13

使用带有 try-with-resources 构造的 Java 7u5,以下代码似乎会泄漏 jdbc 连接

try (Connection connection = ..; PreparedStatement stmt = ..) {
    stmt.setString(..);
    return stmt.executeUpdate() > 0;
}

下一段代码按预期工作:

int ret = 0;

try (Connection connection = ..; PreparedStatement stmt = ..) {
    stmt.setString(..);
    ret = stmt.executeUpdate();
}

return ret > 0;

似乎在第一种情况下,该Connection.close()方法没有被调用。

我正在使用最新的 mysql 连接器。这是出乎意料的行为,对吗?

测试

以下测试不会打印CLOSED

public class Test implements AutoCloseable {

public static void main(String[] args) throws Exception {
    System.out.println(doTest());
}

private static boolean doTest() throws Exception {
    try (Test test = new Test()) {
        return test.execute() > 0;
    }

}

private int execute() {
    return 1;
}

@Override
public void close() throws Exception {
    System.out.println("CLOSED");
}
}

奇怪的是,如果execute()修改为return 0;thenCLOSED 被打印。

javap -p -c Test.class 输出

    Compiled from "Test.java"
public class Test implements java.lang.AutoCloseable {
  public Test();
    Code:
       0: aload_0
       1: invokespecial #10                 // Method java/lang/Object."<init>":()V
       4: return

  public static void main(java.lang.String[]) throws java.lang.Exception;
    Code:
       0: getstatic     #21                 // Field java/lang/System.out:Ljava/io/PrintStream;
       3: invokestatic  #27                 // Method doTest:()Z
       6: invokevirtual #31                 // Method java/io/PrintStream.println:(Z)V
       9: return

  private static boolean doTest() throws java.lang.Exception;
    Code:
       0: aconst_null
       1: astore_0
       2: aconst_null
       3: astore_1
       4: new           #1                  // class Test
       7: dup
       8: invokespecial #39                 // Method "<init>":()V
      11: astore_2
      12: aload_2
      13: invokespecial #40                 // Method execute:()I
      16: ifle          21
      19: iconst_1
      20: ireturn
      21: iconst_0
      22: aload_2
      23: ifnull        30
      26: aload_2
      27: invokevirtual #44                 // Method close:()V
      30: ireturn
      31: astore_0
      32: aload_2
      33: ifnull        40
      36: aload_2
      37: invokevirtual #44                 // Method close:()V
      40: aload_0
      41: athrow
      42: astore_1
      43: aload_0
      44: ifnonnull     52
      47: aload_1
      48: astore_0
      49: goto          62
      52: aload_0
      53: aload_1
      54: if_acmpeq     62
      57: aload_0
      58: aload_1
      59: invokevirtual #47                 // Method java/lang/Throwable.addSuppressed:(Ljava/lang/Throwable;)V
      62: aload_0
      63: athrow
    Exception table:
       from    to  target type
          12    22    31   any
          30    31    31   any
           4    42    42   any

  private int execute();
    Code:
       0: iconst_1
       1: ireturn

  public void close() throws java.lang.Exception;
    Code:
       0: getstatic     #21                 // Field java/lang/System.out:Ljava/io/PrintStream;
       3: ldc           #55                 // String CLOSED
       5: invokevirtual #57                 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
       8: return
}
4

5 回答 5

3

升级到最新版本的 eclipse (Juno) 后,这种奇怪的行为不再发生。

使用命令行编译和运行它也可以正常工作。

我怀疑 Eclipse Indigo 正在使用旧版本javac进行编译,并且没有抱怨任何合规性违规。

于 2012-07-16T15:36:05.443 回答
2

我在使用 JDK 1.7.0_17 时遇到了同样的问题。经过仔细排除,结果证明我的 IntelliJ 使用的是 AspectJ 编译器。一旦我使用 JDK 的 javac 显式编译了该类,它就会按预期工作。

我的同事已向AspectJ 人员提交了错误报告。他们已经安排了 1.7.3 版的修复

于 2013-03-22T08:05:39.723 回答
1

这是一个 java 7u5 错误;去注册一个错误。 Java 7u4 工作。

return test.execute() > 0;

给出 > 0 的错误代码:

  13: invokespecial #40                 // Method execute:()I
  16: ifle          21
  19: iconst_1
  20: ireturn
于 2012-07-16T15:16:42.880 回答
0

编辑

  1. Eclipse Juno它工作得很好。我不认为这是一个 java 7 错误。从 运行时它不起作用Eclipse Indigo

  2. 它也适用于Command Line.

上一个答案

在以下情况下,我运行您的程序并且它有效,我正在检查您的情况

情况1 :

public class Test implements AutoCloseable {

    public int execute() {
        return 1;
    }

    @Override
    public void close() throws Exception {
        System.out.println("CLOSED");
    }
}



public class Test1 {

    public static void main(String[] args) throws Exception {

        try (Test test = new Test()) {
            System.out.println(test.execute() > 0);
        }

    }

}

输出 :

true
CLOSED

案例2:

public class Test implements AutoCloseable {

    public static void main(String[] args) throws Exception {
        System.out.println(doTest());
    }

    private static boolean doTest() throws Exception {
        try (Test test = new Test()) {
            throw new ArrayIndexOutOfBoundsException("exc"); // just for testing
            //return test.execute() > 0;
        }

    }

    private int execute() {
        return 1;
    }

    @Override
    public void close() throws Exception {
        System.out.println("CLOSED");
    }
}

输出 :

CLOSED
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: exc
    at com.aquent.rambo.auth.Test.doTest(Test.java:11)
    at com.aquent.rambo.auth.Test.main(Test.java:6)

案例3:Here this is wierd, and it works

public class Test implements AutoCloseable {

    public static void main(String[] args) throws Exception {
        System.out.println(doTest());
    }

    private static boolean doTest() throws Exception {
        try (Test test = new Test()) {
            boolean result = test.execute() > 0; // Change : result variable declared
            return result;
        }

    }

    private int execute() {
        return 1;
    }

    @Override
    public void close() throws Exception {
        System.out.println("CLOSED");
    }
}

输出 :

CLOSED
true
于 2012-07-16T15:06:18.650 回答
-3

完成后您是否尝试关闭语句和/或连接。

还要确保在 finally 块中执行此操作:

于 2012-07-16T01:53:55.283 回答