org.objectweb.gs.asm

Class ClassReader

java.lang.Object

org.objectweb.gs.asm.ClassReader

public class ClassReader
extends Object

A parser to make a ClassVisitor visit a ClassFile structure, as defined in the Java Virtual Machine Specification (JVMS). This class parses the ClassFile content and calls the appropriate visit methods of a given ClassVisitor for each field, method and bytecode instruction encountered.

Author:

Eric Bruneton, Eugene Kuleshov

See Also:

JVMS 4

Field Summary

Fields

Modifier and Type	Field and Description
byte[]	b Deprecated. Use readByte(int) and the other read methods instead. This field will eventually be deleted.
static int	EXPAND_FRAMES A flag to expand the stack map frames.
int	header The offset in bytes of the ClassFile's access_flags field.
static int	SKIP_CODE A flag to skip the Code attributes.
static int	SKIP_DEBUG A flag to skip the SourceFile, SourceDebugExtension, LocalVariableTable, LocalVariableTypeTable, LineNumberTable and MethodParameters attributes.
static int	SKIP_FRAMES A flag to skip the StackMap and StackMapTable attributes.

Constructor Summary

Constructors

Constructor and Description
ClassReader(byte[] classFile) Constructs a new ClassReader object.
ClassReader(byte[] classFileBuffer, int classFileOffset, int classFileLength) Constructs a new ClassReader object.
ClassReader(InputStream inputStream) Constructs a new ClassReader object.
ClassReader(String className) Constructs a new ClassReader object.

Method Summary

Modifier and Type	Method and Description
void	accept(ClassVisitor classVisitor, Attribute[] attributePrototypes, int parsingOptions) Makes the given visitor visit the JVMS ClassFile structure passed to the constructor of this ClassReader.
void	accept(ClassVisitor classVisitor, int parsingOptions) Makes the given visitor visit the JVMS ClassFile structure passed to the constructor of this ClassReader.
int	getAccess() Returns the class's access flags (see Opcodes).
String	getClassName() Returns the internal name of the class (see Type.getInternalName()).
String[]	getInterfaces() Returns the internal names of the implemented interfaces (see Type.getInternalName()).
int	getItem(int constantPoolEntryIndex) Returns the start offset in this ClassReader of a JVMS 'cp_info' structure (i.e.
int	getItemCount() Returns the number of entries in the class's constant pool table.
int	getMaxStringLength() Returns a conservative estimate of the maximum length of the strings contained in the class's constant pool table.
String	getSuperName() Returns the internal name of the super class (see Type.getInternalName()).
int	readByte(int offset) Reads a byte value in this ClassReader.
protected void	readBytecodeInstructionOffset(int bytecodeOffset) Handles the bytecode offset of the next instruction to be visited in accept(ClassVisitor, int).
String	readClass(int offset, char[] charBuffer) Reads a CONSTANT_Class constant pool entry in this ClassReader.
Object	readConst(int constantPoolEntryIndex, char[] charBuffer) Reads a numeric or string constant pool entry in this ClassReader.
int	readInt(int offset) Reads a signed int value in this ClassReader.
protected Label	readLabel(int bytecodeOffset, Label[] labels) Returns the label corresponding to the given bytecode offset.
long	readLong(int offset) Reads a signed long value in this ClassReader.
String	readModule(int offset, char[] charBuffer) Reads a CONSTANT_Module constant pool entry in this ClassReader.
String	readPackage(int offset, char[] charBuffer) Reads a CONSTANT_Package constant pool entry in this ClassReader.
short	readShort(int offset) Reads a signed short value in this ClassReader.
int	readUnsignedShort(int offset) Reads an unsigned short value in this ClassReader.
String	readUTF8(int offset, char[] charBuffer) Reads a CONSTANT_Utf8 constant pool entry in this ClassReader.

Methods inherited from class java.lang.Object

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

Field Detail

SKIP_CODE

public static final int SKIP_CODE

A flag to skip the Code attributes. If this flag is set the Code attributes are neither parsed nor visited.

See Also:

Constant Field Values

SKIP_DEBUG

public static final int SKIP_DEBUG

A flag to skip the SourceFile, SourceDebugExtension, LocalVariableTable, LocalVariableTypeTable, LineNumberTable and MethodParameters attributes. If this flag is set these attributes are neither parsed nor visited (i.e. ClassVisitor.visitSource(java.lang.String, java.lang.String), MethodVisitor.visitLocalVariable(java.lang.String, java.lang.String, java.lang.String, org.objectweb.gs.asm.Label, org.objectweb.gs.asm.Label, int), MethodVisitor.visitLineNumber(int, org.objectweb.gs.asm.Label) and MethodVisitor.visitParameter(java.lang.String, int) are not called).

See Also:

Constant Field Values

SKIP_FRAMES

public static final int SKIP_FRAMES

A flag to skip the StackMap and StackMapTable attributes. If this flag is set these attributes are neither parsed nor visited (i.e. MethodVisitor.visitFrame(int, int, java.lang.Object[], int, java.lang.Object[]) is not called). This flag is useful when the ClassWriter.COMPUTE_FRAMES option is used: it avoids visiting frames that will be ignored and recomputed from scratch.

See Also:

Constant Field Values

EXPAND_FRAMES

public static final int EXPAND_FRAMES

A flag to expand the stack map frames. By default stack map frames are visited in their original format (i.e. "expanded" for classes whose version is less than V1_6, and "compressed" for the other classes). If this flag is set, stack map frames are always visited in expanded format (this option adds a decompression/compression step in ClassReader and ClassWriter which degrades performance quite a lot).

See Also:

Constant Field Values

b

@Deprecated
public final byte[] b

Deprecated. Use readByte(int) and the other read methods instead. This field will eventually be deleted.

A byte array containing the JVMS ClassFile structure to be parsed.

header

public final int header

The offset in bytes of the ClassFile's access_flags field.

Constructor Detail

ClassReader

public ClassReader(byte[] classFile)

Constructs a new ClassReader object.

Parameters:

classFile - the JVMS ClassFile structure to be read.

ClassReader

public ClassReader(byte[] classFileBuffer,
                   int classFileOffset,
                   int classFileLength)

Constructs a new ClassReader object.

Parameters:

classFileBuffer - a byte array containing the JVMS ClassFile structure to be read.

classFileOffset - the offset in byteBuffer of the first byte of the ClassFile to be read.

classFileLength - the length in bytes of the ClassFile to be read.

ClassReader

public ClassReader(InputStream inputStream)
            throws IOException

Constructs a new ClassReader object.

Parameters:

inputStream - an input stream of the JVMS ClassFile structure to be read. This input stream must contain nothing more than the ClassFile structure itself. It is read from its current position to its end.

Throws:

IOException - if a problem occurs during reading.

ClassReader

public ClassReader(String className)
            throws IOException

Constructs a new ClassReader object.

Parameters:

className - the fully qualified name of the class to be read. The ClassFile structure is retrieved with the current class loader's ClassLoader.getSystemResourceAsStream(java.lang.String).

Throws:

IOException - if an exception occurs during reading.

Method Detail

getAccess

public int getAccess()

Returns the class's access flags (see Opcodes). This value may not reflect Deprecated and Synthetic flags when bytecode is before 1.5 and those flags are represented by attributes.

Returns:

the class access flags.

See Also:

ClassVisitor.visit(int, int, String, String, String, String[])

getClassName

public String getClassName()

Returns the internal name of the class (see Type.getInternalName()).

Returns:

the internal class name.

See Also:

ClassVisitor.visit(int, int, String, String, String, String[])

getSuperName

public String getSuperName()

Returns the internal name of the super class (see Type.getInternalName()). For interfaces, the super class is Object.

Returns:

the internal name of the super class, or null for Object class.

See Also:

ClassVisitor.visit(int, int, String, String, String, String[])

getInterfaces

public String[] getInterfaces()

Returns the internal names of the implemented interfaces (see Type.getInternalName()).

Returns:

the internal names of the directly implemented interfaces. Inherited implemented interfaces are not returned.

See Also:

ClassVisitor.visit(int, int, String, String, String, String[])

accept

public void accept(ClassVisitor classVisitor,
                   int parsingOptions)

Makes the given visitor visit the JVMS ClassFile structure passed to the constructor of this ClassReader.

Parameters:

classVisitor - the visitor that must visit this class.

parsingOptions - the options to use to parse this class. One or more of SKIP_CODE, SKIP_DEBUG, SKIP_FRAMES or EXPAND_FRAMES.

accept

public void accept(ClassVisitor classVisitor,
                   Attribute[] attributePrototypes,
                   int parsingOptions)

Makes the given visitor visit the JVMS ClassFile structure passed to the constructor of this ClassReader.

Parameters:

classVisitor - the visitor that must visit this class.

attributePrototypes - prototypes of the attributes that must be parsed during the visit of the class. Any attribute whose type is not equal to the type of one the prototypes will not be parsed: its byte array value will be passed unchanged to the ClassWriter. This may corrupt it if this value contains references to the constant pool, or has syntactic or semantic links with a class element that has been transformed by a class adapter between the reader and the writer.

parsingOptions - the options to use to parse this class. One or more of SKIP_CODE, SKIP_DEBUG, SKIP_FRAMES or EXPAND_FRAMES.

readBytecodeInstructionOffset

protected void readBytecodeInstructionOffset(int bytecodeOffset)

Handles the bytecode offset of the next instruction to be visited in accept(ClassVisitor, int). This method is called just before the instruction and before its associated label and stack map frame, if any. The default implementation of this method does nothing. Subclasses can override this method to store the argument in a mutable field, for instance, so that MethodVisitor instances can get the bytecode offset of each visited instruction (if so, the usual concurrency issues related to mutable data should be addressed).

Parameters:

bytecodeOffset - the bytecode offset of the next instruction to be visited.

readLabel

protected Label readLabel(int bytecodeOffset,
                          Label[] labels)

Returns the label corresponding to the given bytecode offset. The default implementation of this method creates a label for the given offset if it has not been already created.

Parameters:

bytecodeOffset - a bytecode offset in a method.

labels - the already created labels, indexed by their offset. If a label already exists for bytecodeOffset this method must not create a new one. Otherwise it must store the new label in this array.

Returns:

a non null Label, which must be equal to labels[bytecodeOffset].

getItemCount

public int getItemCount()

Returns the number of entries in the class's constant pool table.

Returns:

the number of entries in the class's constant pool table.

getItem

public int getItem(int constantPoolEntryIndex)

Returns the start offset in this ClassReader of a JVMS 'cp_info' structure (i.e. a constant pool entry), plus one. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

constantPoolEntryIndex - the index a constant pool entry in the class's constant pool table.

Returns:

the start offset in this ClassReader of the corresponding JVMS 'cp_info' structure, plus one.

getMaxStringLength

public int getMaxStringLength()

Returns a conservative estimate of the maximum length of the strings contained in the class's constant pool table.

Returns:

a conservative estimate of the maximum length of the strings contained in the class's constant pool table.

readByte

public int readByte(int offset)

Reads a byte value in this ClassReader. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

offset - the start offset of the value to be read in this ClassReader.

Returns:

the read value.

readUnsignedShort

public int readUnsignedShort(int offset)

Reads an unsigned short value in this ClassReader. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

offset - the start index of the value to be read in this ClassReader.

Returns:

the read value.

readShort

public short readShort(int offset)

Reads a signed short value in this ClassReader. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

offset - the start offset of the value to be read in this ClassReader.

Returns:

the read value.

readInt

public int readInt(int offset)

Reads a signed int value in this ClassReader. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

offset - the start offset of the value to be read in this ClassReader.

Returns:

the read value.

readLong

public long readLong(int offset)

Reads a signed long value in this ClassReader. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

offset - the start offset of the value to be read in this ClassReader.

Returns:

the read value.

readUTF8

public String readUTF8(int offset,
                       char[] charBuffer)

Reads a CONSTANT_Utf8 constant pool entry in this ClassReader. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

offset - the start offset of an unsigned short value in this ClassReader, whose value is the index of a CONSTANT_Utf8 entry in the class's constant pool table.

charBuffer - the buffer to be used to read the string. This buffer must be sufficiently large. It is not automatically resized.

Returns:

the String corresponding to the specified CONSTANT_Utf8 entry.

readClass

public String readClass(int offset,
                        char[] charBuffer)

Reads a CONSTANT_Class constant pool entry in this ClassReader. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

offset - the start offset of an unsigned short value in this ClassReader, whose value is the index of a CONSTANT_Class entry in class's constant pool table.

charBuffer - the buffer to be used to read the item. This buffer must be sufficiently large. It is not automatically resized.

Returns:

the String corresponding to the specified CONSTANT_Class entry.

readModule

public String readModule(int offset,
                         char[] charBuffer)

Reads a CONSTANT_Module constant pool entry in this ClassReader. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

offset - the start offset of an unsigned short value in this ClassReader, whose value is the index of a CONSTANT_Module entry in class's constant pool table.

charBuffer - the buffer to be used to read the item. This buffer must be sufficiently large. It is not automatically resized.

Returns:

the String corresponding to the specified CONSTANT_Module entry.

readPackage

public String readPackage(int offset,
                          char[] charBuffer)

Reads a CONSTANT_Package constant pool entry in this ClassReader. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

offset - the start offset of an unsigned short value in this ClassReader, whose value is the index of a CONSTANT_Package entry in class's constant pool table.

charBuffer - the buffer to be used to read the item. This buffer must be sufficiently large. It is not automatically resized.

Returns:

the String corresponding to the specified CONSTANT_Package entry.

readConst

public Object readConst(int constantPoolEntryIndex,
                        char[] charBuffer)

Reads a numeric or string constant pool entry in this ClassReader. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

constantPoolEntryIndex - the index of a CONSTANT_Integer, CONSTANT_Float, CONSTANT_Long, CONSTANT_Double, CONSTANT_Class, CONSTANT_String, CONSTANT_MethodType, CONSTANT_MethodHandle or CONSTANT_Dynamic entry in the class's constant pool.

charBuffer - the buffer to be used to read strings. This buffer must be sufficiently large. It is not automatically resized.

Returns:

the Integer, Float, Long, Double, String, Type, Handle or ConstantDynamic corresponding to the specified constant pool entry.