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java.lang.Objectjavassist.util.proxy.ProxyFactory
public class ProxyFactory
Factory of dynamic proxy classes.
This factory generates a class that extends the given super class and implements
the given interfaces. The calls of the methods inherited from the super class are
forwarded and then invoke()
is called on the method handler
associated with instances of the generated class. The calls of the methods from
the interfaces are also forwarded to the method handler.
For example, if the following code is executed,
ProxyFactory f = new ProxyFactory(); f.setSuperclass(Foo.class); f.setFilter(new MethodFilter() { public boolean isHandled(Method m) { // ignore finalize() return !m.getName().equals("finalize"); } }); Class c = f.createClass(); MethodHandler mi = new MethodHandler() { public Object invoke(Object self, Method m, Method proceed, Object[] args) throws Throwable { System.out.println("Name: " + m.getName()); return proceed.invoke(self, args); // execute the original method. } }; Foo foo = (Foo)c.newInstance(); ((ProxyObject)foo).setHandler(mi);
Then, the following method call will be forwarded to MethodHandler
mi
and prints a message before executing the originally called method
bar()
in Foo
.
foo.bar();
The last three lines of the code shown above can be replaced with a call to
the helper method create
, which generates a proxy class, instantiates
it, and sets the method handler of the instance:
: Foo foo = (Foo)f.create(new Class[0], new Object[0], mi);
To change the method handler during runtime, execute the following code:
MethodHandler mi = ... ; // alternative handler ((ProxyObject)foo).setHandler(mi);
If setHandler is never called for a proxy instance then it will employ the default handler which proceeds by invoking the original method. The behaviour of the default handler is identical to the following handler:
class EmptyHandler implements MethodHandler { public Object invoke(Object self, Method m, Method proceed, Object[] args) throws Exception { return proceed.invoke(self, args); } }
A proxy factory caches and reuses proxy classes by default. It is possible to reset
this default globally by setting static field useCache
to false.
Caching may also be configured for a specific factory by calling instance method
setUseCache(boolean)
. It is strongly recommended that new clients
of class ProxyFactory enable caching. Failure to do so may lead to exhaustion of
the heap memory area used to store classes.
Caching is automatically disabled for any given proxy factory if deprecated instance
method setHandler(MethodHandler)
is called. This method was
used to specify a default handler which newly created proxy classes should install
when they create their instances. It is only retained to provide backward compatibility
with previous releases of javassist. Unfortunately,this legacy behaviour makes caching
and reuse of proxy classes impossible. The current programming model expects javassist
clients to set the handler of a proxy instance explicitly by calling method
ProxyObject.setHandler(MethodHandler)
as shown in the sample code above. New
clients are strongly recommended to use this model rather than calling
setHandler(MethodHandler)
.
A proxy object generated by ProxyFactory
is serializable
if its super class or any of its interfaces implement java.io.Serializable
.
However, a serialized proxy object may not be compatible with future releases.
The serialization support should be used for short-term storage or RMI.
For compatibility with older releases serialization of proxy objects is implemented by
adding a writeReplace method to the proxy class. This allows a proxy to be serialized
to a conventional ObjectOutputStream
and deserialized from a corresponding
ObjectInputStream
. However this method suffers from several problems, the most
notable one being that it fails to serialize state inherited from the proxy's superclass.
An alternative method of serializing proxy objects is available which fixes these problems. It
requires inhibiting generation of the writeReplace method and instead using instances of
ProxyObjectOutputStream
and ProxyObjectInputStream
(which are subclasses of ObjectOutputStream
and ObjectInputStream
)
to serialize and deserialize, respectively, the proxy. These streams recognise javassist proxies and ensure
that they are serialized and deserialized without the need for the proxy class to implement special methods
such as writeReplace. Generation of the writeReplace method can be disabled globally by setting static field
useWriteReplace
to false. Alternatively, it may be
configured per factory by calling instance method setUseWriteReplace(boolean)
.
MethodHandler
Nested Class Summary | |
---|---|
static interface |
ProxyFactory.ClassLoaderProvider
A provider of class loaders. |
Field Summary | |
---|---|
static ProxyFactory.ClassLoaderProvider |
classLoaderProvider
A provider used by createClass() for obtaining
a class loader. |
static boolean |
useCache
If true, a generated proxy class is cached and it will be reused when generating the proxy class with the same properties is requested. |
static boolean |
useWriteReplace
If true, a generated proxy class will implement method writeReplace enabling serialization of its proxies to a conventional ObjectOutputStream. |
java.lang.String |
writeDirectory
If the value of this variable is not null, the class file of the generated proxy class is written under the directory specified by this variable. |
Constructor Summary | |
---|---|
ProxyFactory()
Constructs a factory of proxy class. |
Method Summary | |
---|---|
java.lang.Object |
create(java.lang.Class[] paramTypes,
java.lang.Object[] args)
Creates a proxy class and returns an instance of that class. |
java.lang.Object |
create(java.lang.Class[] paramTypes,
java.lang.Object[] args,
MethodHandler mh)
Creates a proxy class and returns an instance of that class. |
java.lang.Class |
createClass()
Generates a proxy class using the current filter. |
java.lang.Class |
createClass(MethodFilter filter)
Generates a proxy class using the supplied filter. |
java.lang.Class[] |
getInterfaces()
Obtains the interfaces set by setInterfaces . |
java.lang.String |
getKey(java.lang.Class superClass,
java.lang.Class[] interfaces,
byte[] signature,
boolean useWriteReplace)
|
java.lang.Class |
getSuperclass()
Obtains the super class set by setSuperclass() . |
static boolean |
isProxyClass(java.lang.Class cl)
determine if a class is a javassist proxy class |
boolean |
isUseCache()
test whether this factory uses the proxy cache |
boolean |
isUseWriteReplace()
test whether this factory installs a writeReplace method in created classes |
void |
setFilter(MethodFilter mf)
Sets a filter that selects the methods that will be controlled by a handler. |
void |
setHandler(MethodHandler mi)
Deprecated. since 3.12 use of this method is incompatible with proxy class caching. instead clients should call method ProxyObject.setHandler(MethodHandler) to set the handler
for each newly created proxy instance.
calling this method will automatically disable caching of classes created by the proxy factory. |
void |
setInterfaces(java.lang.Class[] ifs)
Sets the interfaces of a proxy class. |
void |
setSuperclass(java.lang.Class clazz)
Sets the super class of a proxy class. |
void |
setUseCache(boolean useCache)
configure whether this factory should use the proxy cache |
void |
setUseWriteReplace(boolean useWriteReplace)
configure whether this factory should add a writeReplace method to created classes |
Methods inherited from class java.lang.Object |
---|
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Field Detail |
---|
public java.lang.String writeDirectory
"."
, then the class file is written under the current
directory. This method is for debugging.
The default value is null.
public static volatile boolean useCache
setUseCache(boolean)
public static volatile boolean useWriteReplace
ProxyObjectOutputStream
and deserialization must be via ProxyObjectInputStream
. Any attempt to serialize
proxies whose class was created with useWriteReplace set to false via a normal
ObjectOutputStream
will fail.
Note that this value merely specifies the initial setting employed by any newly created
proxy factory. The factory setting may be overwritten by calling factory instance method
setUseWriteReplace(boolean)
public static ProxyFactory.ClassLoaderProvider classLoaderProvider
createClass()
for obtaining
a class loader.
get()
on this ClassLoaderProvider
object
is called to obtain a class loader.
The value of this field can be updated for changing the default implementation.
Example:
ProxyFactory.classLoaderProvider = new ProxyFactory.ClassLoaderProvider() { public ClassLoader get(ProxyFactory pf) { return Thread.currentThread().getContextClassLoader(); } };
Constructor Detail |
---|
public ProxyFactory()
Method Detail |
---|
public boolean isUseCache()
public void setUseCache(boolean useCache)
useCache
- true if this factory should use the proxy cache and false if it should not use the cache
java.lang.RuntimeException
- if a default interceptor has been set for the factorypublic boolean isUseWriteReplace()
public void setUseWriteReplace(boolean useWriteReplace)
useWriteReplace
- true if this factory should add a writeReplace method to created classes and false if it
should not add a writeReplace methodpublic static boolean isProxyClass(java.lang.Class cl)
cl
-
public void setSuperclass(java.lang.Class clazz)
public java.lang.Class getSuperclass()
setSuperclass()
.
public void setInterfaces(java.lang.Class[] ifs)
public java.lang.Class[] getInterfaces()
setInterfaces
.
public void setFilter(MethodFilter mf)
public java.lang.Class createClass()
public java.lang.Class createClass(MethodFilter filter)
public java.lang.String getKey(java.lang.Class superClass, java.lang.Class[] interfaces, byte[] signature, boolean useWriteReplace)
public java.lang.Object create(java.lang.Class[] paramTypes, java.lang.Object[] args, MethodHandler mh) throws java.lang.NoSuchMethodException, java.lang.IllegalArgumentException, java.lang.InstantiationException, java.lang.IllegalAccessException, java.lang.reflect.InvocationTargetException
paramTypes
- parameter types for a constructor.args
- arguments passed to a constructor.mh
- the method handler for the proxy class.
java.lang.NoSuchMethodException
java.lang.IllegalArgumentException
java.lang.InstantiationException
java.lang.IllegalAccessException
java.lang.reflect.InvocationTargetException
public java.lang.Object create(java.lang.Class[] paramTypes, java.lang.Object[] args) throws java.lang.NoSuchMethodException, java.lang.IllegalArgumentException, java.lang.InstantiationException, java.lang.IllegalAccessException, java.lang.reflect.InvocationTargetException
paramTypes
- parameter types for a constructor.args
- arguments passed to a constructor.
java.lang.NoSuchMethodException
java.lang.IllegalArgumentException
java.lang.InstantiationException
java.lang.IllegalAccessException
java.lang.reflect.InvocationTargetException
public void setHandler(MethodHandler mi)
ProxyObject.setHandler(MethodHandler)
to set the handler
for each newly created proxy instance.
calling this method will automatically disable caching of classes created by the proxy factory.
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