org.springframework.asm

Class ClassWriter

java.lang.Object

org.springframework.asm.ClassVisitor

org.springframework.asm.ClassWriter

public class ClassWriter
extends org.springframework.asm.ClassVisitor

A ClassVisitor that generates classes in bytecode form. More precisely this visitor generates a byte array conforming to the Java class file format. It can be used alone, to generate a Java class "from scratch", or with one or more ClassReader and adapter class visitor to generate a modified class from one or more existing Java classes.

Author:

Eric Bruneton

Field Summary

Fields

Modifier and Type	Field and Description
static int	COMPUTE_FRAMES Flag to automatically compute the stack map frames of methods from scratch.
static int	COMPUTE_MAXS Flag to automatically compute the maximum stack size and the maximum number of local variables of methods.

Fields inherited from class org.springframework.asm.ClassVisitor

api, cv

Constructor Summary

Constructors

Constructor and Description
ClassWriter(org.springframework.asm.ClassReader classReader, int flags) Constructs a new ClassWriter object and enables optimizations for "mostly add" bytecode transformations.
ClassWriter(int flags) Constructs a new ClassWriter object.

Method Summary

Methods

Modifier and Type	Method and Description
protected ClassLoader	getClassLoader()
protected String	getCommonSuperClass(String type1, String type2) Returns the common super type of the two given types.
int	newClass(String value) Adds a class reference to the constant pool of the class being build.
int	newConst(Object cst) Adds a number or string constant to the constant pool of the class being build.
int	newField(String owner, String name, String desc) Adds a field reference to the constant pool of the class being build.
int	newHandle(int tag, String owner, String name, String desc) Adds a handle to the constant pool of the class being build.
int	newInvokeDynamic(String name, String desc, org.springframework.asm.Handle bsm, Object... bsmArgs) Adds an invokedynamic reference to the constant pool of the class being build.
int	newMethod(String owner, String name, String desc, boolean itf) Adds a method reference to the constant pool of the class being build.
int	newMethodType(String methodDesc) Adds a method type reference to the constant pool of the class being build.
int	newNameType(String name, String desc) Adds a name and type to the constant pool of the class being build.
int	newUTF8(String value) Adds an UTF8 string to the constant pool of the class being build.
byte[]	toByteArray() Returns the bytecode of the class that was build with this class writer.
void	visit(int version, int access, String name, String signature, String superName, String[] interfaces)
org.springframework.asm.AnnotationVisitor	visitAnnotation(String desc, boolean visible)
void	visitAttribute(org.springframework.asm.Attribute attr)
void	visitEnd()
org.springframework.asm.FieldVisitor	visitField(int access, String name, String desc, String signature, Object value)
void	visitInnerClass(String name, String outerName, String innerName, int access)
org.springframework.asm.MethodVisitor	visitMethod(int access, String name, String desc, String signature, String[] exceptions)
void	visitOuterClass(String owner, String name, String desc)
void	visitSource(String file, String debug)
org.springframework.asm.AnnotationVisitor	visitTypeAnnotation(int typeRef, org.springframework.asm.TypePath typePath, String desc, boolean visible)

Methods inherited from class java.lang.Object

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

Field Detail

COMPUTE_MAXS

public static final int COMPUTE_MAXS

Flag to automatically compute the maximum stack size and the maximum number of local variables of methods. If this flag is set, then the arguments of the visitMaxs method of the MethodVisitor returned by the visitMethod method will be ignored, and computed automatically from the signature and the bytecode of each method.

See Also:

ClassWriter(int), Constant Field Values

COMPUTE_FRAMES

public static final int COMPUTE_FRAMES

Flag to automatically compute the stack map frames of methods from scratch. If this flag is set, then the calls to the MethodVisitor.visitFrame(int, int, java.lang.Object[], int, java.lang.Object[]) method are ignored, and the stack map frames are recomputed from the methods bytecode. The arguments of the visitMaxs method are also ignored and recomputed from the bytecode. In other words, computeFrames implies computeMaxs.

See Also:

ClassWriter(int), Constant Field Values

Constructor Detail

ClassWriter

public ClassWriter(int flags)

Constructs a new ClassWriter object.

Parameters:

flags - option flags that can be used to modify the default behavior of this class. See COMPUTE_MAXS, COMPUTE_FRAMES.

ClassWriter

public ClassWriter(org.springframework.asm.ClassReader classReader,
           int flags)

Constructs a new ClassWriter object and enables optimizations for "mostly add" bytecode transformations. These optimizations are the following:

• The constant pool from the original class is copied as is in the new class, which saves time. New constant pool entries will be added at the end if necessary, but unused constant pool entries won't be removed.
• Methods that are not transformed are copied as is in the new class, directly from the original class bytecode (i.e. without emitting visit events for all the method instructions), which saves a lot of time. Untransformed methods are detected by the fact that the ClassReader receives MethodVisitor objects that come from a ClassWriter (and not from any other ClassVisitor instance).

Parameters:

classReader - the ClassReader used to read the original class. It will be used to copy the entire constant pool from the original class and also to copy other fragments of original bytecode where applicable.

flags - option flags that can be used to modify the default behavior of this class. These option flags do not affect methods that are copied as is in the new class. This means that the maximum stack size nor the stack frames will be computed for these methods. See COMPUTE_MAXS, COMPUTE_FRAMES.

Method Detail

visit

public final void visit(int version,
         int access,
         String name,
         String signature,
         String superName,
         String[] interfaces)

Overrides:

visit in class org.springframework.asm.ClassVisitor

visitSource

public final void visitSource(String file,
               String debug)

Overrides:

visitSource in class org.springframework.asm.ClassVisitor

visitOuterClass

public final void visitOuterClass(String owner,
                   String name,
                   String desc)

Overrides:

visitOuterClass in class org.springframework.asm.ClassVisitor

visitAnnotation

public final org.springframework.asm.AnnotationVisitor visitAnnotation(String desc,
                                                        boolean visible)

Overrides:

visitAnnotation in class org.springframework.asm.ClassVisitor

visitTypeAnnotation

public final org.springframework.asm.AnnotationVisitor visitTypeAnnotation(int typeRef,
                                                            org.springframework.asm.TypePath typePath,
                                                            String desc,
                                                            boolean visible)

Overrides:

visitTypeAnnotation in class org.springframework.asm.ClassVisitor

visitAttribute

public final void visitAttribute(org.springframework.asm.Attribute attr)

Overrides:

visitAttribute in class org.springframework.asm.ClassVisitor

visitInnerClass

public final void visitInnerClass(String name,
                   String outerName,
                   String innerName,
                   int access)

Overrides:

visitInnerClass in class org.springframework.asm.ClassVisitor

visitField

public final org.springframework.asm.FieldVisitor visitField(int access,
                                              String name,
                                              String desc,
                                              String signature,
                                              Object value)

Overrides:

visitField in class org.springframework.asm.ClassVisitor

visitMethod

public final org.springframework.asm.MethodVisitor visitMethod(int access,
                                                String name,
                                                String desc,
                                                String signature,
                                                String[] exceptions)

Overrides:

visitMethod in class org.springframework.asm.ClassVisitor

visitEnd

public final void visitEnd()

Overrides:

visitEnd in class org.springframework.asm.ClassVisitor

toByteArray

public byte[] toByteArray()

Returns the bytecode of the class that was build with this class writer.

Returns:

the bytecode of the class that was build with this class writer.

newConst

public int newConst(Object cst)

Adds a number or string constant to the constant pool of the class being build. Does nothing if the constant pool already contains a similar item. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

cst - the value of the constant to be added to the constant pool. This parameter must be an Integer, a Float, a Long, a Double or a String.

Returns:

the index of a new or already existing constant item with the given value.

newUTF8

public int newUTF8(String value)

Adds an UTF8 string to the constant pool of the class being build. Does nothing if the constant pool already contains a similar item. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

value - the String value.

Returns:

the index of a new or already existing UTF8 item.

newClass

public int newClass(String value)

Adds a class reference to the constant pool of the class being build. Does nothing if the constant pool already contains a similar item. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

value - the internal name of the class.

Returns:

the index of a new or already existing class reference item.

newMethodType

public int newMethodType(String methodDesc)

Adds a method type reference to the constant pool of the class being build. Does nothing if the constant pool already contains a similar item. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

methodDesc - method descriptor of the method type.

Returns:

the index of a new or already existing method type reference item.

newHandle

public int newHandle(int tag,
            String owner,
            String name,
            String desc)

Adds a handle to the constant pool of the class being build. Does nothing if the constant pool already contains a similar item. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

tag - the kind of this handle. Must be Opcodes.H_GETFIELD, Opcodes.H_GETSTATIC, Opcodes.H_PUTFIELD, Opcodes.H_PUTSTATIC, Opcodes.H_INVOKEVIRTUAL, Opcodes.H_INVOKESTATIC, Opcodes.H_INVOKESPECIAL, Opcodes.H_NEWINVOKESPECIAL or Opcodes.H_INVOKEINTERFACE.

owner - the internal name of the field or method owner class.

name - the name of the field or method.

desc - the descriptor of the field or method.

Returns:

the index of a new or already existing method type reference item.

newInvokeDynamic

public int newInvokeDynamic(String name,
                   String desc,
                   org.springframework.asm.Handle bsm,
                   Object... bsmArgs)

Adds an invokedynamic reference to the constant pool of the class being build. Does nothing if the constant pool already contains a similar item. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

name - name of the invoked method.

desc - descriptor of the invoke method.

bsm - the bootstrap method.

bsmArgs - the bootstrap method constant arguments.

Returns:

the index of a new or already existing invokedynamic reference item.

newField

public int newField(String owner,
           String name,
           String desc)

Adds a field reference to the constant pool of the class being build. Does nothing if the constant pool already contains a similar item. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

owner - the internal name of the field's owner class.

name - the field's name.

desc - the field's descriptor.

Returns:

the index of a new or already existing field reference item.

newMethod

public int newMethod(String owner,
            String name,
            String desc,
            boolean itf)

Adds a method reference to the constant pool of the class being build. Does nothing if the constant pool already contains a similar item. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

owner - the internal name of the method's owner class.

name - the method's name.

desc - the method's descriptor.

itf - true if owner is an interface.

Returns:

the index of a new or already existing method reference item.

newNameType

public int newNameType(String name,
              String desc)

Adds a name and type to the constant pool of the class being build. Does nothing if the constant pool already contains a similar item. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

name - a name.

desc - a type descriptor.

Returns:

the index of a new or already existing name and type item.

getCommonSuperClass

protected String getCommonSuperClass(String type1,
                         String type2)

Returns the common super type of the two given types. The default implementation of this method loads the two given classes and uses the java.lang.Class methods to find the common super class. It can be overridden to compute this common super type in other ways, in particular without actually loading any class, or to take into account the class that is currently being generated by this ClassWriter, which can of course not be loaded since it is under construction.

Parameters:

type1 - the internal name of a class.

type2 - the internal name of another class.

Returns:

the internal name of the common super class of the two given classes.

getClassLoader

protected ClassLoader getClassLoader()