Class CheckClassAdapter

java.lang.Object
org.objectweb.asm.ClassAdapter
org.objectweb.asm.util.CheckClassAdapter
All Implemented Interfaces:
ClassVisitor
public class CheckClassAdapter extends ClassAdapter
A ClassAdapter 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 transformed bytecode is sane. For example: 

  InputStream is = ...; // get bytes for the source class
  ClassReader cr = new ClassReader(is);
  ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_MAXS);
  ClassVisitor cv = new MyClassAdapter(new CheckClassAdapter(cw));
  cr.accept(cv, 0);

  StringWriter sw = new StringWriter();
  PrintWriter pw = new PrintWriter(sw);
  CheckClassAdapter.verify(new ClassReader(cw.toByteArray()), false, pw);
  assertTrue(sw.toString(), sw.toString().length()==0);
Above code runs transformed bytecode trough the CheckClassAdapter. It won't be exactly the same verification as JVM does, but it run data flow analysis for the code of each method and checks that expectations are met for each method instruction.

If method bytecode has errors, assertion text will show the erroneous instruction number and dump of the failed method with information about locals and stack slot 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:289)
  at org.objectweb.asm.util.CheckClassAdapter.verify(CheckClassAdapter.java:135)
...
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. (I)V
...
In the above output you can see that variable 1 loaded by ILOAD 1 instruction at position 00071 is not initialized. You can also see that at the beginning of the method (code inserted by the transformation) variable 2 is initialized.

Note that when used like that, CheckClassAdapter.verify() can trigger additional class loading, because it is using SimpleVerifier.

Author:
Eric Bruneton

  • Constructor Details

    • CheckClassAdapter

      public CheckClassAdapter(ClassVisitor cv)
      Constructs a new CheckClassAdapter.
      Parameters:
      cv - the class visitor to which this adapter must delegate calls.

    • CheckClassAdapter

      public CheckClassAdapter(ClassVisitor cv, boolean checkDataFlow)
      Constructs a new CheckClassAdapter.
      Parameters:
      cv - 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). This option requires valid maxLocals and maxStack values.

  • Method Details

    • main

      public static void main(String[] args) throws Exception
      Checks a given class.

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

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

    • verify

      public static void verify(ClassReader cr, ClassLoader loader, boolean dump, PrintWriter pw)
      Checks a given class
      Parameters:
      cr - a ClassReader that contains bytecode for the analysis.
      loader - a ClassLoader which will be used to load referenced classes. This is useful if you are verifiying multiple interdependent classes.
      dump - true if bytecode should be printed out not only when errors are found.
      pw - write where results going to be printed

    • verify

      public static void verify(ClassReader cr, boolean dump, PrintWriter pw)
      Checks a given class
      Parameters:
      cr - a ClassReader that contains bytecode for the analysis.
      dump - true if bytecode should be printed out not only when errors are found.
      pw - write where results going to be printed

    • visit

      public void visit(int version, int access, String name, String signature, String superName, String[] interfaces)
      Description copied from interface: ClassVisitor
      Visits the header of the class.
      Specified by:
      visit in interface ClassVisitor
      Overrides:
      visit in class ClassAdapter
      Parameters:
      version - the class version.
      access - the class's access flags (see Opcodes). This parameter also indicates if the class is deprecated.
      name - the internal name of the class (see 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 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 getInternalName). May be null.

    • visitSource

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

    • visitOuterClass

      public void visitOuterClass(String owner, String name, String desc)
      Description copied from interface: ClassVisitor
      Visits the enclosing class of the class. This method must be called only if the class has an enclosing class.
      Specified by:
      visitOuterClass in interface ClassVisitor
      Overrides:
      visitOuterClass in class ClassAdapter
      Parameters:
      owner - internal name of the enclosing class of the class.
      name - the name of the method that contains the class, or null if the class is not enclosed in a method of its enclosing class.
      desc - the descriptor of the method that contains the class, or null if the class is not enclosed in a method of its enclosing class.

    • visitInnerClass

      public void visitInnerClass(String name, String outerName, String innerName, int access)
      Description copied from interface: ClassVisitor
      Visits information about an inner class. This inner class is not necessarily a member of the class being visited.
      Specified by:
      visitInnerClass in interface ClassVisitor
      Overrides:
      visitInnerClass in class ClassAdapter
      Parameters:
      name - the internal name of an inner class (see getInternalName).
      outerName - the internal name of the class to which the inner class belongs (see getInternalName). May be null for not member classes.
      innerName - the (simple) name of the inner class inside its enclosing class. May be null for anonymous inner classes.
      access - the access flags of the inner class as originally declared in the enclosing class.

    • visitField

      public FieldVisitor visitField(int access, String name, String desc, String signature, Object value)
      Description copied from interface: ClassVisitor
      Visits a field of the class.
      Specified by:
      visitField in interface ClassVisitor
      Overrides:
      visitField in class ClassAdapter
      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.
      desc - 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 desc, String signature, String[] exceptions)
      Description copied from interface: 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.
      Specified by:
      visitMethod in interface ClassVisitor
      Overrides:
      visitMethod in class ClassAdapter
      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.
      desc - 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 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 desc, boolean visible)
      Description copied from interface: ClassVisitor
      Visits an annotation of the class.
      Specified by:
      visitAnnotation in interface ClassVisitor
      Overrides:
      visitAnnotation in class ClassAdapter
      Parameters:
      desc - 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 attr)
      Description copied from interface: ClassVisitor
      Visits a non standard attribute of the class.
      Specified by:
      visitAttribute in interface ClassVisitor
      Overrides:
      visitAttribute in class ClassAdapter
      Parameters:
      attr - an attribute.

    • visitEnd

      public void visitEnd()
      Description copied from interface: 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.
      Specified by:
      visitEnd in interface ClassVisitor
      Overrides:
      visitEnd in class ClassAdapter