org.objectweb.asm.util

Class CheckClassAdapter

java.lang.Object

org.objectweb.asm.ClassVisitor

org.objectweb.asm.util.CheckClassAdapter

public class CheckClassAdapter
extends org.objectweb.asm.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.

Field Summary

Fields inherited from class org.objectweb.asm.ClassVisitor

api, cv

Constructor Summary

Constructors

Modifier	Constructor and Description
	CheckClassAdapter(org.objectweb.asm.ClassVisitor classVisitor) Constructs a new CheckClassAdapter.
	CheckClassAdapter(org.objectweb.asm.ClassVisitor classVisitor, boolean checkDataFlow) Constructs a new CheckClassAdapter.
protected	CheckClassAdapter(int api, org.objectweb.asm.ClassVisitor classVisitor, boolean checkDataFlow) Constructs a new CheckClassAdapter.

Method Summary

Modifier and Type	Method and Description
static void	checkClassSignature(java.lang.String signature) Checks a class signature.
static void	checkFieldSignature(java.lang.String signature) Checks a field signature.
static void	checkMethodSignature(java.lang.String signature) Checks a method signature.
static void	main(java.lang.String[] args) Checks the given class.
static void	verify(org.objectweb.asm.ClassReader classReader, boolean printResults, java.io.PrintWriter printWriter) Checks the given class.
static void	verify(org.objectweb.asm.ClassReader classReader, java.lang.ClassLoader loader, boolean printResults, java.io.PrintWriter printWriter) Checks the given class.
void	visit(int version, int access, java.lang.String name, java.lang.String signature, java.lang.String superName, java.lang.String[] interfaces)
org.objectweb.asm.AnnotationVisitor	visitAnnotation(java.lang.String descriptor, boolean visible)
void	visitAttribute(org.objectweb.asm.Attribute attribute)
void	visitEnd()
org.objectweb.asm.FieldVisitor	visitField(int access, java.lang.String name, java.lang.String descriptor, java.lang.String signature, java.lang.Object value)
void	visitInnerClass(java.lang.String name, java.lang.String outerName, java.lang.String innerName, int access)
org.objectweb.asm.MethodVisitor	visitMethod(int access, java.lang.String name, java.lang.String descriptor, java.lang.String signature, java.lang.String[] exceptions)
org.objectweb.asm.ModuleVisitor	visitModule(java.lang.String name, int access, java.lang.String version)
void	visitNestHost(java.lang.String nestHost)
void	visitNestMember(java.lang.String nestMember)
void	visitOuterClass(java.lang.String owner, java.lang.String name, java.lang.String descriptor)
void	visitPermittedSubtypeExperimental(java.lang.String permittedSubtype) Deprecated. this API is experimental.
org.objectweb.asm.RecordComponentVisitor	visitRecordComponent(java.lang.String name, java.lang.String descriptor, java.lang.String signature)
void	visitSource(java.lang.String file, java.lang.String debug)
org.objectweb.asm.AnnotationVisitor	visitTypeAnnotation(int typeRef, org.objectweb.asm.TypePath typePath, java.lang.String descriptor, boolean visible)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

CheckClassAdapter

public CheckClassAdapter(org.objectweb.asm.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(org.objectweb.asm.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. This option requires valid maxLocals and maxStack values.

Throws:

java.lang.IllegalStateException - If a subclass calls this constructor.

CheckClassAdapter

protected CheckClassAdapter(int api,
                            org.objectweb.asm.ClassVisitor classVisitor,
                            boolean checkDataFlow)

Constructs a new CheckClassAdapter.

Parameters:

api - the ASM API version implemented by this visitor. Must be one of Opcodes.ASM4, Opcodes.ASM5, Opcodes.ASM6, Opcodes.ASM7 or Opcodes.ASM8.

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). This option requires valid maxLocals and maxStack values.

Method Detail

visit

public void visit(int version,
                  int access,
                  java.lang.String name,
                  java.lang.String signature,
                  java.lang.String superName,
                  java.lang.String[] interfaces)

Overrides:

visit in class org.objectweb.asm.ClassVisitor

visitSource

public void visitSource(java.lang.String file,
                        java.lang.String debug)

Overrides:

visitSource in class org.objectweb.asm.ClassVisitor

visitModule

public org.objectweb.asm.ModuleVisitor visitModule(java.lang.String name,
                                                   int access,
                                                   java.lang.String version)

Overrides:

visitModule in class org.objectweb.asm.ClassVisitor

visitNestHost

public void visitNestHost(java.lang.String nestHost)

Overrides:

visitNestHost in class org.objectweb.asm.ClassVisitor

visitNestMember

public void visitNestMember(java.lang.String nestMember)

Overrides:

visitNestMember in class org.objectweb.asm.ClassVisitor

visitPermittedSubtypeExperimental

@Deprecated
public void visitPermittedSubtypeExperimental(java.lang.String permittedSubtype)

Deprecated. this API is experimental.

Experimental, use at your own risk..

Overrides:

visitPermittedSubtypeExperimental in class org.objectweb.asm.ClassVisitor

Parameters:

permittedSubtype - the internal name of a permitted subtype.

visitOuterClass

public void visitOuterClass(java.lang.String owner,
                            java.lang.String name,
                            java.lang.String descriptor)

Overrides:

visitOuterClass in class org.objectweb.asm.ClassVisitor

visitInnerClass

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

Overrides:

visitInnerClass in class org.objectweb.asm.ClassVisitor

visitRecordComponent

public org.objectweb.asm.RecordComponentVisitor visitRecordComponent(java.lang.String name,
                                                                     java.lang.String descriptor,
                                                                     java.lang.String signature)

Overrides:

visitRecordComponent in class org.objectweb.asm.ClassVisitor

visitField

public org.objectweb.asm.FieldVisitor visitField(int access,
                                                 java.lang.String name,
                                                 java.lang.String descriptor,
                                                 java.lang.String signature,
                                                 java.lang.Object value)

Overrides:

visitField in class org.objectweb.asm.ClassVisitor

visitMethod

public org.objectweb.asm.MethodVisitor visitMethod(int access,
                                                   java.lang.String name,
                                                   java.lang.String descriptor,
                                                   java.lang.String signature,
                                                   java.lang.String[] exceptions)

Overrides:

visitMethod in class org.objectweb.asm.ClassVisitor

visitAnnotation

public org.objectweb.asm.AnnotationVisitor visitAnnotation(java.lang.String descriptor,
                                                           boolean visible)

Overrides:

visitAnnotation in class org.objectweb.asm.ClassVisitor

visitTypeAnnotation

public org.objectweb.asm.AnnotationVisitor visitTypeAnnotation(int typeRef,
                                                               org.objectweb.asm.TypePath typePath,
                                                               java.lang.String descriptor,
                                                               boolean visible)

Overrides:

visitTypeAnnotation in class org.objectweb.asm.ClassVisitor

visitAttribute

public void visitAttribute(org.objectweb.asm.Attribute attribute)

Overrides:

visitAttribute in class org.objectweb.asm.ClassVisitor

visitEnd

public void visitEnd()

Overrides:

visitEnd in class org.objectweb.asm.ClassVisitor

checkClassSignature

public static void checkClassSignature(java.lang.String signature)

Checks a class signature.

Parameters:

signature - a string containing the signature that must be checked.

checkMethodSignature

public static void checkMethodSignature(java.lang.String signature)

Checks a method signature.

Parameters:

signature - a string containing the signature that must be checked.

checkFieldSignature

public static void checkFieldSignature(java.lang.String signature)

Checks a field signature.

Parameters:

signature - a string containing the signature that must be checked.

main

public static void main(java.lang.String[] args)
                 throws java.io.IOException

Checks the given class.

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

Parameters:

args - the command line arguments.

Throws:

java.io.IOException - if the class cannot be found, or if an IO exception occurs.

verify

public static void verify(org.objectweb.asm.ClassReader classReader,
                          boolean printResults,
                          java.io.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(org.objectweb.asm.ClassReader classReader,
                          java.lang.ClassLoader loader,
                          boolean printResults,
                          java.io.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.