JPA Integration

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

public class TodoListServiceChapter6Impl implements TodoListService {

    static int todoId = 0;
    static List<Todo> todoList = new ArrayList<Todo>();
    static{
        todoList.add(new Todo(todoId++,"Buy some milk",Priority.LOW,null,null));
        todoList.add(new Todo(todoId++,"Dennis' birthday gift",Priority.MEDIUM,dayAfter(10),null));
        todoList.add(new Todo(todoId++,"Pay credit-card bill",Priority.HIGH,dayAfter(5),"$1,000"));
    }

    /** synchronized is just because we use static userList in this demo to prevent concurrent access **/
    public synchronized List<Todo>getTodoList() {
        List<Todo> list = new ArrayList<Todo>();
        for(Todo todo:todoList){
            list.add(Todo.clone(todo));
        }
        return list;
    }

...
}

• Line 4, 12: Store objects in a static list and perform all data operation on it.

Originally we perform all persistence operations on the list, but we will replace this part with a real database and a persistence framework, JPA.

Java Persistence API (JPA) is a POJO-based persistence specification. It offers an 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 using the 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 using the Spring framework and demonstrate how to integrate Spring with JPA.

Source Code

As we mentioned in the Project Struecture, our source code has 3 branches in github. The source code of this chapter's example belongs to the branch: zk8-jpa.

We don't create new examples in this chapter, but we add 2 DAO classes implemented in JPA under the package org.zkoss.essentials.services.impl.