net.bytebuddy.asm

Class Advice

java.lang.Object

net.bytebuddy.asm.Advice

All Implemented Interfaces:

AsmVisitorWrapper.ForDeclaredMethods.MethodVisitorWrapper, InstrumentedType.Prepareable, Implementation

@HashCodeAndEqualsPlugin.Enhance
public class Advice
extends Object
implements AsmVisitorWrapper.ForDeclaredMethods.MethodVisitorWrapper, Implementation

Advice wrappers copy the code of blueprint methods to be executed before and/or after a matched method. To achieve this, a static method of a class is annotated by Advice.OnMethodEnter and/or Advice.OnMethodExit and provided to an instance of this class.

A method that is annotated with Advice.OnMethodEnter can annotate its parameters with Advice.Argument where field access to this parameter is substituted with access to the specified argument of the instrumented method. Alternatively, a parameter can be annotated by Advice.This where the this reference of the instrumented method is read when the parameter is accessed. This mechanism can also be used to assign a new value to the this reference of an instrumented method. If no annotation is used on a parameter, it is assigned the n-th parameter of the instrumented method for the n-th parameter of the advice method. All parameters must declare the exact same type as the parameters of the instrumented type or the method's declaring type for the Advice.This reference respectively if they are not marked as read-only. In the latter case, it suffices that a parameter type is a super type of the corresponding type of the instrumented method.

A method that is annotated with Advice.OnMethodExit can equally annotate its parameters with Advice.Argument and Advice.This. Additionally, it can annotate a parameter with Advice.Return to receive the original method's return value. By reassigning the return value, it is possible to replace the returned value. If an instrumented method does not return a value, this annotation must not be used. If a method returns exceptionally, the parameter is set to its default value, i.e. to 0 for primitive types and to null for reference types. The parameter's type must be equal to the instrumented method's return type if it is not set to read-only where it suffices to declare the parameter type to be of any super type to the instrumented method's return type. An exception can be read by annotating a parameter of type Throwable annotated with Advice.Thrown which is assigned the thrown Throwable or null if a method returns normally. Doing so, it is possible to exchange a thrown exception with any checked or unchecked exception.Finally, if a method annotated with Advice.OnMethodEnter exists and this method returns a value, this value can be accessed by a parameter annotated with Advice.Enter. This parameter must declare the same type as type being returned by the method annotated with Advice.OnMethodEnter. If the parameter is marked to be read-only, it suffices that the annotated parameter is of a super type of the return type of the method annotated by Advice.OnMethodEnter. If no such method exists or this method returns void, no such parameter must be declared. Any return value of a method that is annotated by Advice.OnMethodExit is discarded.

If any advice method throws an exception, the method is terminated prematurely. If the method annotated by Advice.OnMethodEnter throws an exception, the method annotated by Advice.OnMethodExit method is not invoked. If the instrumented method throws an exception, the method that is annotated by Advice.OnMethodExit is only invoked if the Advice.OnMethodExit.onThrowable() property is set to true what is the default. If this property is set to false, the Advice.Thrown annotation must not be used on any parameter.

Byte Buddy does not assert the visibility of any types that are referenced within an inlined advice method. It is the responsibility of the user of this class to assure that all types referenced within the advice methods are visible to the instrumented class. Failing to do so results in a IllegalAccessError at the instrumented class's runtime.

Advice can be used either as a AsmVisitorWrapper where any declared methods of the currently instrumented type are enhanced without replacing an existing implementation. Alternatively, advice can function as an Implementation where, by default, the original super or default method of the instrumented method is invoked. If this is not possible or undesired, the delegate implementation can be changed by specifying a wrapped implementation explicitly by wrap(Implementation).

When using an advice class as a visitor wrapper, native or abstract methods which are silently skipped when advice matches such a method.

Important: Since Java 6, class files contain stack map frames embedded into a method's byte code. When advice methods are compiled with a class file version less then Java 6 but are used for a class file that was compiled to Java 6 or newer, these stack map frames must be computed by ASM by using the ClassWriter.COMPUTE_FRAMES option. If the advice methods do not contain any branching instructions, this is not required. No action is required if the advice methods are at least compiled with Java 6 but are used on classes older than Java 6. This limitation only applies to advice methods that are inlined. Also, it is the responsibility of this class's user to assure that the advice method does not contain byte code constructs that are not supported by the class containing the instrumented method. In particular, pre Java-5 try-finally blocks cannot be inlined into classes with newer byte code levels as the jsr instruction was deprecated. Also, classes prior to Java 7 do not support the invokedynamic command which must not be contained by an advice method if the instrumented method targets an older class file format version.

Note: For the purpose of inlining, Java 5 and Java 6 byte code can be seen as the best candidate for advice methods. These versions do no longer allow subroutines, neither do they already allow invokedynamic instructions or method handles. This way, Java 5 and Java 6 byte code is compatible to both older and newer versions. One exception for backwards-incompatible byte code is the possibility to load type references from the constant pool onto the operand stack. These instructions can however easily be transformed for classes compiled to Java 4 and older by registering a TypeConstantAdjustment before the advice visitor.

Note: It is not possible to trigger break points in inlined advice methods as the debugging information of the inlined advice is not preserved. It is not possible in Java to reference more than one source file per class what makes translating such debugging information impossible. It is however possible to set break points in advice methods when invoking the original advice target. This allows debugging of advice code within unit tests that invoke the advice method without instrumentation. As a consequence of not transferring debugging information, the names of the parameters of an advice method do not matter when inlining, neither does any meta information on the advice method's body such as annotations or parameter modifiers.

Note: The behavior of this component is undefined if it is supplied with invalid byte code what might result in runtime exceptions.

Note: When using advice from a Java agent with an AgentBuilder, it often makes sense to not include any library-specific code in the agent's jar file. For being able to locate the advice code in the context of the library dependencies, Byte Buddy offers an AgentBuilder.Transformer.ForAdvice implementation that allows registering the agent's class file locators for assembly of the advice class's description at runtime and with respect to the specific user dependencies.

See Also:

Advice.OnMethodEnter, Advice.OnMethodExit

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
protected static class	Advice.AdviceVisitor A method visitor that weaves the advice methods' byte codes.
static interface	Advice.AllArguments Assigns an array containing all arguments of the instrumented method to the annotated parameter.
protected static class	Advice.Appender A byte code appender for implementing Advice.
static interface	Advice.Argument Indicates that the annotated parameter should be mapped to the parameter with index Advice.Argument.value() of the instrumented method.
static interface	Advice.ArgumentHandler An argument handler is responsible for resolving offsets of the local variable array in the context of the applied instrumentation.
static class	Advice.AssignReturned A post processor that uses the return value of an advice method to define values for fields, arguments, the instrumented method's return value or the exception being thrown.
protected static interface	Advice.Delegator Materializes an advice invocation within a delegation.
protected static interface	Advice.Dispatcher A dispatcher for implementing advice.
static interface	Advice.Enter Indicates that the annotated parameter should be mapped to the value that is returned by the advice method that is annotated by Advice.OnMethodEnter.
static interface	Advice.ExceptionHandler An exception handler is responsible for providing byte code for handling an exception thrown from a suppressing advice method.
static interface	Advice.Exit Indicates that the annotated parameter should be mapped to the value that is returned by the advice method that is annotated by Advice.OnMethodExit.
static interface	Advice.FieldValue Indicates that the annotated parameter should be mapped to a field in the scope of the instrumented method.
static interface	Advice.Local Declares the annotated parameter as a local variable that is created by Byte Buddy for the instrumented method.
protected static interface	Advice.MethodSizeHandler A handler for computing the instrumented method's size.
static interface	Advice.OffsetMapping Represents an offset mapping for an advice method to an alternative offset.
static class	Advice.OnDefaultValue A marker type to be used as an argument for Advice.OnMethodEnter.skipOn().
static interface	Advice.OnMethodEnter Indicates that this method should be inlined before the matched method is invoked.
static interface	Advice.OnMethodExit Indicates that this method should be executed before exiting the instrumented method.
static class	Advice.OnNonDefaultValue A marker type to be used as an argument for Advice.OnMethodEnter.skipOn().
static interface	Advice.Origin Indicates that the annotated parameter should be mapped to a string representation of the instrumented method, a constant representing the Class declaring the adviced method or a Method, Constructor or java.lang.reflect.Executable representing this method.
static interface	Advice.PostProcessor A post processor for advice methods that is invoked after advice is executed.
static interface	Advice.Return Indicates that the annotated parameter should be mapped to the return value of the instrumented method.
static interface	Advice.StackMapFrameHandler A handler for computing and translating stack map frames.
static interface	Advice.StubValue Indicates that the annotated parameter should always return a default a boxed version of the instrumented methods return value (i.e.
static interface	Advice.This Indicates that the annotated parameter should be mapped to the this reference of the instrumented method.
static interface	Advice.Thrown Indicates that the annotated parameter should be mapped to the Throwable thrown by the instrumented method or to null if the method returned regularly.
static interface	Advice.Unused Indicates that the annotated parameter should always return a default value (i.e.
static class	Advice.WithCustomMapping A builder step for creating an Advice that uses custom mappings of annotations to constant pool values.

Nested classes/interfaces inherited from interface net.bytebuddy.implementation.Implementation

Implementation.Composable, Implementation.Compound, Implementation.Context, Implementation.Simple, Implementation.SpecialMethodInvocation, Implementation.Target

Nested classes/interfaces inherited from interface net.bytebuddy.dynamic.scaffold.InstrumentedType.Prepareable

InstrumentedType.Prepareable.NoOp

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	Advice(Advice.Dispatcher.Resolved.ForMethodEnter methodEnter, Advice.Dispatcher.Resolved.ForMethodExit methodExit) Creates a new advice.

Method Summary

Modifier and Type	Method and Description
ByteCodeAppender	appender(Implementation.Target implementationTarget) Creates a byte code appender that determines the implementation of the instrumented type's methods.
protected org.objectweb.asm.MethodVisitor	doWrap(TypeDescription instrumentedType, MethodDescription instrumentedMethod, org.objectweb.asm.MethodVisitor methodVisitor, Implementation.Context implementationContext, int writerFlags, int readerFlags) Wraps the method visitor to implement this advice.
AsmVisitorWrapper.ForDeclaredMethods	on(ElementMatcher<? super MethodDescription> matcher) Returns an ASM visitor wrapper that matches the given matcher and applies this advice to the matched methods.
InstrumentedType	prepare(InstrumentedType instrumentedType) Prepares a given instrumented type.
static Advice	to(Class<?> advice) Implements advice where every matched method is advised by the given type's advisory methods.
static Advice	to(Class<?> enterAdvice, Class<?> exitAdvice) Implements advice where every matched method is advised by the given type's advisory methods.
static Advice	to(Class<?> enterAdvice, Class<?> exitAdvice, ClassFileLocator classFileLocator) Implements advice where every matched method is advised by the given type's advisory methods.
static Advice	to(Class<?> advice, ClassFileLocator classFileLocator) Implements advice where every matched method is advised by the given type's advisory methods.
static Advice	to(TypeDescription advice) Implements advice where every matched method is advised by the given type's advisory methods.
protected static Advice	to(TypeDescription advice, Advice.PostProcessor.Factory postProcessorFactory, ClassFileLocator classFileLocator, List<? extends Advice.OffsetMapping.Factory<?>> userFactories, Advice.Delegator delegator) Creates a new advice.
static Advice	to(TypeDescription advice, ClassFileLocator classFileLocator) Implements advice where every matched method is advised by the given type's advisory methods.
static Advice	to(TypeDescription enterAdvice, TypeDescription exitAdvice) Implements advice where every matched method is advised by the given type's advisory methods.
protected static Advice	to(TypeDescription enterAdvice, TypeDescription exitAdvice, Advice.PostProcessor.Factory postProcessorFactory, ClassFileLocator classFileLocator, List<? extends Advice.OffsetMapping.Factory<?>> userFactories, Advice.Delegator delegator) Creates a new advice.
static Advice	to(TypeDescription enterAdvice, TypeDescription exitAdvice, ClassFileLocator classFileLocator) Implements advice where every matched method is advised by the given type's advisory methods.
Advice	withAssigner(Assigner assigner) Configures this advice to use the specified assigner.
static Advice.WithCustomMapping	withCustomMapping() Allows for the configuration of custom annotations that are then bound to a dynamically computed, constant value.
Advice	withExceptionHandler(Advice.ExceptionHandler exceptionHandler) Configures this advice to execute the given exception handler upon a suppressed exception.
Advice	withExceptionHandler(StackManipulation exceptionHandler) Configures this advice to execute the given stack manipulation upon a suppressed exception.
Advice	withExceptionPrinting() Configures this advice to call Throwable.printStackTrace() upon a suppressed exception.
Implementation	wrap(Implementation implementation) Wraps the supplied implementation to have this advice applied around it.
org.objectweb.asm.MethodVisitor	wrap(TypeDescription instrumentedType, MethodDescription instrumentedMethod, org.objectweb.asm.MethodVisitor methodVisitor, Implementation.Context implementationContext, TypePool typePool, int writerFlags, int readerFlags) Wraps a method visitor.

Methods inherited from class java.lang.Object

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

Constructor Detail

Advice

protected Advice(Advice.Dispatcher.Resolved.ForMethodEnter methodEnter,
                 Advice.Dispatcher.Resolved.ForMethodExit methodExit)

Creates a new advice.

Parameters:

methodEnter - The dispatcher for instrumenting the instrumented method upon entering.

methodExit - The dispatcher for instrumenting the instrumented method upon exiting.

Method Detail

to

public static Advice to(Class<?> advice)

Implements advice where every matched method is advised by the given type's advisory methods. The advices binary representation is accessed by querying the class loader of the supplied class for a class file.

Parameters:

advice - The type declaring the advice.

Returns:

A method visitor wrapper representing the supplied advice.

to

public static Advice to(Class<?> advice,
                        ClassFileLocator classFileLocator)

Implements advice where every matched method is advised by the given type's advisory methods.

Parameters:

advice - The type declaring the advice.

classFileLocator - The class file locator for locating the advisory class's class file.

Returns:

A method visitor wrapper representing the supplied advice.

to

public static Advice to(TypeDescription advice)

Implements advice where every matched method is advised by the given type's advisory methods. Using this method, a non-operational class file locator is specified for the advice target. This implies that only advice targets with the inline target set to false are resolvable by the returned instance.

Parameters:

advice - The type declaring the advice.

Returns:

A method visitor wrapper representing the supplied advice.

to

public static Advice to(TypeDescription advice,
                        ClassFileLocator classFileLocator)

Implements advice where every matched method is advised by the given type's advisory methods.

Parameters:

advice - A description of the type declaring the advice.

classFileLocator - The class file locator for locating the advisory class's class file.

Returns:

A method visitor wrapper representing the supplied advice.

to

protected static Advice to(TypeDescription advice,
                           Advice.PostProcessor.Factory postProcessorFactory,
                           ClassFileLocator classFileLocator,
                           List<? extends Advice.OffsetMapping.Factory<?>> userFactories,
                           Advice.Delegator delegator)

Creates a new advice.

Parameters:

advice - A description of the type declaring the advice.

postProcessorFactory - The post processor factory to use.

classFileLocator - The class file locator for locating the advisory class's class file.

userFactories - A list of custom factories for user generated offset mappings.

delegator - The delegator to use.

Returns:

A method visitor wrapper representing the supplied advice.

to

public static Advice to(Class<?> enterAdvice,
                        Class<?> exitAdvice)

Implements advice where every matched method is advised by the given type's advisory methods. The advices binary representation is accessed by querying the class loader of the supplied class for a class file.

Parameters:

enterAdvice - The type declaring the enter advice.

exitAdvice - The type declaring the exit advice.

Returns:

A method visitor wrapper representing the supplied advice.

to

public static Advice to(Class<?> enterAdvice,
                        Class<?> exitAdvice,
                        ClassFileLocator classFileLocator)

Implements advice where every matched method is advised by the given type's advisory methods.

Parameters:

enterAdvice - The type declaring the enter advice.

exitAdvice - The type declaring the exit advice.

classFileLocator - The class file locator for locating the advisory class's class file.

Returns:

A method visitor wrapper representing the supplied advice.

to

public static Advice to(TypeDescription enterAdvice,
                        TypeDescription exitAdvice)

Implements advice where every matched method is advised by the given type's advisory methods. Using this method, a non-operational class file locator is specified for the advice target. This implies that only advice targets with the inline target set to false are resolvable by the returned instance.

Parameters:

enterAdvice - The type declaring the enter advice.

exitAdvice - The type declaring the exit advice.

Returns:

A method visitor wrapper representing the supplied advice.

to

public static Advice to(TypeDescription enterAdvice,
                        TypeDescription exitAdvice,
                        ClassFileLocator classFileLocator)

Implements advice where every matched method is advised by the given type's advisory methods.

Parameters:

enterAdvice - The type declaring the enter advice.

exitAdvice - The type declaring the exit advice.

classFileLocator - The class file locator for locating the advisory class's class file.

Returns:

A method visitor wrapper representing the supplied advice.

to

protected static Advice to(TypeDescription enterAdvice,
                           TypeDescription exitAdvice,
                           Advice.PostProcessor.Factory postProcessorFactory,
                           ClassFileLocator classFileLocator,
                           List<? extends Advice.OffsetMapping.Factory<?>> userFactories,
                           Advice.Delegator delegator)

Creates a new advice.

Parameters:

enterAdvice - The type declaring the enter advice.

exitAdvice - The type declaring the exit advice.

postProcessorFactory - The post processor factory to use.

classFileLocator - The class file locator for locating the advisory class's class file.

userFactories - A list of custom factories for user generated offset mappings.

delegator - The delegator to use.

Returns:

A method visitor wrapper representing the supplied advice.

withCustomMapping

public static Advice.WithCustomMapping withCustomMapping()

Allows for the configuration of custom annotations that are then bound to a dynamically computed, constant value.

Returns:

A builder for an Advice instrumentation with custom values.

See Also:

Advice.OffsetMapping.Factory

on

public AsmVisitorWrapper.ForDeclaredMethods on(ElementMatcher<? super MethodDescription> matcher)

Returns an ASM visitor wrapper that matches the given matcher and applies this advice to the matched methods.

Parameters:

matcher - The matcher identifying methods to apply the advice to.

Returns:

A suitable ASM visitor wrapper with the compute frames option enabled.

wrap

public org.objectweb.asm.MethodVisitor wrap(TypeDescription instrumentedType,
                                            MethodDescription instrumentedMethod,
                                            org.objectweb.asm.MethodVisitor methodVisitor,
                                            Implementation.Context implementationContext,
                                            TypePool typePool,
                                            int writerFlags,
                                            int readerFlags)

Wraps a method visitor.

Specified by:

wrap in interface AsmVisitorWrapper.ForDeclaredMethods.MethodVisitorWrapper

Parameters:

instrumentedType - The instrumented type.

instrumentedMethod - The method that is currently being defined.

methodVisitor - The original field visitor that defines the given method.

implementationContext - The implementation context to use.

typePool - The type pool to use.

writerFlags - The ASM ClassWriter reader flags to consider.

readerFlags - The ASM ClassReader reader flags to consider.

Returns:

The wrapped method visitor.

doWrap

protected org.objectweb.asm.MethodVisitor doWrap(TypeDescription instrumentedType,
                                                 MethodDescription instrumentedMethod,
                                                 org.objectweb.asm.MethodVisitor methodVisitor,
                                                 Implementation.Context implementationContext,
                                                 int writerFlags,
                                                 int readerFlags)

Wraps the method visitor to implement this advice.

Parameters:

instrumentedType - The instrumented type.

instrumentedMethod - The instrumented method.

methodVisitor - The method visitor to write to.

implementationContext - The implementation context to use.

writerFlags - The ASM writer flags to use.

readerFlags - The ASM reader flags to use.

Returns:

A method visitor that applies this advice.

prepare

public InstrumentedType prepare(InstrumentedType instrumentedType)

Prepares a given instrumented type.

Specified by:

prepare in interface InstrumentedType.Prepareable

Parameters:

instrumentedType - The instrumented type in its current form.

Returns:

The prepared instrumented type.

appender

public ByteCodeAppender appender(Implementation.Target implementationTarget)

Creates a byte code appender that determines the implementation of the instrumented type's methods.

Specified by:

appender in interface Implementation

Parameters:

implementationTarget - The target of the current implementation.

Returns:

A byte code appender for implementing methods delegated to this implementation. This byte code appender is also responsible for handling methods that were added by this implementation on the call to InstrumentedType.Prepareable.prepare(InstrumentedType).

withAssigner

public Advice withAssigner(Assigner assigner)

Configures this advice to use the specified assigner. Any previous or default assigner is replaced.

Parameters:

assigner - The assigner to use,

Returns:

A version of this advice that uses the specified assigner.

withExceptionPrinting

public Advice withExceptionPrinting()

Configures this advice to call Throwable.printStackTrace() upon a suppressed exception.

Returns:

A version of this advice that prints any suppressed exception.

withExceptionHandler

public Advice withExceptionHandler(StackManipulation exceptionHandler)

Configures this advice to execute the given stack manipulation upon a suppressed exception. The stack manipulation is executed with a Throwable instance on the operand stack. The stack must be empty upon completing the exception handler.

Parameters:

exceptionHandler - The exception handler to apply.

Returns:

A version of this advice that applies the supplied exception handler.

withExceptionHandler

public Advice withExceptionHandler(Advice.ExceptionHandler exceptionHandler)

Configures this advice to execute the given exception handler upon a suppressed exception. The stack manipulation is executed with a Throwable instance on the operand stack. The stack must be empty upon completing the exception handler.

Parameters:

exceptionHandler - The exception handler to apply.

Returns:

A version of this advice that applies the supplied exception handler.

wrap

public Implementation wrap(Implementation implementation)

Wraps the supplied implementation to have this advice applied around it.

Parameters:

implementation - The implementation to wrap.

Returns:

An implementation that applies the supplied implementation and wraps it with this advice.