EJB3之JPA程序结构,完美的异常处理
首先得用到封装了基本实体操作的EntityManagerHelper类,这在网上到处都是:
public class EntityManagerHelper {
private static final EntityManagerFactory emf;
private static final ThreadLocal<EntityManager> threadLocal;
private static final Logger logger;
static {
emf = Persistence.createEntityManagerFactory("EjbTestPU");
threadLocal = new ThreadLocal<EntityManager>();
logger = Logger.getLogger("EjbTestPU");
logger.setLevel(Level.ALL);
}
public static EntityManager getEntityManager() {
EntityManager em = threadLocal.get();
if (em == null || !em.isOpen()) {
em = emf.createEntityManager();
threadLocal.set(em);
}
return em;
}
public static void closeEntityManager() {
EntityManager em = threadLocal.get();
threadLocal.set(null);
if (em != null && em.isOpen()) {
em.close();
}
}
public static void beginTransaction() {
getEntityManager().getTransaction().begin();
}
public static void commit() {
getEntityManager().getTransaction().commit();
}
public static void rollback() {
getEntityManager().getTransaction().rollback();
}
public static Query createQuery(String query) {
return getEntityManager().createQuery(query);
}
}
然后呢,所有需要或者不需要事务操作的地方都可以这样写:
try {
EntityManagerHelper.beginTransaction();
// 这里是自己的数据库操作
EntityManagerHelper.commit();
System.out.println("提交成功!");
} catch (Exception e) {
System.out.println("提交异常:" + e);
try {
EntityManagerHelper.rollback();
System.out.println("回滚成功");
} catch (Exception ex) {
System.out.println("回滚异常:" + ex);
}
} finally {
EntityManagerHelper.closeEntityManager();
}
其中重点要注意的地方就是 rollback也需要捕获异常。只有捕获了所有异常,程序才不会“飞”掉。
很显然,如果程序中所有实体操作的地方都这样写,不累死才怪呢,所以可以写这样一个抽象类封装异常处理:
public abstract class Transaction {
final static Logger logger = Logger.getLogger(Transaction.class);
public abstract void run();
public void start() {
try {
EntityManagerHelper.beginTransaction();
run();
EntityManagerHelper.commit();
logger.info("事务提交成功");
} catch (Exception e) {
System.out.println("事务提交异常:" + e);
try {
EntityManagerHelper.rollback();
System.out.println("事务回滚成功");
} catch (Exception ex) {
System.out.println("事务回滚异常:" + ex);
}
} finally {
EntityManagerHelper.closeEntityManager();
}
}
}
使用的时候只需要继承此抽象类即可,例如:
(new Transaction() {
@Override
public void run() {
// 这里是自己的数据库操作
}
}).start();