Class ProxyFactory
- java.lang.Object
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- javassist.util.proxy.ProxyFactory
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public class ProxyFactory extends Object
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(); ((Proxy)foo).setHandler(mi);Here,
Methodisjava.lang.reflect.Method.Then, the following method call will be forwarded to MethodHandler
miand prints a message before executing the originally called methodbar()inFoo.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 ((Proxy)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
useCacheto false. Caching may also be configured for a specific factory by calling instance methodsetUseCache(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 methodProxy.setHandler(MethodHandler)as shown in the sample code above. New clients are strongly recommended to use this model rather than callingsetHandler(MethodHandler).A proxy object generated by
ProxyFactoryis serializable if its super class or any of its interfaces implementjava.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
ObjectOutputStreamand deserialized from a correspondingObjectInputStream. 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
ProxyObjectOutputStreamandProxyObjectInputStream(which are subclasses ofObjectOutputStreamandObjectInputStream) 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 fielduseWriteReplaceto false. Alternatively, it may be configured per factory by calling instance methodsetUseWriteReplace(boolean).- Since:
- 3.1
- Author:
- Muga Nishizawa, Shigeru Chiba, Andrew Dinn
- See Also:
MethodHandler
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Nested Class Summary
Nested Classes Modifier and Type Class Description static interfaceProxyFactory.ClassLoaderProviderA provider of class loaders.static interfaceProxyFactory.UniqueNameA unique class name generator.
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Field Summary
Fields Modifier and Type Field Description static ProxyFactory.ClassLoaderProviderclassLoaderProviderA provider used bycreateClass()for obtaining a class loader.static ProxyFactory.UniqueNamenameGeneratorA unique class name generator.static booleanonlyPublicMethodsIf true, only public/protected methods are forwarded to a proxy object.static booleanuseCacheIf true, a generated proxy class is cached and it will be reused when generating the proxy class with the same properties is requested.static booleanuseWriteReplaceIf true, a generated proxy class will implement method writeReplace enabling serialization of its proxies to a conventional ObjectOutputStream.StringwriteDirectoryIf 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.
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Constructor Summary
Constructors Constructor Description ProxyFactory()Constructs a factory of proxy class.
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Deprecated Methods Modifier and Type Method Description Objectcreate(Class<?>[] paramTypes, Object[] args)Creates a proxy class and returns an instance of that class.Objectcreate(Class<?>[] paramTypes, Object[] args, MethodHandler mh)Creates a proxy class and returns an instance of that class.Class<?>createClass()Generates a proxy class using the current filter.Class<?>createClass(MethodHandles.Lookup lookup)Generates a proxy class using the current filter.Class<?>createClass(MethodHandles.Lookup lookup, MethodFilter filter)Generates a proxy class using the supplied filter.Class<?>createClass(MethodFilter filter)Generates a proxy class using the supplied filter.static MethodHandlergetHandler(Proxy p)Obtains the method handler of the given proxy object.Class<?>[]getInterfaces()Obtains the interfaces set bysetInterfaces.StringgetKey(Class<?> superClass, Class<?>[] interfaces, byte[] signature, boolean useWriteReplace)Class<?>getSuperclass()Obtains the super class set bysetSuperclass().static booleanisProxyClass(Class<?> cl)determine if a class is a javassist proxy classbooleanisUseCache()test whether this factory uses the proxy cachebooleanisUseWriteReplace()test whether this factory installs a writeReplace method in created classesvoidsetFilter(MethodFilter mf)Sets a filter that selects the methods that will be controlled by a handler.voidsetGenericSignature(String sig)Sets the generic signature for the proxy class.voidsetHandler(MethodHandler mi)Deprecated.since 3.12 use of this method is incompatible with proxy class caching.voidsetInterfaces(Class<?>[] ifs)Sets the interfaces of a proxy class.voidsetSuperclass(Class<?> clazz)Sets the super class of a proxy class.voidsetUseCache(boolean useCache)configure whether this factory should use the proxy cachevoidsetUseWriteReplace(boolean useWriteReplace)configure whether this factory should add a writeReplace method to created classes
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Field Detail
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onlyPublicMethods
public static boolean onlyPublicMethods
If true, only public/protected methods are forwarded to a proxy object. The class for that proxy object is loaded by the
defineClassmethod injava.lang.invoke.MethodHandles.Lookup, which is available in Java 9 or later. This works even whensun.misc.Unsafeis not available for some reasons (it is already deprecated in Java 9).To load a class, Javassist first tries to use
sun.misc.Unsafeand, if not available, it uses aprotectedmethod injava.lang.ClassLoaderviaPrivilegedAction. Since the latter approach is not available any longer by default in Java 9 or later, the JVM argument--add-opens java.base/java.lang=ALL-UNNAMEDmust be given to the JVM when it is used (because of lack ofsun.misc.Unsafe). If this argument cannot be given to the JVM,onlyPublicMethodsshould be set totrue. Javassist will try to load by usingjava.lang.invoke.MethodHandles.Lookup.The default value is
false.- Since:
- 3.22
- See Also:
DefineClassHelper.toClass(String, Class, ClassLoader, ProtectionDomain, byte[])
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writeDirectory
public 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. For example, if the value is".", then the class file is written under the current directory. This method is for debugging.The default value is null.
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useCache
public static volatile 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. The default value is true. 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 methodsetUseCache(boolean)- Since:
- 3.4
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useWriteReplace
public static volatile boolean useWriteReplace
If true, a generated proxy class will implement method writeReplace enabling serialization of its proxies to a conventional ObjectOutputStream. this (default) setting retains the old javassist behaviour which has the advantage that it retains compatibility with older releases and requires no extra work on the part of the client performing the serialization. However, it has the disadvantage that state inherited from the superclasses of the proxy is lost during serialization. if false then serialization/deserialization of the proxy instances will preserve all fields. However, serialization must be performed via aProxyObjectOutputStreamand deserialization must be viaProxyObjectInputStream. Any attempt to serialize proxies whose class was created with useWriteReplace set to false via a normalObjectOutputStreamwill 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 methodsetUseWriteReplace(boolean)- Since:
- 3.4
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classLoaderProvider
public static ProxyFactory.ClassLoaderProvider classLoaderProvider
A provider used bycreateClass()for obtaining a class loader.get()on thisClassLoaderProviderobject 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(); } };- Since:
- 3.4
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nameGenerator
public static ProxyFactory.UniqueName nameGenerator
A unique class name generator. Replacing this generator changes the algorithm to generate a unique name. Thegetmethod does not have to be asynchronizedmethod since the access to this field is mutually exclusive and thus thread safe.
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Method Detail
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isUseCache
public boolean isUseCache()
test whether this factory uses the proxy cache- Returns:
- true if this factory uses the proxy cache otherwise false
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setUseCache
public void setUseCache(boolean useCache)
configure whether this factory should use the proxy cache- Parameters:
useCache- true if this factory should use the proxy cache and false if it should not use the cache- Throws:
RuntimeException- if a default interceptor has been set for the factory
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isUseWriteReplace
public boolean isUseWriteReplace()
test whether this factory installs a writeReplace method in created classes- Returns:
- true if this factory installs a writeReplace method in created classes otherwise false
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setUseWriteReplace
public void setUseWriteReplace(boolean useWriteReplace)
configure whether this factory should add a writeReplace method to created classes- Parameters:
useWriteReplace- true if this factory should add a writeReplace method to created classes and false if it should not add a writeReplace method
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isProxyClass
public static boolean isProxyClass(Class<?> cl)
determine if a class is a javassist proxy class- Parameters:
cl-- Returns:
- true if the class is a javassist proxy class otherwise false
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setSuperclass
public void setSuperclass(Class<?> clazz)
Sets the super class of a proxy class.
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getSuperclass
public Class<?> getSuperclass()
Obtains the super class set bysetSuperclass().- Since:
- 3.4
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setInterfaces
public void setInterfaces(Class<?>[] ifs)
Sets the interfaces of a proxy class.
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getInterfaces
public Class<?>[] getInterfaces()
Obtains the interfaces set bysetInterfaces.- Since:
- 3.4
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setFilter
public void setFilter(MethodFilter mf)
Sets a filter that selects the methods that will be controlled by a handler.
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setGenericSignature
public void setGenericSignature(String sig)
Sets the generic signature for the proxy class.For example,
class NullPtr<T> { T get() { return null; } }The following code makes a proxy for
NullPtr<String>:ProxyFactory factory = new ProxyFactory(); factory.setSuperclass(NullPtr.class); factory.setGenericSignature("LNullPtr<Ljava/lang/String;>;"); NullPtr<?> np = (NullPtr<?>)factory.create(null, null); java.lang.reflect.Type[] x = ((java.lang.reflect.ParameterizedType)np.getClass().getGenericSuperclass()) .getActualTypeArguments(); // x[0] == String.class- Parameters:
sig- a generic signature.- Since:
- 3.26
- See Also:
CtClass.setGenericSignature(String)
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createClass
public Class<?> createClass()
Generates a proxy class using the current filter. The module or package where a proxy class is created has to be opened to this package or the Javassist module.- See Also:
createClass(Lookup)
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createClass
public Class<?> createClass(MethodFilter filter)
Generates a proxy class using the supplied filter. The module or package where a proxy class is created has to be opened to this package or the Javassist module.
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createClass
public Class<?> createClass(MethodHandles.Lookup lookup)
Generates a proxy class using the current filter. It loads a class file by the givenjava.lang.invoke.MethodHandles.Lookupobject, which can be obtained byMethodHandles.lookup()called from somewhere in the package that the loaded class belongs to.- Parameters:
lookup- used for loading the proxy class. It needs an appropriate right to invokedefineClassfor the proxy class.- Since:
- 3.24
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createClass
public Class<?> createClass(MethodHandles.Lookup lookup, MethodFilter filter)
Generates a proxy class using the supplied filter.- Parameters:
lookup- used for loading the proxy class. It needs an appropriate right to invokedefineClassfor the proxy class.filter- the filter.- Since:
- 3.24
- See Also:
createClass(Lookup)
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getKey
public String getKey(Class<?> superClass, Class<?>[] interfaces, byte[] signature, boolean useWriteReplace)
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getHandler
public static MethodHandler getHandler(Proxy p)
Obtains the method handler of the given proxy object.- Parameters:
p- a proxy object.- Returns:
- the method handler.
- Since:
- 3.16
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create
public Object create(Class<?>[] paramTypes, Object[] args, MethodHandler mh) throws NoSuchMethodException, IllegalArgumentException, InstantiationException, IllegalAccessException, InvocationTargetException
Creates a proxy class and returns an instance of that class.- Parameters:
paramTypes- parameter types for a constructor.args- arguments passed to a constructor.mh- the method handler for the proxy class.- Throws:
NoSuchMethodExceptionIllegalArgumentExceptionInstantiationExceptionIllegalAccessExceptionInvocationTargetException- Since:
- 3.4
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create
public Object create(Class<?>[] paramTypes, Object[] args) throws NoSuchMethodException, IllegalArgumentException, InstantiationException, IllegalAccessException, InvocationTargetException
Creates a proxy class and returns an instance of that class.- Parameters:
paramTypes- parameter types for a constructor.args- arguments passed to a constructor.- Throws:
NoSuchMethodExceptionIllegalArgumentExceptionInstantiationExceptionIllegalAccessExceptionInvocationTargetException
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setHandler
@Deprecated public void setHandler(MethodHandler mi)
Deprecated.since 3.12 use of this method is incompatible with proxy class caching. instead clients should call methodProxy.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.Sets the default invocation handler. This invocation handler is shared among all the instances of a proxy class unless another is explicitly specified.
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