一个通用的Hibernate DAO

经过one-to-one和one-to-many测试没有问题，看直接复制到任何需要DAO的工程中使用
代码
强烈建议在实际使用中加个接口

BaseDAO.JAVA

package com.lusm.HibernateSessionFactory;

import java.io.Serializable;

import java.util.List;

import org.hibernate.Query;

import org.hibernate.Session;

public class BaseDAO {

/**

* 添加实体

* @param obj，要添加的实体对象

* @throws Exception

public void add(Object obj) throws Exception{

Session session = null;

try {

session = HibernateSessionFactory.getSession();

session.save(obj);

session.beginTransaction().commit();

if(session!=null){

session.close();

}

} catch (RuntimeException e) {

session.beginTransaction().rollback();

if(session!=null){

session.close();

}

throw e;

}

/**

* 删除实体

* @param obj，要删除的实体

* @throws Exception

public void delete(Object obj) throws Exception{

Session session = null;

try {

//取得session对象

session =HibernateSessionFactory.getSession();

//删除实体

session.delete(obj);

//提交事务

session.beginTransaction().commit();

if(session!=null){

session.close();

}

} catch (Exception e) {

session.beginTransaction().rollback();//事务回滚

if(session!=null){

session.close();

}

throw e;

}

/**

* 更新实体

* @param obj，要更新的实体

* @throws Exception

public void update(Object obj) throws Exception{

Session session=null;

try {

//取得session对象

session=HibernateSessionFactory.getSession();

//删除实体

session.update(obj);

//提交事务

session.beginTransaction().commit();

if(session!=null){

session.close();

}

} catch (Exception e) {

session.beginTransaction().rollback();//事务回滚

if(session!=null){

session.close();

}

throw e;

}

/**

* 根据指定的hql进行查询，并返回查询结果

* @param hql，hql语句

* @return 查询结果

* @throws Exception

public List<?> findByHQL(String hql) throws Exception{

try {

Query queryObject =HibernateSessionFactory.getSession().createQuery(hql);

return queryObject.list();

} catch (Exception e) {

throw e;

}

/**

* 根据指定的实体类型和主键的值，查找实体对象

* @param cls，实体的类

* @param key，主键的值

* @return，查找的实体对象

* @throws Exception

public Object findById(String cls,Serializable key)

throws Exception

{

try {

Object instance = (Object) HibernateSessionFactory.getSession().get(cls, key);

return instance;

} catch (Exception e) {

throw e;

}

HibernateSessionFactory.java 我就不发了，每个工程里都有

值得注意到是：
写代码是必须考虑到效率，资源利用，第一，不要创建无谓的实例，第二，不要写没有必要的返回语句，第三，close是有目的的，不可以滥用，第四，必须考虑到哪一步出错的概率高，必须在下一步先做判断。

如下代码就是很有问题的：

/**

* 添加实体

* @param obj，要添加的实体对象

* @throws Exception

public void add(Object obj) throws Exception{

Session ses=null;

Transaction tx=null;

try {

//取得session对象

ses=HibernateSessionFactory.getSession();

//开始事务

tx=ses.beginTransaction();

//保存实体

ses.save(obj);

//提交事务

tx.commit();

} catch (Exception e) {

tx.rollback();//事务回滚

throw e;

}finally{

//关闭session

HibernateSessionFactory.closeSession();

}

使用one-to-many中执行删除时，你可能会遇到这样的错误

Exception in thread "main" org.hibernate.TransientObjectException: the detached instance passed to delete() had a null identifier
.........

或者

Exception in thread "main" org.hibernate.TransientObjectException: the detached instance passed to delete() had a null identifier

at org.hibernate.event.def.DefaultDeleteEventListener.onDelete(DefaultDeleteEventListener.java:63)

at org.hibernate.impl.SessionImpl.fireDelete(SessionImpl.java:761)

at org.hibernate.impl.SessionImpl.delete(SessionImpl.java:739)

at com.lusm.HibernateSessionFactory.BaseDAO.delete(BaseDAO.java:44)

at com.lusm.main.Del.main(Del.java:19)

或

Exception in thread "main" org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update

at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:71)

at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)

at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:202)

at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:235)

at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:144)

at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:297)

at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:27)

at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:985)

at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:333)

at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:106)

at com.lusm.HibernateSessionFactory.BaseDAO.delete(BaseDAO.java:46)

at com.lusm.main.Del.main(Del.java:18)

Caused by: java.sql.BatchUpdateException: Cannot delete or update a parent row: a foreign key constraint fails (`lusm/test1`, CONSTRAINT `test1_ibfk_1` FOREIGN KEY (`id`) REFERENCES `test` (`id`))

at com.mysql.jdbc.PreparedStatement.executeBatchSerially(PreparedStatement.java:1669)

at com.mysql.jdbc.PreparedStatement.executeBatch(PreparedStatement.java:1085)

at org.hibernate.jdbc.BatchingBatcher.doExecuteBatch(BatchingBatcher.java:58)

at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:195)

9 more

原因是你的xml配置和数据库创建有问题
下面给出一个成功的例子

many
xml config

<?xml version="1.0" encoding="utf-8"?>

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<!--

Mapping file autogenerated by MyEclipse Persistence Tools

-->

<hibernate-mapping>

</id>

<many-to-one name="test" class="com.lusm.test.Test" fetch="select" cascade="save-update" >

</many-to-one>

</property>

</class>

</hibernate-mapping>

code

package com.lusm.test;

/**

* Test1 generated by MyEclipse Persistence Tools

public class Test1 implements java.io.Serializable {

// Fields

private Integer sid;

private Test test;

private String sname;

// Constructors

/** default constructor */

public Test1() {

}

/** minimal constructor */

public Test1(Test test) {

this.test = test;

}

/** full constructor */

public Test1(Test test, String sname) {

this.test = test;

this.sname = sname;

}

// Property accessors

public Integer getSid() {

return this.sid;

}

public void setSid(Integer sid) {

this.sid = sid;

}

public Test getTest() {

return this.test;

}

public void setTest(Test test) {

this.test = test;

}

public String getSname() {

return this.sname;

}

public void setSname(String sname) {

this.sname = sname;

}

one

xml config

<?xml version="1.0" encoding="utf-8"?>

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<!--

Mapping file autogenerated by MyEclipse Persistence Tools

-->

<hibernate-mapping>

</id>

</property>

<key>

</key>

<one-to-many class="com.lusm.test.Test1"/>

</set>

</class>

</hibernate-mapping>

code

package com.lusm.test;

import java.util.HashSet;

import java.util.Set;

/**

* Test generated by MyEclipse Persistence Tools

public class Test implements java.io.Serializable {

// Fields

private Integer id;

private String name;

private Set test1s = new HashSet(0);

// Constructors

/** default constructor */

public Test() {

}

/** full constructor */

public Test(String name, Set test1s) {

this.name = name;

this.test1s = test1s;

}

// Property accessors

public Integer getId() {

return this.id;

}

public void setId(Integer id) {

this.id = id;

}

public String getName() {

return this.name;

}

public void setName(String name) {

this.name = name;

}

public Set getTest1s() {

return this.test1s;

}

public void setTest1s(Set test1s) {

this.test1s = test1s;

}

db sql

create table `lusm`.`test1`(

`sid` INT not null auto_increment,

`id` INT not null,

`sname` varchar(20),

primary key (`sid`),

index(sid),

foreign key(id) references test(id) ON DELETE CASCADE ON UPDATE CASCADE

);

create table `lusm`.`test`(

`id` INT not null auto_increment,

`name` VARCHAR(20),

primary key (`id`)

);

下面给出该示例的两个测试类

insert

package com.lusm.main;

import com.lusm.HibernateSessionFactory.BaseDAO;

import com.lusm.test.Test;

import com.lusm.test.Test1;

public class Main {

/**

* @param args

* @throws Exception

public static void main(String[] args) throws Exception {

Test test = new Test();

test.setName("nihao");

BaseDAO td = new BaseDAO();

td.add(test);

Test1 t1 = new Test1(test);

Test1 t2 = new Test1(test);

Test1 t3 = new Test1(test);

t1.setSid(1);

t2.setSid(2);

t3.setSid(3);

t1.setSname("nihao");

t2.setSname("mfafs");

t3.setSname("acncs");

BaseDAO td1 = new BaseDAO();

td1.add(t1);

td1.add(t2);

td1.add(t3);

}

delete

package com.lusm.main;

import com.lusm.HibernateSessionFactory.BaseDAO;

import com.lusm.test.Test;

public class Del {

/**

* @param args

* @throws Exception

public static void main(String[] args) throws Exception {

Test test = new Test();

test.setId(1);

BaseDAO bd = new BaseDAO();

bd.delete(test);

}

posted on 2009-11-19 16:54 草原和大树阅读(2779) 评论(0) 编辑收藏举报