Hibernate Map mapping

Introduction

A map stores elements in key-value pairs in a Java collection. No duplicate elements will be accepted. The map interface allows the mapped contents to be represented as a collection of values or a set of key-value mappings, or as a set of keys (keys alone). java.util. An unordered map can be initialized with the help of a hash map. It is indicated by the <map> element in the mapping table.

A Map is mapped with a <map> element in the mapping table and an unordered map can be initialized with java.util.HashMap.

Let us take an example and understand Hibernate Map mapping.

Example on Hibernate Map mapping

We need to create the given below pages for mapping map elements.

1. Question.java
2. hibernate.cfg.xml
3. question.hbm.xml
4. FetchTest.java
5. StoreTest.java

Question.java

import java.util.Map;  
  
public class Question {  
private int id;  
private String name,userName;  
private Map<String,String> answer;  
  
public Question() {}  
public Question(String name, String userName, Map<String, String> answer) {  
    super();  
    this.name = name;  
    this.userName = userName;  
    this.answer = answer;  
}  
public int getId() {  
    return id;  
}  
public void setId(int id) {  
    this.id = id;  
}  
public String getName() {  
    return name;  
}  
public void setName(String name) {  
    this.name = name;  
}  
public String getUsername() {  
    return userName;  
}  
public void setUsername(String username) {  
    this.userName = userName;  
}  
public Map<String, String> getAnswers() {  
    return answer;  
}  
public void setAnswers(Map<String, String> answer) {  
    this.answers = answer;  
}  
}  

question.hbm.xml

<?xml version='1.0' encoding='UTF-8'?>  
<!DOCTYPE hibernate-mapping PUBLIC  
          "-//Hibernate/Hibernate Mapping DTD 5.3//EN"  
          "http://hibernate.sourceforge.net/hibernate-mapping-5.3.dtd">  
            
<hibernate-mapping>  
  
<class name="com.codingninjas.Question" table="question736">  
<id name="id">  
<generator class="native"></generator>  
</id>  
<property name="name"></property>  
<property name="username"></property>  
  
<map name="answers" table="answer736" cascade="all">  
<key column="questionid"></key>  
<index column="answer" type="string"></index>  
<element column="username" type="string"></element>  
</map>  
</class>  
  
</hibernate-mapping>   

hibernate.cfg.xml

<?xml version='1.0' encoding='UTF-8'?>  
<!DOCTYPE hibernate-configuration PUBLIC  
          "-//Hibernate/Hibernate Configuration DTD 5.3//EN"  
          "http://hibernate.sourceforge.net/hibernate-configuration-5.3.dtd">  
  
<hibernate-configuration>  
  
    <session-factory>  
        <property name="hbm2ddl.auto">update</property>  
        <property name="dialect">org.hibernate.dialect.Oracle9Dialect</property>  
        <property name="connection.url">jdbc:oracle:thin:@localhost:1521:xe</property>  
        <property name="connection.username">system</property>  
        <property name="connection.password">jtp</property>  
        <property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>  
      
    <mapping resource="question.hbm.xml"/>  
    </session-factory>  
  
</hibernate-configuration> 

StoreTest.java

import java.util.HashMap;    
import org.hibernate.*;  
import org.hibernate.boot.Metadata;  
import org.hibernate.boot.MetadataSources;  
import org.hibernate.boot.registry.StandardServiceRegistry;  
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;    
  
  
public class StoreTest {    
public static void main(String[] args) {    
   
    StandardServiceRegistry ssr=new StandardServiceRegistryBuilder().configure("hibernate.cfg.xml").build();  
    Metadata meta=new MetadataSources(ssr).getMetadataBuilder().build();  
      
    SessionFactory factory=meta.getSessionFactoryBuilder().build();  
    Session session=factory.openSession();  
   
Transaction t=session.beginTransaction();    
    
HashMap<String,String> map1=new HashMap<String,String>();    
map1.put("Java is a programming language","Rakesh Kumar");    
map1.put("Java is a platform","Vinod Singh");    
    
HashMap<String,String> map2=new HashMap<String,String>();    
map2.put("Servlet technology is a server side programming","Rakesh Kumar");    
map2.put("Servlet is an Interface","Vinod Singh");    
map2.put("Servlet is a package","Charlie Milton");    
    
Question question1=new Question("What is Java?","Aryan",map1);    
Question question2=new Question("What is Servlet?","Anil Kumar",map2);    
    
session.persist(question1);    
session.persist(question2);    
    
t.commit();    
session.close();    
System.out.println("successfully stored");    
}    
}

FetchTest.java

import java.util.*;    
import javax.persistence.TypedQuery;  
import org.hibernate.*;  
import org.hibernate.boot.Metadata;  
import org.hibernate.boot.MetadataSources;  
import org.hibernate.boot.registry.StandardServiceRegistry;  
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;  
   
public class FetchTest {    
public static void main(String[] args) {    
    StandardServiceRegistry ssr=new StandardServiceRegistryBuilder().configure("hibernate.cfg.xml").build();  
    Metadata meta=new MetadataSources(ssr).getMetadataBuilder().build();  
      
    SessionFactory factory=meta.getSessionFactoryBuilder().build();  
    Session session=factory.openSession();    
            
 TypedQuery query=session.createQuery("from Question ");    
 List<Question> list=query.getResultList();    
            
 Iterator<Question> iterator=list.iterator();    
 while(iterator.hasNext()){    
  Question question=iterator.next();    
  System.out.println("question id:"+question.getId());    
  System.out.println("question name:"+question.getName());    
  System.out.println("question posted by:"+question.getUsername());    
  System.out.println("answers.....");    
  Map<String,String> map=question.getAnswers();    
  Set<Map.Entry<String,String>> set=map.entrySet();    
                
  Iterator<Map.Entry<String,String>> iteratoranswer=set.iterator();    
  while(iteratoranswer.hasNext()){    
   Map.Entry<String,String> entry=(Map.Entry<String,String>)iteratoranswer.next();    
   System.out.println("answer name:"+entry.getKey());    
   System.out.println("answer posted by:"+entry.getValue());    
  }    
 }    
session.close();    
}    
}

Output

question id:1
question name: What is Java?
question posted by: Aryan
answers…..
answer name: Java is a programming language
answer posted by: Rakesh Kumar
answer name: Java is a platform
answer posted by: Vinod Singh 
question id: 2
question name: What is Servlet?
question posted by: Anil Kumar
answers…..
answer name: Servlet is a package
answer posted by: Charlie Milton
answer name: Servlet technology is a server side programming
answer posted by: Rakesh Kumar
answer name: Servlet is an Interface
answer posted by: Vinod Singh