Chapter 10: JPA Integration

Overview

In previous chapters, we mimic a database with a static list as follows:

public class UserInfoServiceImpl implements UserInfoService,Serializable{

	
	static protected List<User> userList = new ArrayList<User>();  
	static{
		userList.add(new User("anonymous","1234","Anonymous","[email protected]"));
		userList.add(new User("admin","1234","Admin","[email protected]"));
		userList.add(new User("zkoss","1234","ZKOSS","[email protected]"));
	}
	
	/** synchronized is just because we use static userList in this demo to prevent concurrent access **/
	public synchronized User findUser(String account){
		int s = userList.size();
		for(int i=0;i<s;i++){
			User u = userList.get(i);
			if(account.equals(u.getAccount())){
				return User.clone(u);
			}
		}
		return null;
	}
	
...
}

Java Persistence API (JPA) is a POJO-based persistence specification. It offers object-relational mapping solution to enterprise Java applications. In this chapter, we don't create new applications but re-write data persistence part based on chapter 9 with JPA. We will create a simple database with HSQL and implement a persistence layer in DAO (Data Access Object) pattern to encapsulate all database related operations. We also have to annotate all entity classes that will be stored in the database with JPA annotations. To make the example close to a real application, we keep the Spring framework and demonstrate how to integrate Spring with JPA.