org.objectweb.gs.asm

Class ClassReader

java.lang.Object

org.objectweb.gs.asm.ClassReader

public class ClassReader
extends Object

A Java class parser to make a ClassVisitor visit an existing class. This class parses a byte array conforming to the Java class file format and calls the appropriate visit methods of a given class visitor for each field, method and bytecode instruction encountered.

Author:

Eric Bruneton, Eugene Kuleshov

Field Summary

Fields

Modifier and Type	Field and Description
byte[]	b The class to be parsed.
static int	EXPAND_FRAMES Flag to expand the stack map frames.
int	header Start index of the class header information (access, name...) in b.
static int	SKIP_CODE Flag to skip method code.
static int	SKIP_DEBUG Flag to skip the debug information in the class.
static int	SKIP_FRAMES Flag to skip the stack map frames in the class.

Constructor Summary

Constructors

Constructor and Description
ClassReader(byte[] b) Constructs a new ClassReader object.
ClassReader(byte[] b, int off, int len) Constructs a new ClassReader object.
ClassReader(InputStream is) Constructs a new ClassReader object.
ClassReader(String name) Constructs a new ClassReader object.

Method Summary

Modifier and Type	Method and Description
void	accept(ClassVisitor classVisitor, Attribute[] attrs, int flags) Makes the given visitor visit the Java class of this ClassReader.
void	accept(ClassVisitor classVisitor, int flags) Makes the given visitor visit the Java class of this ClassReader.
int	getAccess() Returns the class's access flags (see Opcodes).
String	getClassName() Returns the internal name of the class (see getInternalName).
String[]	getInterfaces() Returns the internal names of the class's interfaces (see getInternalName).
int	getItem(int item) Returns the start index of the constant pool item in b, plus one.
String	getSuperName() Returns the internal of name of the super class (see getInternalName).
int	readByte(int index) Reads a byte value in b.
String	readClass(int index, char[] buf) Reads a class constant pool item in b.
Object	readConst(int item, char[] buf) Reads a numeric or string constant pool item in b.
int	readInt(int index) Reads a signed int value in b.
protected Label	readLabel(int offset, Label[] labels) Returns the label corresponding to the given offset.
long	readLong(int index) Reads a signed long value in b.
short	readShort(int index) Reads a signed short value in b.
int	readUnsignedShort(int index) Reads an unsigned short value in b.
String	readUTF8(int index, char[] buf) Reads an UTF8 string constant pool item in b.

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

Flag to skip method code. If this class is set CODE attribute won't be visited. This can be used, for example, to retrieve annotations for methods and method parameters.

See Also:

Constant Field Values

SKIP_DEBUG

public static final int SKIP_DEBUG

Flag to skip the debug information in the class. If this flag is set the debug information of the class is not visited, i.e. the visitLocalVariable and visitLineNumber methods will not be called.

See Also:

Constant Field Values

SKIP_FRAMES

public static final int SKIP_FRAMES

Flag to skip the stack map frames in the class. If this flag is set the stack map frames of the class is not visited, i.e. the visitFrame method will not be 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 in the class writer.

See Also:

Constant Field Values

EXPAND_FRAMES

public static final int EXPAND_FRAMES

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/recompression step in ClassReader and ClassWriter which degrades performances quite a lot).

See Also:

Constant Field Values

b

public final byte[] b

The class to be parsed. The content of this array must not be modified. This field is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

header

public final int header

Start index of the class header information (access, name...) in b.

Constructor Detail

ClassReader

public ClassReader(byte[] b)

Constructs a new ClassReader object.

Parameters:

b - the bytecode of the class to be read.

ClassReader

public ClassReader(byte[] b,
                   int off,
                   int len)

Constructs a new ClassReader object.

Parameters:

b - the bytecode of the class to be read.

off - the start offset of the class data.

len - the length of the class data.

ClassReader

public ClassReader(InputStream is)
            throws IOException

Constructs a new ClassReader object.

Parameters:

is - an input stream from which to read the class.

Throws:

IOException - if a problem occurs during reading.

ClassReader

public ClassReader(String name)
            throws IOException

Constructs a new ClassReader object.

Parameters:

name - the fully qualified name of the class to be read.

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 getInternalName).

Returns:

the internal class name

See Also:

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

getSuperName

public String getSuperName()

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

Returns:

the internal name of 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 class's interfaces (see getInternalName).

Returns:

the array of internal names for all implemented interfaces or null.

See Also:

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

accept

public void accept(ClassVisitor classVisitor,
                   int flags)

Makes the given visitor visit the Java class of this ClassReader. This class is the one specified in the constructor (see ClassReader).

Parameters:

classVisitor - the visitor that must visit this class.

flags - option flags that can be used to modify the default behavior of this class. See SKIP_DEBUG, EXPAND_FRAMES, SKIP_FRAMES, SKIP_CODE.

accept

public void accept(ClassVisitor classVisitor,
                   Attribute[] attrs,
                   int flags)

Makes the given visitor visit the Java class of this ClassReader. This class is the one specified in the constructor (see ClassReader).

Parameters:

classVisitor - the visitor that must visit this class.

attrs - 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.

flags - option flags that can be used to modify the default behavior of this class. See SKIP_DEBUG, EXPAND_FRAMES, SKIP_FRAMES, SKIP_CODE.

readLabel

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

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

Parameters:

offset - a bytecode offset in a method.

labels - the already created labels, indexed by their offset. If a label already exists for offset 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[offset].

getItem

public int getItem(int item)

Returns the start index of the constant pool item in b, plus one. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

item - the index a constant pool item.

Returns:

the start index of the constant pool item in b, plus one.

readByte

public int readByte(int index)

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

Parameters:

index - the start index of the value to be read in b.

Returns:

the read value.

readUnsignedShort

public int readUnsignedShort(int index)

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

Parameters:

index - the start index of the value to be read in b.

Returns:

the read value.

readShort

public short readShort(int index)

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

Parameters:

index - the start index of the value to be read in b.

Returns:

the read value.

readInt

public int readInt(int index)

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

Parameters:

index - the start index of the value to be read in b.

Returns:

the read value.

readLong

public long readLong(int index)

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

Parameters:

index - the start index of the value to be read in b.

Returns:

the read value.

readUTF8

public String readUTF8(int index,
                       char[] buf)

Reads an UTF8 string constant pool item in b. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:

index - the start index of an unsigned short value in b, whose value is the index of an UTF8 constant pool item.

buf - 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 UTF8 item.

readClass

public String readClass(int index,
                        char[] buf)

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

Parameters:

index - the start index of an unsigned short value in b, whose value is the index of a class constant pool item.

buf - 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 class item.

readConst

public Object readConst(int item,
                        char[] buf)

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

Parameters:

item - the index of a constant pool item.

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

Returns:

the Integer, Float, Long, Double, String or Type corresponding to the given constant pool item.