java - 为什么此代码不关闭 JDBC 连接？ (Java 7 可自动关闭的意外行为)

Question

使用 Java 7u5 和 try-with-resources 结构，以下代码似乎会泄漏 jdbc 连接:

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

下一段代码按预期和预期工作:

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，Connection.close() 方法没有被调用。

我正在使用最新的 mysql 连接器。这是意外行为，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() 被修改为 return 0; 那么 CLOSED WILL 会被打印出来。

javap -p -c 测试类输出

    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
}

Answer 1

升级到最新版本的eclipse(Juno)后，这种奇怪的行为就不再发生了。

使用命令行编译运行也能正常工作。

我怀疑 Eclipse Indigo 使用旧的 javac 进行编译，并且没有提示任何违规行为。