Persistence4j 是一个非常简单的类库，用于持久化数据至关系数据库中。它个类库可以不需要数据传输对象。只需创建一个POJO，然后利用这个类库简单的保存。这个类库还集成了Java transaction API。支持的数据库包括：Apache Derby ；H2 Database ；HSQLDB ；MySQL ；PostgreSQL。

//First lets create a simple pojo which you like to persist.  @Entity(schema="library",table="book")  public class Book{  @Column(isPrimaryKey=true)  private String isbn;  @Column  private String title;  @Column  private int authorid;  public Book(){    }  public Book(String isbn, String title, int authorid){    this.isbn = isbn;    this.title = title;    this.authorid = authorid;  }  // getters  }    DataProviderFactory dataProviderFactory = new DataProviderFactoryImpl(config);  String databaseName = "library";  String dbmsName = "mysql"  boolean isTransactional = false;  DataProvider dataProvider =  dataProviderFactory.getDataProvider(databaseName, dbmsName, isTransactional);    // Now lets create a object of Book class and persist it  Book book = new Book("123432","TestBook",5);  TransferUtil.registerClass(Book.class);  GenericDAO<Book> genericDAO = new GenericDaoImpl<Book>(dataProvider.getDataFetcher());    //Persist Book  genericDAO.createEntity(book);    //Remove Book  genericDAO.deleteEntity(book);    //Test if Entity Exists  genericDAO.isEntityExists(book);    // findByPrimaryKey  Object obj[] = new Object[1];  obj[0] = "123432";  genericDAO.findByPrimaryKey(Book.class, obj);    //If you want to use transactions.This how to get TransactionService.  //Make sure isTransactional variable should be true and underlying dbms supports ACID.  TransactionService ts = dataProvider.getTransactionService();  try{      ts.beginTransaction();      genericDAO.createEntity(book);      ts.commitTransaction();  }catch(Exception exp){  ts.rollbackTransaction();  }    // Check the GenericDAO interface for all the available methods..  You can extend GenericDAOImpl and override the methods and add your own methods.

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