Package org.objectweb.asm.util

Class CheckClassAdapter

java.lang.Object
org.objectweb.asm.ClassVisitor
org.objectweb.asm.util.CheckClassAdapter
public class CheckClassAdapter extends ClassVisitor
A ClassVisitor that checks that its methods are properly used. More precisely this class adapter checks each method call individually, based only on its arguments, but does not check the sequence of method calls. For example, the invalid sequence visitField(ACC_PUBLIC, "i", "I", null) visitField(ACC_PUBLIC, "i", "D", null) will not be detected by this class adapter.

CheckClassAdapter can be also used to verify bytecode transformations in order to make sure that the transformed bytecode is sane. For example: 

 InputStream inputStream = ...; // get bytes for the source class
 ClassReader classReader = new ClassReader(inputStream);
 ClassWriter classWriter = new ClassWriter(classReader, ClassWriter.COMPUTE_MAXS);
 ClassVisitor classVisitor = new MyClassAdapter(new CheckClassAdapter(classWriter, true));
 classReader.accept(classVisitor, 0);

 StringWriter stringWriter = new StringWriter();
 PrintWriter printWriter = new PrintWriter(stringWriter);
 CheckClassAdapter.verify(new ClassReader(classWriter.toByteArray()), false, printWriter);
 assertTrue(stringWriter.toString().isEmpty());

The above code pass the transformed bytecode through a CheckClassAdapter, with data flow checks enabled. These checks are not exactly the same as the JVM verification, but provide some basic type checking for each method instruction. If the bytecode has errors, the output text shows the erroneous instruction number, and a dump of the failed method with information about the type of the local variables and of the operand stack slots for each instruction. For example (format is - insnNumber locals : stack): 

 org.objectweb.asm.tree.analysis.AnalyzerException: Error at instruction 71: Expected I, but found .
   at org.objectweb.asm.tree.analysis.Analyzer.analyze(Analyzer.java:...)
   at org.objectweb.asm.util.CheckClassAdapter.verify(CheckClassAdapter.java:...)
 ...
 remove()V
 00000 LinkedBlockingQueue$Itr . . . . . . . .  : ICONST_0
 00001 LinkedBlockingQueue$Itr . . . . . . . .  : I ISTORE 2
 00001 LinkedBlockingQueue$Itr . I . . . . . .  :
 ...
 00071 LinkedBlockingQueue$Itr . I . . . . . .  : ILOAD 1
 00072 ? INVOKESPECIAL java/lang/Integer.<init> (I)V
 ...

The above output shows that the local variable 1, loaded by the ILOAD 1 instruction at position 00071 is not initialized, whereas the local variable 2 is initialized and contains an int value.

  • Constructor Details

    • CheckClassAdapter

      public CheckClassAdapter(ClassVisitor classVisitor)
      Constructs a new CheckClassAdapter. Subclasses must not use this constructor. Instead, they must use the CheckClassAdapter(int, ClassVisitor, boolean) version.
      Parameters:
      classVisitor - the class visitor to which this adapter must delegate calls.

    • CheckClassAdapter

      public CheckClassAdapter(ClassVisitor classVisitor, boolean checkDataFlow)
      Constructs a new CheckClassAdapter. Subclasses must not use this constructor. Instead, they must use the CheckClassAdapter(int, ClassVisitor, boolean) version.
      Parameters:
      classVisitor - the class visitor to which this adapter must delegate calls.
      checkDataFlow - whether to perform basic data flow checks.
      Throws:
      IllegalStateException - If a subclass calls this constructor.

    • CheckClassAdapter

      protected CheckClassAdapter(int api, ClassVisitor classVisitor, boolean checkDataFlow)
      Constructs a new CheckClassAdapter.
      Parameters:
      api - the ASM API version implemented by this visitor. Must be one of the ASMx values in Opcodes.
      classVisitor - the class visitor to which this adapter must delegate calls.
      checkDataFlow - true to perform basic data flow checks, or false to not perform any data flow check (see CheckMethodAdapter).

  • Method Details

    • visit

      public 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 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 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 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()).

    • visitNestMember

      public 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 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()).

    • visitOuterClass

      public 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).

    • visitInnerClass

      public 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 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 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 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.

    • visitAnnotation

      public 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 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 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.

    • visitEnd

      public 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

    • checkClassSignature

      public static void checkClassSignature(String signature)
      Checks a class signature.
      Parameters:
      signature - a string containing the signature that must be checked.

    • checkMethodSignature

      public static void checkMethodSignature(String signature)
      Checks a method signature.
      Parameters:
      signature - a string containing the signature that must be checked.

    • checkFieldSignature

      public static void checkFieldSignature(String signature)
      Checks a field signature.
      Parameters:
      signature - a string containing the signature that must be checked.

    • main

      public static void main(String[] args) throws IOException
      Checks the given class.

      Usage: CheckClassAdapter <binary class name or class file name>

      Parameters:
      args - the command line arguments.
      Throws:
      IOException - if the class cannot be found, or if an IO exception occurs.

    • verify

      public static void verify(ClassReader classReader, boolean printResults, PrintWriter printWriter)
      Checks the given class.
      Parameters:
      classReader - the class to be checked.
      printResults - whether to print the results of the bytecode verification.
      printWriter - where the results (or the stack trace in case of error) must be printed.

    • verify

      public static void verify(ClassReader classReader, ClassLoader loader, boolean printResults, PrintWriter printWriter)
      Checks the given class.
      Parameters:
      classReader - the class to be checked.
      loader - a ClassLoader which will be used to load referenced classes. May be null.
      printResults - whether to print the results of the bytecode verification.
      printWriter - where the results (or the stack trace in case of error) must be printed.