hibernate与struts2整合中出现问题以及一级缓存查询数据在业务层问题

直接上问题：

　　

org.hibernate.HibernateException: HHH000142: Javassist Enhancement failed: cn.xxx.pojo.Customer
    at org.hibernate.proxy.pojo.javassist.JavassistProxyFactory.getProxy(JavassistProxyFactory.java:130)
    at org.hibernate.tuple.entity.AbstractEntityTuplizer.createProxy(AbstractEntityTuplizer.java:666)
    at org.hibernate.persister.entity.AbstractEntityPersister.createProxy(AbstractEntityPersister.java:4462)
    at org.hibernate.event.internal.DefaultLoadEventListener.createProxyIfNecessary(DefaultLoadEventListener.java:359)
    at org.hibernate.event.internal.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:274)
    at org.hibernate.event.internal.DefaultLoadEventListener.doOnLoad(DefaultLoadEventListener.java:121)
    at org.hibernate.event.internal.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:89)
    at org.hibernate.internal.SessionImpl.fireLoad(SessionImpl.java:1129)
    at org.hibernate.internal.SessionImpl.access$2600(SessionImpl.java:164)
    at org.hibernate.internal.SessionImpl$IdentifierLoadAccessImpl.getReference(SessionImpl.java:2669)
    at org.hibernate.internal.SessionImpl.load(SessionImpl.java:965)
    at cn.xxx.dao.impl.CustomerDaoImpl.findOrderByCst(CustomerDaoImpl.java:45)
    at cn.xxx.dao.impl.CustomerDaoImpl.demo1(CustomerDaoImpl.java:52)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
Caused by: java.lang.NoClassDefFoundError: javassist/util/proxy/Proxy
    at org.hibernate.proxy.pojo.javassist.JavassistProxyFactory.getProxy(JavassistProxyFactory.java:123)
    ... 35 more
Caused by: java.lang.ClassNotFoundException: javassist.util.proxy.Proxy
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    ... 36 more

一开始报出 HibernateException，这个问题原因是：struts2和hibernate整合时，有些jar包冲突原因，如Javassist.jar，保留高版本吧。解决jar报冲突问题后又给报错误了。

18:50:37.720 [main] ERROR org.hibernate.proxy.pojo.javassist.JavassistProxyFactory - HHH000142: Javassist Enhancement failed: cn.xxx.pojo.Customer
java.lang.ClassCastException: cn.xxx.pojo.Customer_$$_javassist_3 cannot be cast to javassist.util.proxy.Proxy
    at org.hibernate.proxy.pojo.javassist.JavassistProxyFactory.getProxy(JavassistProxyFactory.java:123) [hibernate-core-5.0.7.Final.jar:5.0.7.Final]
    at org.hibernate.tuple.entity.AbstractEntityTuplizer.createProxy(AbstractEntityTuplizer.java:666) [hibernate-core-5.0.7.Final.jar:5.0.7.Final]
    at org.hibernate.persister.entity.AbstractEntityPersister.createProxy(AbstractEntityPersister.java:4462) [hibernate-core-5.0.7.Final.jar:5.0.7.Final]
    at org.hibernate.event.internal.DefaultLoadEventListener.createProxyIfNecessary(DefaultLoadEventListener.java:359) [hibernate-core-5.0.7.Final.jar:5.0.7.Final]
    at org.hibernate.event.internal.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:274) [hibernate-core-5.0.7.Final.jar:5.0.7.Final]
    at org.hibernate.event.internal.DefaultLoadEventListener.doOnLoad(DefaultLoadEventListener.java:121) [hibernate-core-5.0.7.Final.jar:5.0.7.Final]
    at org.hibernate.event.internal.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:89) [hibernate-core-5.0.7.Final.jar:5.0.7.Final]
    at org.hibernate.internal.SessionImpl.fireLoad(SessionImpl.java:1129) [hibernate-core-5.0.7.Final.jar:5.0.7.Final]
    at org.hibernate.internal.SessionImpl.access$2600(SessionImpl.java:164) [hibernate-core-5.0.7.Final.jar:5.0.7.Final]
    at org.hibernate.internal.SessionImpl$IdentifierLoadAccessImpl.getReference(SessionImpl.java:2669) [hibernate-core-5.0.7.Final.jar:5.0.7.Final]
    at org.hibernate.internal.SessionImpl.load(SessionImpl.java:965) [hibernate-core-5.0.7.Final.jar:5.0.7.Final]
    at cn.xxx.dao.impl.CustomerDaoImpl.findOrderByCst(CustomerDaoImpl.java:45) [classes/:?]
    at cn.xxx.dao.impl.CustomerDaoImpl.demo1(CustomerDaoImpl.java:53) [classes/:?]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_112]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_112]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_112]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_112]
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50) [junit.jar:4.12]
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) [junit.jar:4.12]
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47) [junit.jar:4.12]
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) [junit.jar:4.12]
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325) [junit.jar:4.12]
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78) [junit.jar:4.12]
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57) [junit.jar:4.12]
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290) [junit.jar:4.12]
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71) [junit.jar:4.12]
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288) [junit.jar:4.12]
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58) [junit.jar:4.12]
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268) [junit.jar:4.12]
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363) [junit.jar:4.12]
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86) [.cp/:?]
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) [.cp/:?]
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459) [.cp/:?]
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678) [.cp/:?]
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382) [.cp/:?]
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192) [.cp/:?]

上代码：

@Override
    public Set<Order> findOrderByCst(Long cstId) {
　　　　　//这里面getSession方法直接获取当前线程的session对象
        Session session = HibernateSessionFactory.getSession();
        Set<Order> orders = session.load(Customer.class, cstId).getOrders();
        return orders;
    }
    
    @Test
    public void demo1(){
        Session session = HibernateSessionFactory.getSession();
        Transaction transaction = session.beginTransaction();
        Set<Order> orders  = findOrderByCst(1L);
        for (Order order : orders) {
            System.out.println(order);
        }
        transaction.commit();
    }

我们知道；对于一些比较复杂的业务，事务都放在业务层开启和关闭，我们经常需要保证连接对象的一致，不然可能导致某些逻辑操作成功另一些失败，不符合原子性。这里有一篇文章介绍的很详细，概念和例子：https://blog.csdn.net/weixin_40657079/article/details/82055822。

那么上面代码就是基于dao层存放操作，service层存放事务。但是现在出现问题，查询一对多的关联对象时候，我用的时load方法，我们知道load是懒加载，他必须在有session的持久态情况才能使用，用的时候才会向数据库发送数据，离开session进入脱管在查询就会报错。

解决办法：

　　1：不用懒加载。

　　　　用get方法或者在配置映射文件配置lazy=false。这里是一对多，一个顾客多个订单，主控方为顾客，关联方为订单，所以在主控方set配置lazy=false（也就是配置关联级别延迟加载）

　　2：离线条件查询（QBC检索）：

　　　　指的是脱离session进行条件查询，如果什么条件都不设置就是查询全部。

　　　　Web层或者Service层获取DetachedCriteria对象，

DetachedCriteria dc = DetachedCriteria.forClass(cCustomer.class)

　　　　dao层：

Criteria criteria = dc.getExecutableCriteria(session);
criteria.list();

　　　　这样照样可以使用懒加载，降低内存消耗