InternetAddress("to@vpj.com"));
 message.setSubject("[SUBJECT]");
            
 BodyPart textPart = new MimeBodyPart();
 textPart.setText(emailBody);
 
 Multipart multiPart = new MimeMultipart(); 
 multiPart.addBodyPart(textPart);

 DataSource source = new FileDataSource("[FILE_PATH]");
 
 BodyPart attachmentPart = new MimeBodyPart();
 attachmentPart.setDataHandler(new DataHandler(source));
 attachmentPart.setFileName("[FILE_NAME]");

 multiPart.addBodyPart(attachmentPart);
 
 message.setContent(multiPart);

 Transport.send(message);
 

import java.net.URLEncoder;
import java.util.*;
import javax.mail.*;
import javax.mail.internet.*;

public class MyMail {
 
 private String d_email = "";
 private String d_password = "";
 
 public void sendMail(String tomailid, String subject, String message)
                                           throws Exception {

    Properties mailProps = new Properties();

    mailProps.load( this.getClass().getResourceAsStream("data/MailData.properties"));

    d_email = mailProps.getProperty("smtp.user");
    d_password = mailProps. getProperty("smtp.password");

    Authenticator auth = new SMTPAuthenticator();

    Session session = Session.getInstance(mailProps, auth);

    MimeMessage msg = new MimeMessage(session);
    msg.setHeader("Content-Type", "text/html;");

    InternetAddress from = new InternetAddress(mailProps.get("mail.user").toString(), 
                             "[EMAIL_HEADING]");
    msg.setFrom(from);
    InternetAddress to = new InternetAddress(tomailid);
   
    msg.addRecipient(Message.RecipientType.TO, to);
    msg.addRecipient(Message.RecipientType.BCC, new InternetAddress("emailid@test.in"));
    msg.setSubject(subject);
    msg.setContent(message, "text/html");

    Transport.send(msg); 
 }

 private class SMTPAuthenticator extends Authenticator {
    public PasswordAuthentication getPasswordAuthentication() {
       return new PasswordAuthentication(d_email, d_password);
    }
 }
 
}

import java.io.InputStream;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;

public class StreamToString {

   public static void main(String[] args) throws Exception {
       StreamToString sts = new StreamToString();

       InputStream is = sts.getClass().getResourceAsStream("/data.txt");

       /*
        * Call the method to convert the 
        * stream to string
        */
       System.out.println(sts.convertStreamToString(is));
   }

   public String convertStreamToString(InputStream is) throws IOException {
       /*
        * To convert the InputStream to String
        * we use the BufferedReader.readLine() 
        * method. Each line will appended to a
        * StringBuilder and returned as String.
        */
       if (is != null) {
           StringBuilder sb = new StringBuilder();
           String line = null;

           try {
              BufferedReader reader = new BufferedReader(new InputStreamReader(is, "UTF-8"));
                while ((line = reader.readLine()) != null)
                 sb.append(line).append("\n");
            
           } catch (Exception e) {
                //Do something..
           } finally {
               is.close();
           }
           return sb.toString();
       } else {      
           return "";
       }
   }
}

Gwt [Server & Client Side] :

Models :

Pojos with Serializable implementation

RPC :

RemoteInterface --> Class extends the com.google.gwt.user.client.rpc.RemoteService
RemoteAsynInterface --> Class [RemoteIntefaceName]+"Async"
All the methods in RemoteInterface should defined in this interface with an extra parameter AsyncCallback.

Server : [ServerClass]

Class should implement RemoteInterface and extends com.google.gwt.user.server.rpc.RemoteServiceServlet

web.xml :

Tells the default page.
Also ServletClass & Mapping.

CallBack: [CallbackClass]

This the the class responsible for AJAX type updates to clients from Server (i.e., ServerClass)
CallbackClass Should implements com.google.gwt.user.client.rpc.AsyncCallback
Two methods:
public void onSuccess(T resultToClient)
The interface is parametrized, thus it supports strong typing. We can proceed with logic instead of worrying about type-casting.
public void onFailure(Throwable exception);

Client:

Probably like a Backing-Bean which has all the component's reference/Object that our page should have.
It should implement com.google.gwt.core.client.EntryPoint
This EntryPoint has the method onLoadModule()
We can override this method to load components in our page.

Project XML : [Project_Name.gwt.xml]

Specifies the compiler which is the Entry_point class.
It also specifies the name of other applications [via tag] in the same container, to which this application has the access.
It also has the URL - Servlet Mapping [As in struts-config file], to which URL which servlet/class is invoked.

[Typically like a WSDL file, since this also the remote call]

HTML Page:

GWT will generate this file, no need to take care on this.