Proxy

ProxyProxetta

Once when pointcuts and advices are defined, it is easy to define a proxy aspect itself:

ProxyAspect aspect = ProxyAspect.of(LogProxyAdvice.class, pointcut);

ProxyAspect is nothing but a simple holder of the advice and pointcuts, used for creating Proxetta implementations.

This page describes ProxyProxetta type of proxies, but many things here are common for other Proxetta types as well. {: .attn}

Creating Proxetta (step 1)

For each type of Proxetta, there is a static factory method (yes, you can use new instead if that is your thing):

Proxetta.proxyProxetta();
Proxetta.wrapperProxetta();
Proxetta.invokeProxetta();

Each method returns specific Proxetta builder. Just continue using it by following the fluent interface. Yes, it's that simple.

Let's create a new ProxyProxetta:

ProxyProxetta proxetta =  Proxetta
    .proxyProxetta()
    .withAspect(aspect1)
    .withAspect(aspect2);

Now it's time to configure created ProxyProxetta - or you can just skip the next step and go with the defaults.

Proxetta configuration (step 2)

Each Proxetta implementation share the same set of properties.

forced

Specifies 'forced' mode. If true, the new proxy class will be created even if there are no matching pointcuts. Otherwise, new proxy class will be created only if there is at least one matching pointcut.

classLoader

Specifies classloaders for loading created classes.

variableClassName

Defines variable proxy class name, so every time when new proxy class is created its name will be different. Therefore, one classloader may load it without a problem. If this flag is not set, proxy class name will be constant; Such class can be loaded only once by a classloader.

classNameSuffix

Defines class name suffix of generated classes.

debugFolder

When debug folder is set, Proxetta will save all classes upon their creation into that folder. Very useful for debugging purposes!

Creating Proxy (step 3)

Finally, once when Proxetta is created and configured, we can re-use it multiple times to create a factory for proxies. Proxetta proxy factories are responsible for creating proxy classes using bytecode manipulation.

The proxy factory then can be applied to the target class:

proxetta.proxy().setTarget(targetClass);

The following factory methods are available for creating a proxy class:

• create() - generates class and returns its byte[] content.

• define() - loads created class bytes and returns as a Class.

• newInstance() - instantiates default constructor for defined class.

So the previous line becomes:

Class fooClass = proxetta.proxy().setTarget(Foo.class).define();

or, directly an instance:

Foo foo = proxetta.proxy().setTarget(Foo.class).newInstance();

Note: generated classes do not contain any debug information to avoid ClassFormatError. Some 3rd party tools (like Emma) may loose some local variable information. {: .attn}

ProxyProxetta overview

ProxyProxetta extends a target class. Pointcut method are overridden in proxy. During the execution of adviced code in generated method, target method is called using super reference. Proxy methods has the same annotations as the target methods.

Proxy class has the same constructors as the target class. It is also of the same type as the target class, so it can easily can be used instead.

Obviously, you can't proxy interfaces or abstract methods.

Proxy name

By default, proxy name is created from target class name, by appending default suffix. Suffix name can be changed. Moreover, if variable names feature is turned on, added suffix is changed each time by appending auto-incrementing number. In all cases, proxy class is in the same package as target class.

Sometimes it is needed to have more control over proxy class name and package. This is especially important when proxyfing JDK classes, since default classloader doesn't allow to instantiate anything from java.* package.

Proxetta allows to completely control proxy names. Every method for proxy definition and proxy creation accept second argument that defines proxy name in the following ways:

• .Foo (class name starts with a dot) - proxy package name is equal to

  target package, just proxy simple class name is set.

• foo. (class name ends with a dot) - proxy package is set, proxy

  simple name is create from target simple class name (suffix is

  appended).

• foo.Foo - full proxy class name is specified (suffix is appended).

Adding suffix can be also completely disabled, but in that case different package for proxy class must be provided, since it is not possible to define two classes with the same package and simple names.

Proxy name is set on builder using setTargetProxyClassName().

Integration with Petite

It is easy to apply aspects on beans registered in the Petite container transparently. Petite has single point method for beans registration. User may override this method and create proxy for each bean type before it is actually registered in the container.

There is already a class that does that: ProxettaAwarePetiteContainer.