Package org.objectweb.asm

Class ClassWriter

java.lang.Object
org.objectweb.asm.ClassVisitor
org.objectweb.asm.ClassWriter
public class ClassWriter extends ClassVisitor
A ClassVisitor that generates a corresponding ClassFile structure, as defined in the Java Virtual Machine Specification (JVMS). It can be used alone, to generate a Java class "from scratch", or with one or more ClassReader and adapter ClassVisitor to generate a modified class from one or more existing Java classes.
See Also:

  • Field Details

  • Constructor Details

    • 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. Must be zero or more of COMPUTE_MAXS and COMPUTE_FRAMES.

    • ClassWriter

      public ClassWriter(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 and bootstrap methods from the original class are copied as is in the new class, which saves time. New constant pool entries and new bootstrap methods will be added at the end if necessary, but unused constant pool entries or bootstrap methods 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 and bootstrap methods 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. Must be zero or more of COMPUTE_MAXS and COMPUTE_FRAMES. These option flags do not affect methods that are copied as is in the new class. This means that neither the maximum stack size nor the stack frames will be computed for these methods.

  • Method Details

    • hasFlags

      public boolean hasFlags(int flags)
      Returns true if all the given flags were passed to the constructor.
      Parameters:
      flags - some option flags. Must be zero or more of COMPUTE_MAXS and COMPUTE_FRAMES.
      Returns:
      true if all the given flags, or more, were passed to the constructor.

    • visit

      public final void visit(int version, int access, String name, String signature, String superName, String[] interfaces)
      Description copied from class: ClassVisitor
      Visits the header of the class.
      Overrides:
      visit in class ClassVisitor
      Parameters:
      version - the class version. The minor version is stored in the 16 most significant bits, and the major version in the 16 least significant bits.
      access - the class's access flags (see Opcodes). This parameter also indicates if the class is deprecated Opcodes.ACC_DEPRECATED or a record Opcodes.ACC_RECORD.
      name - the internal name of the class (see Type.getInternalName()).
      signature - the signature of this class. May be null if the class is not a generic one, and does not extend or implement generic classes or interfaces.
      superName - the internal of name of the super class (see Type.getInternalName()). For interfaces, the super class is Object. May be null, but only for the Object class.
      interfaces - the internal names of the class's interfaces (see Type.getInternalName()). May be null.

    • visitSource

      public final void visitSource(String file, String debug)
      Description copied from class: ClassVisitor
      Visits the source of the class.
      Overrides:
      visitSource in class ClassVisitor
      Parameters:
      file - the name of the source file from which the class was compiled. May be null.
      debug - additional debug information to compute the correspondence between source and compiled elements of the class. May be null.

    • visitModule

      public final ModuleVisitor visitModule(String name, int access, String version)
      Description copied from class: ClassVisitor
      Visit the module corresponding to the class.
      Overrides:
      visitModule in class ClassVisitor
      Parameters:
      name - the fully qualified name (using dots) of the module.
      access - the module access flags, among ACC_OPEN, ACC_SYNTHETIC and ACC_MANDATED.
      version - the module version, or null.
      Returns:
      a visitor to visit the module values, or null if this visitor is not interested in visiting this module.

    • visitNestHost

      public final void visitNestHost(String nestHost)
      Description copied from class: ClassVisitor
      Visits the nest host class of the class. A nest is a set of classes of the same package that share access to their private members. One of these classes, called the host, lists the other members of the nest, which in turn should link to the host of their nest. This method must be called only once and only if the visited class is a non-host member of a nest. A class is implicitly its own nest, so it's invalid to call this method with the visited class name as argument.
      Overrides:
      visitNestHost in class ClassVisitor
      Parameters:
      nestHost - the internal name of the host class of the nest (see Type.getInternalName()).

    • visitOuterClass

      public final void visitOuterClass(String owner, String name, String descriptor)
      Description copied from class: ClassVisitor
      Visits the enclosing class of the class. This method must be called only if this class is a local or anonymous class. See the JVMS 4.7.7 section for more details.
      Overrides:
      visitOuterClass in class ClassVisitor
      Parameters:
      owner - internal name of the enclosing class of the class (see Type.getInternalName()).
      name - the name of the method that contains the class, or null if the class is not enclosed in a method or constructor of its enclosing class (e.g. if it is enclosed in an instance initializer, static initializer, instance variable initializer, or class variable initializer).
      descriptor - the descriptor of the method that contains the class, or null if the class is not enclosed in a method or constructor of its enclosing class (e.g. if it is enclosed in an instance initializer, static initializer, instance variable initializer, or class variable initializer).

    • visitAnnotation

      public final AnnotationVisitor visitAnnotation(String descriptor, boolean visible)
      Description copied from class: ClassVisitor
      Visits an annotation of the class.
      Overrides:
      visitAnnotation in class ClassVisitor
      Parameters:
      descriptor - the class descriptor of the annotation class.
      visible - true if the annotation is visible at runtime.
      Returns:
      a visitor to visit the annotation values, or null if this visitor is not interested in visiting this annotation.

    • visitTypeAnnotation

      public final AnnotationVisitor visitTypeAnnotation(int typeRef, TypePath typePath, String descriptor, boolean visible)
      Description copied from class: ClassVisitor
      Visits an annotation on a type in the class signature.
      Overrides:
      visitTypeAnnotation in class ClassVisitor
      Parameters:
      typeRef - a reference to the annotated type. The sort of this type reference must be TypeReference.CLASS_TYPE_PARAMETER, TypeReference.CLASS_TYPE_PARAMETER_BOUND or TypeReference.CLASS_EXTENDS. See TypeReference.
      typePath - the path to the annotated type argument, wildcard bound, array element type, or static inner type within 'typeRef'. May be null if the annotation targets 'typeRef' as a whole.
      descriptor - the class descriptor of the annotation class.
      visible - true if the annotation is visible at runtime.
      Returns:
      a visitor to visit the annotation values, or null if this visitor is not interested in visiting this annotation.

    • visitAttribute

      public final void visitAttribute(Attribute attribute)
      Description copied from class: ClassVisitor
      Visits a non standard attribute of the class.
      Overrides:
      visitAttribute in class ClassVisitor
      Parameters:
      attribute - an attribute.

    • visitNestMember

      public final void visitNestMember(String nestMember)
      Description copied from class: ClassVisitor
      Visits a member of the nest. A nest is a set of classes of the same package that share access to their private members. One of these classes, called the host, lists the other members of the nest, which in turn should link to the host of their nest. This method must be called only if the visited class is the host of a nest. A nest host is implicitly a member of its own nest, so it's invalid to call this method with the visited class name as argument.
      Overrides:
      visitNestMember in class ClassVisitor
      Parameters:
      nestMember - the internal name of a nest member (see Type.getInternalName()).

    • visitPermittedSubclass

      public final void visitPermittedSubclass(String permittedSubclass)
      Description copied from class: ClassVisitor
      Visits a permitted subclasses. A permitted subclass is one of the allowed subclasses of the current class.
      Overrides:
      visitPermittedSubclass in class ClassVisitor
      Parameters:
      permittedSubclass - the internal name of a permitted subclass (see Type.getInternalName()).

    • visitInnerClass

      public final void visitInnerClass(String name, String outerName, String innerName, int access)
      Description copied from class: ClassVisitor
      Visits information about an inner class. This inner class is not necessarily a member of the class being visited. More precisely, every class or interface C which is referenced by this class and which is not a package member must be visited with this method. This class must reference its nested class or interface members, and its enclosing class, if any. See the JVMS 4.7.6 section for more details.
      Overrides:
      visitInnerClass in class ClassVisitor
      Parameters:
      name - the internal name of C (see Type.getInternalName()).
      outerName - the internal name of the class or interface C is a member of (see Type.getInternalName()). Must be null if C is not the member of a class or interface (e.g. for local or anonymous classes).
      innerName - the (simple) name of C. Must be null for anonymous inner classes.
      access - the access flags of C originally declared in the source code from which this class was compiled.

    • visitRecordComponent

      public final RecordComponentVisitor visitRecordComponent(String name, String descriptor, String signature)
      Description copied from class: ClassVisitor
      Visits a record component of the class.
      Overrides:
      visitRecordComponent in class ClassVisitor
      Parameters:
      name - the record component name.
      descriptor - the record component descriptor (see Type).
      signature - the record component signature. May be null if the record component type does not use generic types.
      Returns:
      a visitor to visit this record component annotations and attributes, or null if this class visitor is not interested in visiting these annotations and attributes.

    • visitField

      public final FieldVisitor visitField(int access, String name, String descriptor, String signature, Object value)
      Description copied from class: ClassVisitor
      Visits a field of the class.
      Overrides:
      visitField in class ClassVisitor
      Parameters:
      access - the field's access flags (see Opcodes). This parameter also indicates if the field is synthetic and/or deprecated.
      name - the field's name.
      descriptor - the field's descriptor (see Type).
      signature - the field's signature. May be null if the field's type does not use generic types.
      value - the field's initial value. This parameter, which may be null if the field does not have an initial value, must be an Integer, a Float, a Long, a Double or a String (for int, float, long or String fields respectively). This parameter is only used for static fields. Its value is ignored for non static fields, which must be initialized through bytecode instructions in constructors or methods.
      Returns:
      a visitor to visit field annotations and attributes, or null if this class visitor is not interested in visiting these annotations and attributes.

    • visitMethod

      public final MethodVisitor visitMethod(int access, String name, String descriptor, String signature, String[] exceptions)
      Description copied from class: ClassVisitor
      Visits a method of the class. This method must return a new MethodVisitor instance (or null) each time it is called, i.e., it should not return a previously returned visitor.
      Overrides:
      visitMethod in class ClassVisitor
      Parameters:
      access - the method's access flags (see Opcodes). This parameter also indicates if the method is synthetic and/or deprecated.
      name - the method's name.
      descriptor - the method's descriptor (see Type).
      signature - the method's signature. May be null if the method parameters, return type and exceptions do not use generic types.
      exceptions - the internal names of the method's exception classes (see Type.getInternalName()). May be null.
      Returns:
      an object to visit the byte code of the method, or null if this class visitor is not interested in visiting the code of this method.

    • visitEnd

      public final void visitEnd()
      Description copied from class: ClassVisitor
      Visits the end of the class. This method, which is the last one to be called, is used to inform the visitor that all the fields and methods of the class have been visited.
      Overrides:
      visitEnd in class ClassVisitor

    • toByteArray

      public byte[] toByteArray()
      Returns the content of the class file that was built by this ClassWriter.
      Returns:
      the binary content of the JVMS ClassFile structure that was built by this ClassWriter.
      Throws:
      ClassTooLargeException - if the constant pool of the class is too large.
      MethodTooLargeException - if the Code attribute of a method is too large.

    • newConst

      public int newConst(Object value)
      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:
      value - 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 (see Type.getInternalName()).
      Returns:
      the index of a new or already existing class reference item.

    • newMethodType

      public int newMethodType(String methodDescriptor)
      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:
      methodDescriptor - method descriptor of the method type.
      Returns:
      the index of a new or already existing method type reference item.

    • newModule

      public int newModule(String moduleName)
      Adds a module 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:
      moduleName - name of the module.
      Returns:
      the index of a new or already existing module reference item.

    • newPackage

      public int newPackage(String packageName)
      Adds a package 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:
      packageName - name of the package in its internal form.
      Returns:
      the index of a new or already existing module reference item.

    • newHandle

      @Deprecated public int newHandle(int tag, String owner, String name, String descriptor)
      Deprecated.
      this method is superseded by newHandle(int, String, String, String, boolean).
      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 (see Type.getInternalName()).
      name - the name of the field or method.
      descriptor - the descriptor of the field or method.
      Returns:
      the index of a new or already existing method type reference item.

    • newHandle

      public int newHandle(int tag, String owner, String name, String descriptor, boolean isInterface)
      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 (see Type.getInternalName()).
      name - the name of the field or method.
      descriptor - the descriptor of the field or method.
      isInterface - true if the owner is an interface.
      Returns:
      the index of a new or already existing method type reference item.

    • newConstantDynamic

      public int newConstantDynamic(String name, String descriptor, Handle bootstrapMethodHandle, Object... bootstrapMethodArguments)
      Adds a dynamic constant 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.
      descriptor - field descriptor of the constant type.
      bootstrapMethodHandle - the bootstrap method.
      bootstrapMethodArguments - the bootstrap method constant arguments.
      Returns:
      the index of a new or already existing dynamic constant reference item.

    • newInvokeDynamic

      public int newInvokeDynamic(String name, String descriptor, Handle bootstrapMethodHandle, Object... bootstrapMethodArguments)
      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.
      descriptor - descriptor of the invoke method.
      bootstrapMethodHandle - the bootstrap method.
      bootstrapMethodArguments - 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 descriptor)
      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 (see Type.getInternalName()).
      name - the field's name.
      descriptor - 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 descriptor, boolean isInterface)
      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 (see Type.getInternalName()).
      name - the method's name.
      descriptor - the method's descriptor.
      isInterface - 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 descriptor)
      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.
      descriptor - a type descriptor.
      Returns:
      the index of a new or already existing name and type item.

    • setFlags

      public final void setFlags(int flags)
      Changes the computation strategy of method properties like max stack size, max number of local variables, and frames.

      WARNING: setFlags(int) method changes the behavior of new method visitors returned from visitMethod(int, String, String, String, String[]). The behavior will be changed only after the next method visitor is returned. All the previously returned method visitors keep their previous behavior.

      Parameters:
      flags - option flags that can be used to modify the default behavior of this class. Must be zero or more of COMPUTE_MAXS and COMPUTE_FRAMES.

    • 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 (see Type.getInternalName()).
      type2 - the internal name of another class (see Type.getInternalName()).
      Returns:
      the internal name of the common super class of the two given classes (see Type.getInternalName()).

    • getClassLoader

      protected ClassLoader getClassLoader()
      Returns the ClassLoader to be used by the default implementation of getCommonSuperClass(String, String), that of this ClassWriter's runtime type by default.
      Returns:
      ClassLoader