Package 

Class CloseGuard

  • 
public final class CloseGuard

    CloseGuard is a mechanism for flagging implicit finalizer cleanup of resources that should have been cleaned up by explicit close methods (aka "explicit termination methods" in Effective Java).

    A simple example: 

       {@code * class Foo { * * private final CloseGuard guard = CloseGuard.get(); * * ... * * public Foo() { * ...; * guard.open("cleanup"); * } * * public void cleanup() { * guard.close(); * ...; * } * * protected void finalize() throws Throwable { * try { * if (guard != null) { * guard.warnIfOpen(); * } * cleanup(); * } finally { * super.finalize(); * } * } * } * }
    In usage where the resource to be explicitly cleaned up are allocated after object construction, CloseGuard protection can be deferred. For example: 
       {@code * class Bar { * * private final CloseGuard guard = CloseGuard.get(); * * ... * * public Bar() { * ...; * } * * public void connect() { * ...; * guard.open("cleanup"); * } * * public void cleanup() { * guard.close(); * ...; * } * * protected void finalize() throws Throwable { * try { * if (guard != null) { * guard.warnIfOpen(); * } * cleanup(); * } finally { * super.finalize(); * } * } * } * }
    When used in a constructor calls to {@code open} should occur at the end of the constructor since an exception that would cause abrupt termination of the constructor will mean that the user will not have a reference to the object to cleanup explicitly. When used in a method, the call to {@code open} should occur just after resource acquisition.

    Note that the null check on {@code guard} in the finalizer is to cover cases where a constructor throws an exception causing the {@code guard} to be uninitialized.

    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      public interface CloseGuard.Reporter

      Interface to allow customization of reporting behavior.

    • Method Summary

      Modifier and Type Method Description
      static CloseGuard get() Returns a CloseGuard instance.
      static void setEnabled(boolean enabled) Used to enable or disable CloseGuard.
      static void setReporter(CloseGuard.Reporter reporter) Used to replace default Reporter used to warn of CloseGuardviolations.
      static CloseGuard.Reporter getReporter() Returns non-null CloseGuard.Reporter.
      void open(String closer) If CloseGuard is enabled, {@code open} initializes the instancewith a warning that the caller should have explicitly called the {@code closer} method instead of relying on finalization.
      void close() Marks this CloseGuard instance as closed to avoid warnings onfinalization.
      void warnIfOpen() If CloseGuard is enabled, logs a warning if the caller did notproperly cleanup by calling an explicit close methodbefore finalization.

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Method Detail

      • get

         static CloseGuard get()

        Returns a CloseGuard instance. If CloseGuard is enabled, {@code * #open(String)} can be used to set up the instance to warn onfailure to close. If CloseGuard is disabled, a non-null no-opinstance is returned.

      • setEnabled

         static void setEnabled(boolean enabled)

        Used to enable or disable CloseGuard. Note that CloseGuard onlywarns if it is enabled for both allocation and finalization.

      • setReporter

         static void setReporter(CloseGuard.Reporter reporter)

        Used to replace default Reporter used to warn of CloseGuardviolations. Must be non-null.

      • open

         void open(String closer)

        If CloseGuard is enabled, {@code open} initializes the instancewith a warning that the caller should have explicitly called the {@code closer} method instead of relying on finalization.

        Parameters:
        closer - non-null name of explicit termination method

      • close

         void close()

        Marks this CloseGuard instance as closed to avoid warnings onfinalization.

      • warnIfOpen

         void warnIfOpen()

        If CloseGuard is enabled, logs a warning if the caller did notproperly cleanup by calling an explicit close methodbefore finalization. If CloseGuard is disabled, no action isperformed.