我正在尝试插入具有两列的Oracle数据库 -
ID Primary Key varchar2 (4000)
ACCOUNT varchar2 (4000)
我为此编写了一个多线程程序。并且每个帖子每次都使用unique id插入ID column，因为ID是主键。
我在某个方面面临的唯一问题是 - 以下代码，在运行几秒后抛出异常。
1) Null Pointer Exception
2) java.sql.SQLException: Listener refused the connection with the following error:ORA-12519, TNS:no appropriate service handler found
我无法在代码中找到此问题的根本原因，因为一切对我来说都很好。因为我正在关闭每一个连接。那么这个NPE如何被抛出和其他例外呢？
ExecutorService service = Executors.newFixedThreadPool(10);
try {
// queue some tasks
for (int i = 0; i < 100 * 10; i++) {
service.submit(new ThreadTask());
}
service.shutdown();
service.awaitTermination(Long.MAX_VALUE, TimeUnit.SECONDS);
while (!service.isTerminated()) {
}
} catch (InterruptedException e) {
LOG.warn("Threw a Interrupted Exception in" + XMPLoadTest.class.getSimpleName()
+ ".XMPLoadTest: boss told me to stop...Not my fault!!");
}
下面是ThreadTask类 -
class ThreadTask implements Runnable {
private static final String DRIVER = "oracle.jdbc.driver.OracleDriver";
private static final String CONNECTION = "jdbc:oracle:thin:@localhost:1521:ORCL";
private static final String USER = "scott";
private static final String PASSWORD = "tiger";
private static Connection dbConnection = null;
private static PreparedStatement preparedStatement = null;
private static final AtomicInteger id = new AtomicInteger(1);
private final static Logger LOG = Logger.getLogger(ThreadTask.class.getName());
public ThreadTask() {
}
@Override
public void run() {
try {
dbConnection = getDBConnection();
preparedStatement = dbConnection.prepareStatement(Constants.INSERT_ORACLE_SQL);
preparedStatement.setString(1, String.valueOf(id.getAndIncrement()));
preparedStatement.setString(2, Constants.A_ACCOUNT);
preparedStatement.executeUpdate();
} catch (Exception e) {
// NPE getting thrown here/And second exception as well
LOG.error("Threw a SQLException in " + getClass().getSimpleName(), e);
} finally {
if (preparedStatement != null) {
try {
preparedStatement.close();
preparedStatement = null;
} catch (SQLException e) {
//Oouch...
LOG.error("Threw a SQLException in finally block of prepared statement " + getClass().getSimpleName(), e);
}
}
if (dbConnection != null) {
try {
dbConnection.close();
dbConnection = null;
} catch (SQLException e) {
//Better go and look for SQL.
LOG.error("Threw a SQLException in finally block of dbConnection " + getClass().getSimpleName(), e);
}
}
}
}
/**
* Attempts to establish a connection to the given database URL
*
* @return the db connection
*/
private Connection getDBConnection() {
Connection dbConnection = null;
try {
Class.forName(XMP_DRIVER);
dbConnection = DriverManager.getConnection(CONNECTION, USER, PASSWORD);
} catch (ClassNotFoundException e) {
LOG.error("Threw a ClassNotFoundException in " + getClass().getSimpleName(), e);
} catch (SQLException e) {
//DAMN! I'm not....
LOG.error("Threw a SQLException in " + getClass().getSimpleName(), e);
} catch (Exception e) {
LOG.error("Threw a Exception in " + getClass().getSimpleName(), e);
}
return dbConnection;
}
}
我的代码存在任何潜在问题吗？我更担心这个NPE。
堆栈跟踪：
19:14:28,372 ERROR ThreadTask:187 - Threw a SQLException in ThreadTask
java.sql.SQLException: Listener refused the connection with the following error:
ORA-12519, TNS:no appropriate service handler found
at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:458)
at oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:546)
at oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:236)
at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:32)
at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:521)
at java.sql.DriverManager.getConnection(DriverManager.java:322)
at java.sql.DriverManager.getConnection(DriverManager.java:358)
at com.ebay.xmp.lnp.ThreadTask.getDBConnection(XMPLoadTest.java:179)
at com.ebay.xmp.lnp.ThreadTask.run(XMPLoadTest.java:137)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:452)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:314)
at java.util.concurrent.FutureTask.run(FutureTask.java:149)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:897)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:919)
at java.lang.Thread.run(Thread.java:736)
Caused by: oracle.net.ns.NetException: Listener refused the connection with the following error:
ORA-12519, TNS:no appropriate service handler found
at oracle.net.ns.NSProtocol.connect(NSProtocol.java:395)
at oracle.jdbc.driver.T4CConnection.connect(T4CConnection.java:1102)
at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:320)
... 14 more
19:14:28,376 ERROR ThreadTask:139 - Threw a SQLException in ThreadTask
java.lang.NullPointerException
at com.ebay.xmp.lnp.ThreadTask.run(XMPLoadTest.java:137)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:452)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:314)
at java.util.concurrent.FutureTask.run(FutureTask.java:149)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:897)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:919)
at java.lang.Thread.run(Thread.java:736)
答案 0 :(得分：4)
竞争条件是最简单的解释，因为在当前代码中，当多个线程正在运行时，保证dbConnection作为非空值存在。
简单地说，每个ThreadTask对象都可以访问static Connection dbConnection类字段。如果进行评估，我们认为在应用程序启动期间启动了3个线程，并发生以下情况：
Main+----------------------------------------------------------------------(T)
|+Thread1 --dbConnection=getDBConnection()-------------dbConnection=null|
| |
|----------+Thread2 --dbConnection=getDBConnection()--------------------|dbConnection=null
|
|-------------+Thread3--dbConnection=getDBConnection()------------------|preparedStatement.executeUpdate()
在时间（T），由于null将静态变量设置为Thread1，因此Thread3会抛出异常。
*更新*
您需要使用连接池，请查看c3p0
*结束更新*
答案 1 :(得分：0)
我刚刚遇到了非常相同的场景。
我的先决条件场景： 我在Eclipse IDE中使用包含插入操作的Simple Hibernate程序。
此异常曾经在某些输入中发生，而INSERTION则通过我的HIBERNATE程序＆amp;在其他一些投入没有发生。 是的，它听起来很愚蠢和奇怪。
我很困惑，我确实在google n stack over the flow等上查找了答案。 这是一个非常简单的观察，挽救了我的整个一天！
如果你在eclipse＆amp;如果你遇到这样的场景...... 方案： 在Eclipse中，我只是在“Console”选项卡中关闭所有打开的控制台，当我多次执行相同的程序时，该控制台已经构建。他们堆积起来了正如预期的那样，它已经没空了。关闭所有这些解决了我的问题。 这听起来像是一个非常模糊的解决方案。 没关系它是关于为什么发生这种情况的观察，并且异常没有再次发生。
