public class CheckClassAdapter extends ClassVisitor
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.
api, cv
Modifier | Constructor and Description |
---|---|
|
CheckClassAdapter(ClassVisitor classVisitor)
Constructs a new
CheckClassAdapter . |
|
CheckClassAdapter(ClassVisitor classVisitor,
boolean checkDataFlow)
Constructs a new
CheckClassAdapter . |
protected |
CheckClassAdapter(int api,
ClassVisitor classVisitor,
boolean checkDataFlow)
Constructs a new
CheckClassAdapter . |
Modifier and Type | Method and Description |
---|---|
static void |
checkClassSignature(String signature)
Checks a class signature.
|
static void |
checkFieldSignature(String signature)
Checks a field signature.
|
static void |
checkMethodSignature(String signature)
Checks a method signature.
|
static void |
main(String[] args)
Checks the given class.
|
static void |
verify(ClassReader classReader,
boolean printResults,
PrintWriter printWriter)
Checks the given class.
|
static void |
verify(ClassReader classReader,
ClassLoader loader,
boolean printResults,
PrintWriter printWriter)
Checks the 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 descriptor,
boolean visible)
Visits an annotation of the class.
|
void |
visitAttribute(Attribute attribute)
Visits a non standard attribute of the class.
|
void |
visitEnd()
Visits the end of the class.
|
FieldVisitor |
visitField(int access,
String name,
String descriptor,
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 descriptor,
String signature,
String[] exceptions)
Visits a method of the class.
|
ModuleVisitor |
visitModule(String name,
int access,
String version)
Visit the module corresponding to the class.
|
void |
visitNestHost(String nestHost)
Visits the nest host class of the class.
|
void |
visitNestMember(String nestMember)
Visits a member of the nest.
|
void |
visitOuterClass(String owner,
String name,
String descriptor)
Visits the enclosing class of the class.
|
void |
visitSource(String file,
String debug)
Visits the source of the class.
|
AnnotationVisitor |
visitTypeAnnotation(int typeRef,
TypePath typePath,
String descriptor,
boolean visible)
Visits an annotation on a type in the class signature.
|
public CheckClassAdapter(ClassVisitor classVisitor)
CheckClassAdapter
. Subclasses must not use this constructor.
Instead, they must use the CheckClassAdapter(int, ClassVisitor, boolean)
version.classVisitor
- the class visitor to which this adapter must delegate calls.public CheckClassAdapter(ClassVisitor classVisitor, boolean checkDataFlow)
CheckClassAdapter
. Subclasses must not use this constructor.
Instead, they must use the CheckClassAdapter(int, ClassVisitor, boolean)
version.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.IllegalStateException
- If a subclass calls this constructor.protected CheckClassAdapter(int api, ClassVisitor classVisitor, boolean checkDataFlow)
CheckClassAdapter
.api
- the ASM API version implemented by this visitor. Must be one of Opcodes.ASM4
, Opcodes.ASM5
, Opcodes.ASM6
or Opcodes.ASM7
.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.public void visit(int version, int access, String name, String signature, String superName, String[] interfaces)
ClassVisitor
visit
in class ClassVisitor
version
- the class version. The minor version is stored in the 16 most significant bits,
and the major version in the 16 least significant bits.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 Type.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 Type.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 Type.getInternalName()
). May be null.public void visitSource(String file, String debug)
ClassVisitor
visitSource
in class ClassVisitor
file
- the name of the source file from which the class was compiled. May be null.debug
- additional debug information to compute the correspondence between source and
compiled elements of the class. May be null.public ModuleVisitor visitModule(String name, int access, String version)
ClassVisitor
visitModule
in class ClassVisitor
name
- the fully qualified name (using dots) of the module.access
- the module access flags, among ACC_OPEN
, ACC_SYNTHETIC
and ACC_MANDATED
.version
- the module version, or null.public void visitNestHost(String nestHost)
ClassVisitor
visitNestHost
in class ClassVisitor
nestHost
- the internal name of the host class of the nest.public void visitNestMember(String nestMember)
ClassVisitor
visitNestMember
in class ClassVisitor
nestMember
- the internal name of a nest member.public void visitOuterClass(String owner, String name, String descriptor)
ClassVisitor
visitOuterClass
in class ClassVisitor
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.descriptor
- the descriptor of the method that contains the class, or null if
the class is not enclosed in a method of its enclosing class.public void visitInnerClass(String name, String outerName, String innerName, int access)
ClassVisitor
visitInnerClass
in class ClassVisitor
name
- the internal name of an inner class (see Type.getInternalName()
).outerName
- the internal name of the class to which the inner class belongs (see Type.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.public FieldVisitor visitField(int access, String name, String descriptor, String signature, Object value)
ClassVisitor
visitField
in class ClassVisitor
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.descriptor
- 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.public MethodVisitor visitMethod(int access, String name, String descriptor, String signature, String[] exceptions)
ClassVisitor
MethodVisitor
instance (or null) each time it is called, i.e., it should not return a previously
returned visitor.visitMethod
in class ClassVisitor
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.descriptor
- 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 Type.getInternalName()
). May be null.public AnnotationVisitor visitAnnotation(String descriptor, boolean visible)
ClassVisitor
visitAnnotation
in class ClassVisitor
descriptor
- the class descriptor of the annotation class.visible
- true if the annotation is visible at runtime.public AnnotationVisitor visitTypeAnnotation(int typeRef, TypePath typePath, String descriptor, boolean visible)
ClassVisitor
visitTypeAnnotation
in class ClassVisitor
typeRef
- a reference to the annotated type. The sort of this type reference must be
TypeReference.CLASS_TYPE_PARAMETER
, TypeReference.CLASS_TYPE_PARAMETER_BOUND
or TypeReference.CLASS_EXTENDS
. See
TypeReference
.typePath
- the path to the annotated type argument, wildcard bound, array element type, or
static inner type within 'typeRef'. May be null if the annotation targets
'typeRef' as a whole.descriptor
- the class descriptor of the annotation class.visible
- true if the annotation is visible at runtime.public void visitAttribute(Attribute attribute)
ClassVisitor
visitAttribute
in class ClassVisitor
attribute
- an attribute.public void visitEnd()
ClassVisitor
visitEnd
in class ClassVisitor
public static void checkClassSignature(String signature)
signature
- a string containing the signature that must be checked.public static void checkMethodSignature(String signature)
signature
- a string containing the signature that must be checked.public static void checkFieldSignature(String signature)
signature
- a string containing the signature that must be checked.public static void main(String[] args) throws IOException
Usage: CheckClassAdapter <binary class name or class file name>
args
- the command line arguments.IOException
- if the class cannot be found, or if an IO exception occurs.public static void verify(ClassReader classReader, boolean printResults, PrintWriter printWriter)
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.public static void verify(ClassReader classReader, ClassLoader loader, boolean printResults, PrintWriter printWriter)
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.Copyright © 2019. All rights reserved.