</pre><strong><span style="font-family:Comic Sans MS;font-size:18px;">今天建了個登入的小專案, 使用c3p0搭配DBUtil連線資料庫,然後使用測試類測試連線資料庫的方法可以連線,但是用servlet呼叫這個方法就報空指標異常.不知道是怎麼回事,估計問題很罕見,網上找半天也找不到出錯的原因.</span></strong><p><strong><span style="font-family:Comic Sans MS;font-size:18px;">部分原始碼是這樣的:</span></strong></p><p><pre name="code" class="java"><strong><span style="font-family:Comic Sans MS;font-size:18px;">//-------------這是連線資料庫的----------------
public class SimpleModule {
	private static DataSource ds;
	
	static {
		ds = new ComboPooledDataSource();
	}
	
	public void insertUser(User u) {
		String createUser = "insert into userinfo values(null,?,?)";
System.out.println("beforeQueryRunner");
		QueryRunner qr = new QueryRunner(ds);
		try {
			qr.update(createUser, u.getUsername(), u.getPassword());
		} catch (SQLException e) {
			e.printStackTrace();
		}
	}
	
	public User getUser(User u) {
		String getUser = "select * from userinfo where username=? and password=?";
System.out.println("beforeqr");
		QueryRunner qr = new QueryRunner(ds);
System.out.println(u);
		User user = null;
		try {
			user = qr.query(getUser, new BeanHandler<User>(User.class), u.getUsername(), u.getPassword());
		} catch (SQLException e) {
			e.printStackTrace();
		}
		return user;
	}</span></strong>
 

<strong><span style="font-family:Comic Sans MS;font-size:18px;">//----這是servlet裡的呼叫getUser的方法---------------
protected void doGet(HttpServletRequest request, HttpServletResponse response) 
			throws ServletException, IOException {
		String userName = request.getParameter("username");
		String password = request.getParameter("password");
		User u = new User();
		u.setUsername(userName);
		u.setPassword(password);
		
		SimpleModule sm = new SimpleModule();
		User user = sm.getUser(u);
}
//------這是測試類裡的方法------------------
	@Test
	public void getUserTest() {
		User u2 = new User();
		u2.setUsername("sdf");
		u2.setPassword("sdf");
		User user = sm.getUser(u2);
		if (user != null) {
			System.out.println(user);
		} else {
			System.out.println("null");
		}
	}</span></strong>
 

<strong><span style="font-family:Comic Sans MS;font-size:18px;">//---------這是報錯的資訊-------------------
五月 11, 2016 11:09:32 下午 com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource 
資訊: Initializing c3p0 pool... com.mchange.v2.c3p0.ComboPooledDataSource [ acquireIncrement -> 3, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, contextClassLoaderSource -> caller, dataSourceName -> y6nvpz9g18hubuj2s97ws|db0359, debugUnreturnedConnectionStackTraces -> false, description -> null, driverClass -> null, extensions -> {}, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, forceSynchronousCheckins -> false, forceUseNamedDriverClass -> false, identityToken -> y6nvpz9g18hubuj2s97ws|db0359, idleConnectionTestPeriod -> 0, initialPoolSize -> 3, jdbcUrl -> null, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 0, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 15, maxStatements -> 0, maxStatementsPerConnection -> 0, minPoolSize -> 3, numHelperThreads -> 3, preferredTestQuery -> null, privilegeSpawnedThreads -> false, properties -> {}, propertyCycle -> 0, statementCacheNumDeferredCloseThreads -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, userOverrides -> {}, usesTraditionalReflectiveProxies -> false ]
五月 11, 2016 11:10:02 下午 com.mchange.v2.resourcepool.BasicResourcePool 
警告: com
 
[email protected]1239c31 -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: 
java.lang.NullPointerException
	at sun.jdbc.odbc.JdbcOdbcDriver.getProtocol(JdbcOdbcDriver.java:524)
	at sun.jdbc.odbc.JdbcOdbcDriver.knownURL(JdbcOdbcDriver.java:493)
	at sun.jdbc.odbc.JdbcOdbcDriver.acceptsURL(JdbcOdbcDriver.java:307)
	at java.sql.DriverManager.getDriver(DriverManager.java:262)
	at com.mchange.v2.c3p0.DriverManagerDataSource.driver(DriverManagerDataSource.java:285)
	at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:161)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:161)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:147)
	at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:202)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1138)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1125)
	at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44)
	at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1870)
	at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)
五月 11, 2016 11:10:02 下午 com.mchange.v2.resourcepool.BasicResourcePool 
警告: Having failed to acquire a resource, [email protected] is interrupting all Threads waiting on a resource to check out. Will try again in response to new client requests.</span></strong>

------------------------更新 16/5/12-----------------------------------------

發現問題了, 測試類的c3p0配置是我配置檔案裡的配置,servlet配置是個莫名其妙的配置,大概是路徑不同吧

<span style="font-family:Comic Sans MS;">Initializing c3p0 pool... com.mchange.v2.c3p0.ComboPooledDataSource [ acquireIncrement -> 2, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, contextClassLoaderSource -> caller, dataSourceName -> y6nvpz9g18ju4qz18rkmtj|1424bf0, debugUnreturnedConnectionStackTraces -> false, description -> null, driverClass -> com.mysql.jdbc.Driver, extensions -> {}, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, forceSynchronousCheckins -> false, forceUseNamedDriverClass -> false, identityToken -> y6nvpz9g18ju4qz18rkmtj|1424bf0, idleConnectionTestPeriod -> 0, initialPoolSize -> 10, jdbcUrl -> jdbc:mysql://localhost:3306/mydata?useUnicode=true&characterEncoding=UTF-8, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 30, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 20, maxStatements -> 0, maxStatementsPerConnection -> 0, minPoolSize -> 5, numHelperThreads -> 3, preferredTestQuery -> null, privilegeSpawnedThreads -> false, properties -> {user=******, password=******}, propertyCycle -> 0, statementCacheNumDeferredCloseThreads -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, userOverrides -> {}, usesTraditionalReflectiveProxies -> false ]</span>

解決方法:

總結:還是不能偷懶啊

(又改了改文章樣式...)