senselogic.sitevision.api.script.proxy

Interface ExceptionSuppressingProxy

All Superinterfaces:

VelocityAccess.ExceptionSuppressingProxyConstants

public interface ExceptionSuppressingProxy
extends VelocityAccess.ExceptionSuppressingProxyConstants

Proxies an object and delegates all interface method invocations to the proxied object in order to ensure that no invocation will throw an exception.

This interface is an exception suppressing implementation of a so called Dynamic proxy. This means it will proxy all methods of an object that are declared in an interface implemented by the object. If a method invocation through this proxy throws an Exception, it will be catched and the default value will be returned (e.g. null, 0, false etc).

Important note! This interface is intended to be used only in contexts where exceptions will cause serious trouble if they arise and the context doesn't provide proper exception handling (e.g. when executing a Velocity template). Suppressing exceptions is generally a really bad idea and using this proxy will affect performance. Hence, this interface should only be used where the upsides with suppressing exceptions far outweighs the downsides. This interface should be used only as a temporary patch/solution until the "real" problem causing the exception has been solved.

The state of an ExceptionSuppressingProxy is available at all times and updated for each method invocation (except for invocations of methods declared in this interface). If last method invocation resulted in a thrown exception the proxy status will be EXCEPTION_THROWN_STATUS and the exception will be available via getCurrentException().

An instance of the Sitevision class implementing this interface can be obtained via Utils.getExceptionSuppressingProxy(Object). See Utils for how to obtain an instance of the Utils interface.

----------------------------------------------------------------------------------------------------

Example of how ExceptionSuppressingProxy could be used in Velocity:

Case description:

You have a Velocity template where a certain method invocation sometimes throws an exception. The rendered output of the template gets corrupt whenever an exception is thrown and you have not yet tracked down the root cause of the exception. Until the root cause is found and the problem is fixed, you need a temporary solution that ignores exceptions to keep template output acceptable. Since the method is declared in an interface and implemented in the instance you're invoking, you're in sheer luck. You can use an ExceptionSuppressingProxy to suppress exceptions in order to diminish output problems.

This is what the code looks like before your temporary fix:

    <p>
       $myObject.thisNeverThrowsExceptions()
       $myObject.thisMethodSometimesThrowsExceptions() ## This method is declared in an interface, hence can be proxied
    </p>
 

This is how you could use an ExceptionSuppressingProxy to apply a temporary fix:

    <p>
       $myObject.thisNeverThrowsExceptions()

       ## Get an ExceptionSuppressingProxy instance for myObject
       #set ($proxy = $sitevisionUtils.getExceptionSuppressingProxy($myObject))

       $!proxy.thisMethodSometimesThrowsExceptions() ## Method invoked through a proxy, might return null
    </p>
 

Since:

Sitevision 2.6.1_09

Author:

Magnus Lövgren

Field Summary

Fields

Modifier and Type	Field and Description
static int	EXCEPTION_THROWN_STATUS The status indicating that last method invocation did throw an exception
static int	NO_EXCEPTION_THROWN_STATUS The status indicating that last method invocation did not throw an exception.
static int	NO_OBJECT_PROXIED_STATUS The status indicating that this proxy has no object set, nothing to proxy.

Method Summary

Modifier and Type	Method and Description
Exception	getCurrentException() Returns the exception that was thrown during last method invocation of the proxied object.
int	getCurrentStatus() Returns current status
Object	getProxiedObject() Returns the proxied object

Methods inherited from interface senselogic.sitevision.api.render.velocity.VelocityAccess.ExceptionSuppressingProxyConstants

getEXCEPTION_THROWN_STATUS, getNO_EXCEPTION_THROWN_STATUS, getNO_OBJECT_PROXIED_STATUS

Field Detail

NO_OBJECT_PROXIED_STATUS

static final int NO_OBJECT_PROXIED_STATUS

The status indicating that this proxy has no object set, nothing to proxy.

See Also:

Constant Field Values

NO_EXCEPTION_THROWN_STATUS

static final int NO_EXCEPTION_THROWN_STATUS

The status indicating that last method invocation did not throw an exception.

See Also:

Constant Field Values

EXCEPTION_THROWN_STATUS

static final int EXCEPTION_THROWN_STATUS

The status indicating that last method invocation did throw an exception

See Also:

Constant Field Values

Method Detail

getCurrentStatus

int getCurrentStatus()

Returns current status

Returns:

NO_OBJECT_PROXIED_STATUS or NO_EXCEPTION_THROWN_STATUS or EXCEPTION_THROWN_STATUS

getCurrentException

Exception getCurrentException()

Returns the exception that was thrown during last method invocation of the proxied object.

Returns:

the exception thrown during last method invocation, or null if no exeption was thrown

getProxiedObject

Object getProxiedObject()

Returns the proxied object

Returns:

the object that is proxied by an instance of this interface, or null if no proxied object is set