org.objectweb.asm.util

Class CheckClassAdapter

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 Summary
CheckClassAdapter(ClassVisitor cv)
Constructs a new CheckClassAdapter.
CheckClassAdapter(ClassVisitor cv, boolean checkDataFlow)
Constructs a new CheckClassAdapter.
Method Summary
static voidmain(String[] args)
Checks a given class.
static voidverify(ClassReader cr, ClassLoader loader, boolean dump, PrintWriter pw)
Checks a given class
static voidverify(ClassReader cr, boolean dump, PrintWriter pw)
Checks a given class
voidvisit(int version, int access, String name, String signature, String superName, String[] interfaces)
AnnotationVisitorvisitAnnotation(String desc, boolean visible)
voidvisitAttribute(Attribute attr)
voidvisitEnd()
FieldVisitorvisitField(int access, String name, String desc, String signature, Object value)
voidvisitInnerClass(String name, String outerName, String innerName, int access)
MethodVisitorvisitMethod(int access, String name, String desc, String signature, String[] exceptions)
voidvisitOuterClass(String owner, String name, String desc)
voidvisitSource(String file, String debug)

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)
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)

visitAnnotation

public AnnotationVisitor visitAnnotation(String desc, boolean visible)

visitAttribute

public void visitAttribute(Attribute attr)

visitEnd

public void visitEnd()

visitField

public FieldVisitor visitField(int access, String name, String desc, String signature, Object value)

visitInnerClass

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

visitMethod

public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions)

visitOuterClass

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

visitSource

public void visitSource(String file, String debug)