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
.
main
public static void main(String[] args)
throws Exception
Checks a given class.
Usage: CheckClassAdapter <fully qualified
class name or class file name>
args
- the command line arguments.
verify
public static void verify(ClassReader cr,
boolean dump,
PrintWriter pw)
Checks a given class
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)
Visits the header of the class.
- visit in interface ClassVisitor
- visit in interface ClassAdapter
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.
visitAnnotation
public AnnotationVisitor visitAnnotation(String desc,
boolean visible)
Visits an annotation of the class.
- visitAnnotation in interface ClassVisitor
- visitAnnotation in interface ClassAdapter
desc
- the class descriptor of the annotation class.visible
- true if the annotation is visible at runtime.
- a visitor to visit the annotation values, or null if
this visitor is not interested in visiting this annotation.
visitEnd
public void visitEnd()
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.
- visitEnd in interface ClassVisitor
- visitEnd in interface ClassAdapter
visitField
public FieldVisitor visitField(int access,
String name,
String desc,
String signature,
Object value)
Visits a field of the class.
- visitField in interface ClassVisitor
- visitField in interface ClassAdapter
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.
- a visitor to visit field annotations and attributes, or
null if this class visitor is not interested in
visiting these annotations and attributes.
visitInnerClass
public void visitInnerClass(String name,
String outerName,
String innerName,
int access)
Visits information about an inner class. This inner class is not
necessarily a member of the class being visited.
- visitInnerClass in interface ClassVisitor
- visitInnerClass in interface ClassAdapter
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.
visitMethod
public MethodVisitor visitMethod(int access,
String name,
String desc,
String signature,
String[] exceptions)
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.
- visitMethod in interface ClassVisitor
- visitMethod in interface ClassAdapter
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.
- 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.
visitOuterClass
public void visitOuterClass(String owner,
String name,
String desc)
Visits the enclosing class of the class. This method must be called only
if the class has an enclosing class.
- visitOuterClass in interface ClassVisitor
- visitOuterClass in interface ClassAdapter
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.
visitSource
public void visitSource(String file,
String debug)
Visits the source of the class.
- visitSource in interface ClassVisitor
- visitSource in interface ClassAdapter
debug
- additional debug information to compute the correspondance
between source and compiled elements of the class. May be
null.