c3p0-0.9.5.2 语句展开导致抽象方法错误
c3p0-0.9.5.2 Statement unwrap cause abstractmethoderror
我使用的是 c3p0 版本 0.9.5.1。带有此错误的 unwrap() 方法错误：
java.lang.AbstractMethodError: Method
com/mchange/v2/c3p0/impl/NewProxyStatement.unwrap(Ljava/lang/Class;)Ljava/lang/Object;
is abstract at
com.mchange.v2.c3p0.impl.NewProxyStatement.unwrap(NewProxyStatement.java)
这是我的代码：
com.mysql.jdbc.Statement stm = proxyStatement.unwrap(com.mysql.jdbc.Statement.class)
我看到一些 post 说它应该从 0.9.5 开始工作。
它仍然是一个错误吗？
那我怎样才能从c3p0Statement/Connection得到原来的Statement/Connection呢？
非常感谢
您几乎可以肯定在您的应用程序有效 CLASSPATH 中某处有旧版本的 c3p0。请在 INFO 中检查您的日志以获取 c3p0 的横幅，例如
INFO: Initializing c3p0-0.9.5.2 [built 08-December-2015 22:06:04 -0800; debug? true; trace: 10]
为了确保这一点，我刚刚验证了语句解包是否按照 c3p0-0.9.5.2 中的规定工作。很抱歉这是 Scala REPL 代码而不是 Java。这就是方便的地方。但底层操作在 JVM 级别是相同的。
[info] Starting scala interpreter...
[info]
Welcome to Scala version 2.11.5 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_31).
Type in expressions to have them evaluated.
Type :help for more information.
scala> import com.mchange.v2.c3p0._
import com.mchange.v2.c3p0._
scala> val cpds = new ComboPooledDataSource()
Jul 08, 2016 1:44:43 PM com.mchange.v2.log.MLog
INFO: MLog clients using java 1.4+ standard logging.
Jul 08, 2016 1:44:43 PM com.mchange.v2.c3p0.C3P0Registry
INFO: Initializing c3p0-0.9.5.2 [built 08-December-2015 22:06:04 -0800; debug? true; trace: 10]
cpds: com.mchange.v2.c3p0.ComboPooledDataSource = com.mchange.v2.c3p0.ComboPooledDataSource[ identityToken -> 2u6yea9h1khti8o11c1oj2|2407f8d8, dataSourceName -> 2u6yea9h1khti8o11c1oj2|2407f8d8 ]
scala> cpds.setUser("root")
scala> cpds.setJdbcUrl("jdbc:mysql://localhost/test?useSSL=false&serverTimezone=UTC")
scala> val conn = cpds.getConnection()
Jul 08, 2016 1:45:03 PM com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource
INFO: 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 -> 2u6yea9h1khti8o11c1oj2|2407f8d8, debugUnreturnedConnectionStackTraces -> false, description -> null, driverClass -> null, extensions -> {timezone=HKT}, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, forceSynchronousCheckins -> false, forceUseNamedDriverClass -> false, identityToken -> 2u6yea9h1khti8o11c1oj2|2407f8d8, idleConnectionTestPeriod -> 0, initialPoolSize -> 3, jdbcUrl -> jdbc:mysql://localhost/test?useSSL=false&serverTimezone=UTC, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 0, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 15, maxStatements -> 0, maxStatementsPerConnection -> 0, minPoolSize -> 3, numHelperThreads -> 3, preferredTestQuery -> null, privilegeSpawnedThreads -> false, properties -> {user=******}, propertyCycle -> 0, statementCacheNumDeferredCloseThreads -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, userOverrides -> {}, usesTraditionalReflectiveProxies -> false ]
conn: java.sql.Connection = com.mchange.v2.c3p0.impl.NewProxyConnection@6044a933 [wrapping: com.mysql.cj.jdbc.ConnectionImpl@4318f07b]
scala> val proxyStatement = conn.createStatement()
proxyStatement: java.sql.Statement = com.mchange.v2.c3p0.impl.NewProxyStatement@57b482ea [wrapping: com.mysql.cj.jdbc.StatementImpl@b120337]
scala> val nativeStmt = proxyStatement.unwrap(classOf[com.mysql.cj.jdbc.StatementImpl])
nativeStmt: com.mysql.cj.jdbc.StatementImpl = com.mysql.cj.jdbc.StatementImpl@b120337
我正在使用 MySQL Connector/J 版本 6.0.3，它可能比你的更新（因此声明 class 名称不同）。您可以以更加实现-class 中立的方式展开声明：
scala> val nativeStmt2 = proxyStatement.unwrap(classOf[java.sql.Statement])
nativeStmt2: java.sql.Statement = com.mysql.cj.jdbc.StatementImpl@b120337
请注意，Scala 的 classOf[java.sql.Statement] 等同于 Java 的 class 文字，java.sql.Statement.class
我使用的是 c3p0 版本 0.9.5.1。带有此错误的 unwrap() 方法错误：
java.lang.AbstractMethodError: Method com/mchange/v2/c3p0/impl/NewProxyStatement.unwrap(Ljava/lang/Class;)Ljava/lang/Object; is abstract at com.mchange.v2.c3p0.impl.NewProxyStatement.unwrap(NewProxyStatement.java)
这是我的代码：
com.mysql.jdbc.Statement stm = proxyStatement.unwrap(com.mysql.jdbc.Statement.class)
我看到一些 post 说它应该从 0.9.5 开始工作。 它仍然是一个错误吗？
那我怎样才能从c3p0Statement/Connection得到原来的Statement/Connection呢？ 非常感谢
您几乎可以肯定在您的应用程序有效 CLASSPATH 中某处有旧版本的 c3p0。请在 INFO 中检查您的日志以获取 c3p0 的横幅，例如
INFO: Initializing c3p0-0.9.5.2 [built 08-December-2015 22:06:04 -0800; debug? true; trace: 10]
为了确保这一点，我刚刚验证了语句解包是否按照 c3p0-0.9.5.2 中的规定工作。很抱歉这是 Scala REPL 代码而不是 Java。这就是方便的地方。但底层操作在 JVM 级别是相同的。
[info] Starting scala interpreter...
[info]
Welcome to Scala version 2.11.5 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_31).
Type in expressions to have them evaluated.
Type :help for more information.
scala> import com.mchange.v2.c3p0._
import com.mchange.v2.c3p0._
scala> val cpds = new ComboPooledDataSource()
Jul 08, 2016 1:44:43 PM com.mchange.v2.log.MLog
INFO: MLog clients using java 1.4+ standard logging.
Jul 08, 2016 1:44:43 PM com.mchange.v2.c3p0.C3P0Registry
INFO: Initializing c3p0-0.9.5.2 [built 08-December-2015 22:06:04 -0800; debug? true; trace: 10]
cpds: com.mchange.v2.c3p0.ComboPooledDataSource = com.mchange.v2.c3p0.ComboPooledDataSource[ identityToken -> 2u6yea9h1khti8o11c1oj2|2407f8d8, dataSourceName -> 2u6yea9h1khti8o11c1oj2|2407f8d8 ]
scala> cpds.setUser("root")
scala> cpds.setJdbcUrl("jdbc:mysql://localhost/test?useSSL=false&serverTimezone=UTC")
scala> val conn = cpds.getConnection()
Jul 08, 2016 1:45:03 PM com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource
INFO: 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 -> 2u6yea9h1khti8o11c1oj2|2407f8d8, debugUnreturnedConnectionStackTraces -> false, description -> null, driverClass -> null, extensions -> {timezone=HKT}, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, forceSynchronousCheckins -> false, forceUseNamedDriverClass -> false, identityToken -> 2u6yea9h1khti8o11c1oj2|2407f8d8, idleConnectionTestPeriod -> 0, initialPoolSize -> 3, jdbcUrl -> jdbc:mysql://localhost/test?useSSL=false&serverTimezone=UTC, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 0, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 15, maxStatements -> 0, maxStatementsPerConnection -> 0, minPoolSize -> 3, numHelperThreads -> 3, preferredTestQuery -> null, privilegeSpawnedThreads -> false, properties -> {user=******}, propertyCycle -> 0, statementCacheNumDeferredCloseThreads -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, userOverrides -> {}, usesTraditionalReflectiveProxies -> false ]
conn: java.sql.Connection = com.mchange.v2.c3p0.impl.NewProxyConnection@6044a933 [wrapping: com.mysql.cj.jdbc.ConnectionImpl@4318f07b]
scala> val proxyStatement = conn.createStatement()
proxyStatement: java.sql.Statement = com.mchange.v2.c3p0.impl.NewProxyStatement@57b482ea [wrapping: com.mysql.cj.jdbc.StatementImpl@b120337]
scala> val nativeStmt = proxyStatement.unwrap(classOf[com.mysql.cj.jdbc.StatementImpl])
nativeStmt: com.mysql.cj.jdbc.StatementImpl = com.mysql.cj.jdbc.StatementImpl@b120337
我正在使用 MySQL Connector/J 版本 6.0.3，它可能比你的更新（因此声明 class 名称不同）。您可以以更加实现-class 中立的方式展开声明：
scala> val nativeStmt2 = proxyStatement.unwrap(classOf[java.sql.Statement])
nativeStmt2: java.sql.Statement = com.mysql.cj.jdbc.StatementImpl@b120337
请注意，Scala 的 classOf[java.sql.Statement] 等同于 Java 的 class 文字，java.sql.Statement.class