org.objectweb.asm.util
Class CheckClassAdapter

java.lang.Object
  extended by org.objectweb.asm.ClassAdapter
      extended by 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

Field Summary
 
Fields inherited from class org.objectweb.asm.ClassAdapter
cv
 
Constructor Summary
CheckClassAdapter(ClassVisitor cv)
          Constructs a new CheckClassAdapter.
CheckClassAdapter(ClassVisitor cv, boolean checkDataFlow)
          Constructs a new CheckClassAdapter.
 
Method Summary
static void main(String[] args)
          Checks a given class.
static void verify(ClassReader cr, boolean dump, PrintWriter pw)
          Checks a given class
static void verify(ClassReader cr, ClassLoader loader, boolean dump, PrintWriter pw)
          Checks a given class
 void visit(int version, int access, String name, String signature, String superName, String[] interfaces)
          Visits the header of the class.
 AnnotationVisitor visitAnnotation(String desc, boolean visible)
          Visits an annotation of the class.
 void visitAttribute(Attribute attr)
          Visits a non standard attribute of the class.
 void visitEnd()
          Visits the end of the class.
 FieldVisitor visitField(int access, String name, String desc, String signature, Object value)
          Visits a field of the class.
 void visitInnerClass(String name, String outerName, String innerName, int access)
          Visits information about an inner class.
 MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions)
          Visits a method of the class.
 void visitOuterClass(String owner, String name, String desc)
          Visits the enclosing class of the class.
 void visitSource(String file, String debug)
          Visits the source of the class.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

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).
Method Detail

main

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

Usage: CheckClassAdapter <fully qualified 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