Java 如何用EJB3.0实现一个合适的计数器bean?
[编辑]这个问题是“如何使用EJB3和JPA2.0对实体bean进行原子更改”。应该很简单,对吗 我试图根据目前为止得到的答案来修改代码。我正在使用JBoss 6.0.0M2和高超音速(只需下载并调用run.bat) 我的测试用例:创建3个线程,并在一个循环中调用其中一个Java 如何用EJB3.0实现一个合适的计数器bean?,java,jpa,concurrency,jakarta-ee,ejb-3.0,Java,Jpa,Concurrency,Jakarta Ee,Ejb 3.0,[编辑]这个问题是“如何使用EJB3和JPA2.0对实体bean进行原子更改”。应该很简单,对吗 我试图根据目前为止得到的答案来修改代码。我正在使用JBoss 6.0.0M2和高超音速(只需下载并调用run.bat) 我的测试用例:创建3个线程,并在一个循环中调用其中一个testCounterMitLock*()500次。因此,成功的测试应该打印“Anzahl eingetragene Zeilen:1500”(3*500) 我试过: CounterTestVersion ct
testCounterMitLock*()
500次。因此,成功的测试应该打印“Anzahl eingetragene Zeilen:1500”(3*500)
我试过:
CounterTestVersion ct = manager.find(CounterTestVersion.class, 1);
manager.lock(ct, LockModeType.WRITE);
int wert = ct.getWert();
显然不起作用,因为不同的线程可以在应用锁之前更改数据库中的值。所以我试图解决这个问题:
CounterTestVersion ct = manager.find(CounterTestVersion.class, 1);
manager.lock(ct, LockModeType.WRITE);
manager.refresh (ct);
int wert = ct.getWert();
refresh()
应该给我当前值,隐式查询也应该确保对象现在被锁定。没有这样的运气。让我们试试JPA2.0:
CounterTestVersion ct = manager.find(CounterTestVersion.class, 1, LockModeType.WRITE);
int wert = ct.getWert();
那也不行。也许锁不够用
CounterTestVersion ct = manager.find(CounterTestVersion.class, 1, LockModeType.PESSIMISTIC_WRITE);
int wert = ct.getWert();
嗯。。。也不行!最后一次绝望的尝试:
CounterTestVersion ct = manager.find(CounterTestVersion.class, 1, LockModeType.PESSIMISTIC_WRITE);
manager.flush();
manager.refresh (ct);
int wert = ct.getWert();
好的。。。有人能解释为什么什么都不管用吗?我没有主意了
[EDIT2]PS:雪上加霜的是,这是最后一个运行线程的最后一个输出:
commit/rollback: 441/62
(441+62=503)
这是完整的代码。首先是bean:
package server.kap15;
import java.rmi.RemoteException;
import javax.ejb.*;
import javax.persistence.*;
@Stateful
public class CounterTestBean implements CounterTestRemote, SessionSynchronization {
@PersistenceContext(unitName = "JavaEE")
EntityManager manager;
private int commit = 0;
private int rollback = 0;
public void initDatenbank() {
manager.createNamedQuery("CounterTest.deleteAll").executeUpdate();
manager.createNamedQuery("TestTabelle.deleteAll").executeUpdate();
CounterTestVersion ct = new CounterTestVersion();
ct.setNr(1);
ct.setVersion(1);
ct.setWert(1);
manager.persist(ct);
}
public boolean testCounterOhneLock() {
try {
CounterTest ct = manager.find(CounterTest.class, 1);
int wert = ct.getWert();
ct.setWert(wert + 1);
TestTabelle tt = new TestTabelle();
tt.setNr(wert);
manager.persist(tt);
manager.flush();
return true;
} catch (Throwable t) {
return false;
}
}
public boolean testCounterMitLock() {
try {
CounterTestVersion ct = manager.find(CounterTestVersion.class, 1);
manager.lock(ct, LockModeType.WRITE);
int wert = ct.getWert();
ct.setWert(wert + 1);
TestTabelle tt = new TestTabelle();
tt.setNr(wert);
manager.persist(tt);
manager.flush();
return true;
} catch (Throwable t) {
return false;
}
}
public boolean testCounterMitLock2() {
try {
CounterTestVersion ct = manager.find(CounterTestVersion.class, 1);
manager.lock(ct, LockModeType.WRITE);
manager.refresh (ct);
int wert = ct.getWert();
ct.setWert(wert + 1);
TestTabelle tt = new TestTabelle();
tt.setNr(wert);
manager.persist(tt);
manager.flush();
return true;
} catch (Throwable t) {
return false;
}
}
public boolean testCounterMitLock3() {
try {
CounterTestVersion ct = manager.find(CounterTestVersion.class, 1, LockModeType.WRITE);
int wert = ct.getWert();
ct.setWert(wert + 1);
TestTabelle tt = new TestTabelle();
tt.setNr(wert);
manager.persist(tt);
manager.flush();
return true;
} catch (Throwable t) {
return false;
}
}
public boolean testCounterMitLock4() {
try {
CounterTestVersion ct = manager.find(CounterTestVersion.class, 1, LockModeType.PESSIMISTIC_WRITE);
int wert = ct.getWert();
ct.setWert(wert + 1);
TestTabelle tt = new TestTabelle();
tt.setNr(wert);
manager.persist(tt);
manager.flush();
return true;
} catch (Throwable t) {
return false;
}
}
public boolean testCounterMitLock5() {
try {
CounterTestVersion ct = manager.find(CounterTestVersion.class, 1, LockModeType.PESSIMISTIC_WRITE);
manager.flush();
manager.refresh (ct);
int wert = ct.getWert();
ct.setWert(wert + 1);
TestTabelle tt = new TestTabelle();
tt.setNr(wert);
manager.persist(tt);
manager.flush();
return true;
} catch (Throwable t) {
return false;
}
}
public boolean testCounterMitVersion() {
try {
CounterTestVersion ctv = manager.find(CounterTestVersion.class, 1);
int wert = ctv.getWert();
ctv.setWert(wert + 1);
manager.flush();
TestTabelle tt = new TestTabelle();
tt.setNr(wert);
manager.persist(tt);
manager.flush();
return true;
} catch (OptimisticLockException e) {
System.out.println(">>> Versionskonflikt !");
return false;
} catch (Throwable t) {
System.out.println(t.getMessage());
return false;
}
}
public long anzTestZeilen() {
Query query = manager.createNamedQuery("TestTabelle.anzZeilen");
Long anzahl = (Long) query.getSingleResult();
return anzahl;
}
public void afterBegin() throws EJBException, RemoteException {
}
public void beforeCompletion() throws EJBException, RemoteException {
}
public void afterCompletion(boolean committed) throws EJBException,
RemoteException {
if (committed)
commit++;
else
rollback++;
System.out.println("commit/rollback: " + commit + "/" + rollback);
}
}
远程接口:
package server.kap15;
import javax.ejb.Remote;
@Remote
public interface CounterTestRemote {
public void initDatenbank();
public boolean testCounterOhneLock();
public boolean testCounterMitLock();
public boolean testCounterMitLock2();
public boolean testCounterMitLock3();
public boolean testCounterMitLock4();
public boolean testCounterMitLock5();
public boolean testCounterMitVersion();
public long anzTestZeilen();
}
persistence.xml文件:
<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"
version="1.0">
<persistence-unit name="JavaEE">
<jta-data-source>java:DefaultDS</jta-data-source>
</persistence-unit>
</persistence>
java:DefaultDS
测试客户端:
package client.kap15;
import java.util.Properties;
import javax.naming.*;
import javax.rmi.PortableRemoteObject;
import server.kap15.CounterTestRemote;
public class CounterTestMitLock extends Thread {
CounterTestRemote ctr;
public static void main(String[] args) {
try
{
testMitLock();
testMitLock2();
testMitLock3();
testMitLock4();
testMitLock5();
}
catch (Exception e)
{
e.printStackTrace ();
}
}
static int N = 3;
static CounterThread[] ct = new CounterThread[N];
private static void testMitLock () throws InterruptedException
{
System.out.println("--- Counter Test MIT Lock ----------------------");
System.out.println("Testinstanzen erzeugen...");
for (int i=0; i<N; i++)
ct[i] = new CounterThreadMitLock();
runTest ();
}
private static void testMitLock2 () throws InterruptedException
{
System.out.println("--- Counter Test MIT Lock2 ----------------------");
System.out.println("Testinstanzen erzeugen...");
for (int i=0; i<N; i++)
ct[i] = new CounterThreadMitLock2();
runTest ();
}
private static void testMitLock3 () throws InterruptedException
{
System.out.println("--- Counter Test MIT Lock3 ----------------------");
System.out.println("Testinstanzen erzeugen...");
for (int i=0; i<N; i++)
ct[i] = new CounterThreadMitLock3();
runTest ();
}
private static void testMitLock4 () throws InterruptedException
{
System.out.println("--- Counter Test MIT Lock4 ----------------------");
System.out.println("Testinstanzen erzeugen...");
for (int i=0; i<N; i++)
ct[i] = new CounterThreadMitLock4();
runTest ();
}
private static void testMitLock5 () throws InterruptedException
{
System.out.println("--- Counter Test MIT Lock5 ----------------------");
System.out.println("Testinstanzen erzeugen...");
for (int i=0; i<N; i++)
ct[i] = new CounterThreadMitLock5();
runTest ();
}
private static void runTest () throws InterruptedException
{
System.out.println("Datenbank initialisieren...");
ct[0].ctr.initDatenbank();
System.out.println("Test durchführen...");
for (int i=0; i<N; i++)
ct[i].start();
System.out.println("Auf Ende warten...");
for (int i=0; i<N; i++)
ct[i].join();
System.out.println("Anzahl eingetragene Zeilen: " + ct[0].ctr.anzTestZeilen());
}
private static CounterTestRemote verbinden() {
try {
Properties p = new Properties();
p.put(Context.INITIAL_CONTEXT_FACTORY, "org.jnp.interfaces.NamingContextFactory");
p.put(Context.URL_PKG_PREFIXES, "org.jboss.naming:org.jnp.interfaces");
p.put(Context.PROVIDER_URL, "jnp://localhost:1099");
Context ctx = new InitialContext(p);
Object ref = ctx.lookup("CounterTestBean/remote");
CounterTestRemote ctr = (CounterTestRemote) PortableRemoteObject.narrow(ref, CounterTestRemote.class);
return ctr;
} catch (NamingException e) {
System.out.println("ERROR - NamingException!");
System.exit(-1);
}
return null;
}
public abstract static class CounterThread extends Thread
{
protected CounterTestRemote ctr;
public CounterThread ()
{
this.ctr = verbinden ();
}
public void run() {
for (int i = 0; i < 500; i++)
test ();
}
public abstract void test ();
}
public static class CounterThreadMitLock extends CounterThread
{
@Override
public void test ()
{
this.ctr.testCounterMitLock();
}
}
public static class CounterThreadMitLock2 extends CounterThread
{
@Override
public void test ()
{
this.ctr.testCounterMitLock2();
}
}
public static class CounterThreadMitLock3 extends CounterThread
{
@Override
public void test ()
{
this.ctr.testCounterMitLock3();
}
}
public static class CounterThreadMitLock4 extends CounterThread
{
@Override
public void test ()
{
this.ctr.testCounterMitLock4();
}
}
public static class CounterThreadMitLock5 extends CounterThread
{
@Override
public void test ()
{
this.ctr.testCounterMitLock5();
}
}
}
package client.kap15;
导入java.util.Properties;
导入javax.naming.*;
导入javax.rmi.PortableRemoteObject;
导入server.kap15.CounterTestRemote;
公共类CounterTestMitLock扩展线程{
反测试远程ctr;
公共静态void main(字符串[]args){
尝试
{
testMitLock();
testMitLock2();
testMitLock3();
testMitLock4();
testMitLock5();
}
捕获(例外e)
{
e、 printStackTrace();
}
}
静态int N=3;
静态反螺纹[]ct=新反螺纹[N];
私有静态void testMitLock()抛出InterruptedException
{
System.out.println(“----计数器测试MIT锁---------------------”);
System.out.println(“Testinstanzen-erzeugen…”);
对于(int i=0;i您没有显示如何处理testCounterWithLock的返回值。我的猜测是您得到了乐观的锁定失败,并且返回值有时为false
当冲突在实践中可能很少发生时,Optimatic锁定是一种合理的模式,调用方可以合理地重做工作。因此,如果您遇到乐观的失败,您可以重试
或者,使用悲观锁定模型,这将在您读取的点锁定数据库中的行。您可以这样做,我将悲观锁定模式添加到对find()的调用中。使用悲观锁定需要小心,因为这很容易导致错误的并发性和/或死锁。我有几点意见:
- 您当前正在使用乐观锁定,但我在您的实体上没有看到任何
@Version
字段。我认为这不可行
- 如果您希望计数器增加1500倍,不要使用乐观锁定(您不希望任何更新被拒绝并出现
OptimisticLockingException
)而使用悲观锁定
- 吞咽扔掉的东西确实是错误的,你想让容器完成他的工作(但我想你知道这一点)
所以,这里我会用这个来代替:
manager.lock(ct, LockModeType.READ);
然后卸下锁扣(可丢弃的t)
更新:我现在无法测试,但我会使用类似的方法(其余代码不变):
我真的怀疑这是否有效。首先,读锁不会阻止其他线程更新该行。其次,另一个线程可以更新find()和getCounter()之间的行
你是对的,我走得太快了,上面的肯定不是一个解决方案,@ewernli也是对的,JPA1.0不支持悲观锁定策略,你必须依赖数据库来实现这一点(并使用SELECT for UPDATE
语义).不知怎的,我忘记了这一点,对阅读模式造成了很大的混乱。我的错。谢谢你指出这一点
我认为您必须使用LockModeType.WRITE,但也许可以在lock()之后使用em.refresh()来确保实体不过时
使用LockModeType.WRITE
时,在UPDATE
的WHERE
子句中添加用@Version
注释的实体字段,并在更新期间执行并发检查:
UPDATE COUNTERTEST SET COUNTER = ?, OPT_LOCK = ?
WHERE ((ID = ?) AND (OPT_LOCK = ?))
如果WHERE
子句未能匹配记录(因为另一个线程已经更新了实体),则持久性提供程序将抛出OptimisticLockException
换句话说,在lock()
之后刷新实体不会改变任何东西,另一个线程仍然可以在另一个线程修改计数器时刷新同一实体。以自动方式处理乐观锁定的唯一方法是实现重试机制
但是当flush()
抛出a时(和的实例除外),当前事务被标记为回滚,因此不能用于事务目的。因此,每次重试都必须使用新事务执行。在无状态bean中,可以进行递归远程调用,但我认为这在有状态bean中没有意义,因此必须从客户端处理
最后,这并不是很令人满意,在我看来,JPA1.0中处理这个问题的不那么糟糕的方法是使用SELECT FOR UPDATE获得锁。即使使用LockModeType.READ
或LockModeType.WRITE
,JPA1.0也只支持乐观锁。锁的获取仍然可以推迟到comm是时候了,所以你遇到了问题
发件人:
PA 1.0仅支持乐观读取
或
UPDATE COUNTERTEST SET COUNTER = ?, OPT_LOCK = ?
WHERE ((ID = ?) AND (OPT_LOCK = ?))
Account acc = em.find( Account.class, id, PESSIMISTIC );
Query query = em.createNativeQuery("SELECT * ... FOR UPDATE"); // works with most db
Account acc = (Account) query.getSingleResult();
CounterTestVersion ct = manager.find(CounterTestVersion.class, 1, LockModeType.PESSIMISTIC_WRITE);
int wert = ct.getWert();
Query query = manager.createNativeQuery ("select * from COUNTER_TEST where NR = 1 for update", CounterTestVersion.class);
CounterTestVersion ct = (CounterTestVersion)query.getSingleResult ();
int wert = ct.getWert ()+1;
ORA-00054: resource busy and acquire with NOWAIT specified