org.springframework.asm

Class ClassReader

java.lang.Object

org.springframework.asm.ClassReader

public class ClassReader
extends java.lang.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
(package private) static boolean	ANNOTATIONS True to enable annotations support.
byte[]	b The class to be parsed.
static int	EXPAND_FRAMES Flag to expand the stack map frames.
(package private) static boolean	FRAMES True to enable stack map frames support.
int	header Start index of the class header information (access, name...) in b.
private int[]	items The start index of each constant pool item in b, plus one.
private int	maxStringLength Maximum length of the strings contained in the constant pool of the class.
(package private) static boolean	RESIZE True to enable JSR_W and GOTO_W support.
(package private) static boolean	SIGNATURES True to enable signatures support.
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.
private java.lang.String[]	strings The String objects corresponding to the CONSTANT_Utf8 items.
(package private) static boolean	WRITER True to enable bytecode writing support.

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(java.io.InputStream is) Constructs a new ClassReader object.
ClassReader(java.lang.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 .
private void	copyBootstrapMethods(ClassWriter classWriter, Item[] items, char[] c) Copies the bootstrap method data into the given ClassWriter.
(package private) void	copyPool(ClassWriter classWriter) Copies the constant pool data into the given ClassWriter.
int	getAccess() Returns the class's access flags (see Opcodes).
private int	getAttributes() Returns the start index of the attribute_info structure of this class.
java.lang.String	getClassName() Returns the internal name of the class (see getInternalName).
private void	getImplicitFrame(Context frame) Computes the implicit frame of the method currently being parsed (as defined in the given Context) and stores it in the given context.
java.lang.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.
int	getItemCount() Returns the number of constant pool items in b.
int	getMaxStringLength() Returns the maximum length of the strings contained in the constant pool of the class.
java.lang.String	getSuperName() Returns the internal of name of the super class (see getInternalName).
private int	readAnnotationTarget(Context context, int u) Parses the header of a type annotation to extract its target_type and target_path (the result is stored in the given context), and returns the start offset of the rest of the type_annotation structure (i.e.
private int	readAnnotationValue(int v, char[] buf, java.lang.String name, AnnotationVisitor av) Reads a value of an annotation and makes the given visitor visit it.
private int	readAnnotationValues(int v, char[] buf, boolean named, AnnotationVisitor av) Reads the values of an annotation and makes the given visitor visit them.
private Attribute	readAttribute(Attribute[] attrs, java.lang.String type, int off, int len, char[] buf, int codeOff, Label[] labels) Reads an attribute in b.
int	readByte(int index) Reads a byte value in b.
private static byte[]	readClass(java.io.InputStream is, boolean close) Reads the bytecode of a class.
java.lang.String	readClass(int index, char[] buf) Reads a class constant pool item in b.
private void	readCode(MethodVisitor mv, Context context, int u) Reads the bytecode of a method and makes the given visitor visit it.
java.lang.Object	readConst(int item, char[] buf) Reads a numeric or string constant pool item in b.
private int	readField(ClassVisitor classVisitor, Context context, int u) Reads a field and makes the given visitor visit it.
private int	readFrame(int stackMap, boolean zip, boolean unzip, Context frame) Reads a stack map frame and stores the result in the given Context object.
private int	readFrameType(java.lang.Object[] frame, int index, int v, char[] buf, Label[] labels) Reads a stack map frame type and stores it at the given index in the given array.
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.
private int	readMethod(ClassVisitor classVisitor, Context context, int u) Reads a method and makes the given visitor visit it.
private void	readParameterAnnotations(MethodVisitor mv, Context context, int v, boolean visible) Reads parameter annotations and makes the given visitor visit them.
short	readShort(int index) Reads a signed short value in b.
private int[]	readTypeAnnotations(MethodVisitor mv, Context context, int u, boolean visible) Parses a type annotation table to find the labels, and to visit the try catch block annotations.
int	readUnsignedShort(int index) Reads an unsigned short value in b.
private java.lang.String	readUTF(int index, int utfLen, char[] buf) Reads UTF8 string in b.
java.lang.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

SIGNATURES

static final boolean SIGNATURES

True to enable signatures support.

See Also:

Constant Field Values

ANNOTATIONS

static final boolean ANNOTATIONS

True to enable annotations support.

See Also:

Constant Field Values

FRAMES

static final boolean FRAMES

True to enable stack map frames support.

See Also:

Constant Field Values

WRITER

static final boolean WRITER

True to enable bytecode writing support.

See Also:

Constant Field Values

RESIZE

static final boolean RESIZE

True to enable JSR_W and GOTO_W support.

See Also:

Constant Field Values

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.

items

private final int[] items

The start index of each constant pool item in b, plus one. The one byte offset skips the constant pool item tag that indicates its type.

strings

private final java.lang.String[] strings

The String objects corresponding to the CONSTANT_Utf8 items. This cache avoids multiple parsing of a given CONSTANT_Utf8 constant pool item, which GREATLY improves performances (by a factor 2 to 3). This caching strategy could be extended to all constant pool items, but its benefit would not be so great for these items (because they are much less expensive to parse than CONSTANT_Utf8 items).

maxStringLength

private final int maxStringLength

Maximum length of the strings contained in the constant pool of the class.

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(java.io.InputStream is)
            throws java.io.IOException

Constructs a new ClassReader object.

Parameters:

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

Throws:

java.io.IOException - if a problem occurs during reading.

ClassReader

public ClassReader(java.lang.String name)
            throws java.io.IOException

Constructs a new ClassReader object.

Parameters:

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

Throws:

java.io.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 java.lang.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 java.lang.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 java.lang.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[])

copyPool

void copyPool(ClassWriter classWriter)

Copies the constant pool data into the given ClassWriter. Should be called before the accept(ClassVisitor,int) method.

Parameters:

classWriter - the ClassWriter to copy constant pool into.

copyBootstrapMethods

private void copyBootstrapMethods(ClassWriter classWriter,
                                  Item[] items,
                                  char[] c)

Copies the bootstrap method data into the given ClassWriter. Should be called before the accept(ClassVisitor,int) method.

Parameters:

classWriter - the ClassWriter to copy bootstrap methods into.

readClass

private static byte[] readClass(java.io.InputStream is,
                                boolean close)
                         throws java.io.IOException

Reads the bytecode of a class.

Parameters:

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

close - true to close the input stream after reading.

Returns:

the bytecode read from the given input stream.

Throws:

java.io.IOException - if a problem occurs during reading.

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.

readField

private int readField(ClassVisitor classVisitor,
                      Context context,
                      int u)

Reads a field and makes the given visitor visit it.

Parameters:

classVisitor - the visitor that must visit the field.

context - information about the class being parsed.

u - the start offset of the field in the class file.

Returns:

the offset of the first byte following the field in the class.

readMethod

private int readMethod(ClassVisitor classVisitor,
                       Context context,
                       int u)

Reads a method and makes the given visitor visit it.

Parameters:

classVisitor - the visitor that must visit the method.

context - information about the class being parsed.

u - the start offset of the method in the class file.

Returns:

the offset of the first byte following the method in the class.

readCode

private void readCode(MethodVisitor mv,
                      Context context,
                      int u)

Reads the bytecode of a method and makes the given visitor visit it.

Parameters:

mv - the visitor that must visit the method's code.

context - information about the class being parsed.

u - the start offset of the code attribute in the class file.

readTypeAnnotations

private int[] readTypeAnnotations(MethodVisitor mv,
                                  Context context,
                                  int u,
                                  boolean visible)

Parses a type annotation table to find the labels, and to visit the try catch block annotations.

Parameters:

u - the start offset of a type annotation table.

mv - the method visitor to be used to visit the try catch block annotations.

context - information about the class being parsed.

visible - if the type annotation table to parse contains runtime visible annotations.

Returns:

the start offset of each type annotation in the parsed table.

readAnnotationTarget

private int readAnnotationTarget(Context context,
                                 int u)

Parses the header of a type annotation to extract its target_type and target_path (the result is stored in the given context), and returns the start offset of the rest of the type_annotation structure (i.e. the offset to the type_index field, which is followed by num_element_value_pairs and then the name,value pairs).

Parameters:

context - information about the class being parsed. This is where the extracted target_type and target_path must be stored.

u - the start offset of a type_annotation structure.

Returns:

the start offset of the rest of the type_annotation structure.

readParameterAnnotations

private void readParameterAnnotations(MethodVisitor mv,
                                      Context context,
                                      int v,
                                      boolean visible)

Reads parameter annotations and makes the given visitor visit them.

Parameters:

mv - the visitor that must visit the annotations.

context - information about the class being parsed.

v - start offset in b of the annotations to be read.

visible - true if the annotations to be read are visible at runtime.

readAnnotationValues

private int readAnnotationValues(int v,
                                 char[] buf,
                                 boolean named,
                                 AnnotationVisitor av)

Reads the values of an annotation and makes the given visitor visit them.

Parameters:

v - the start offset in b of the values to be read (including the unsigned short that gives the number of values).

buf - buffer to be used to call readUTF8, readClass or readConst.

named - if the annotation values are named or not.

av - the visitor that must visit the values.

Returns:

the end offset of the annotation values.

readAnnotationValue

private int readAnnotationValue(int v,
                                char[] buf,
                                java.lang.String name,
                                AnnotationVisitor av)

Reads a value of an annotation and makes the given visitor visit it.

Parameters:

v - the start offset in b of the value to be read (not including the value name constant pool index).

buf - buffer to be used to call readUTF8, readClass or readConst.

name - the name of the value to be read.

av - the visitor that must visit the value.

Returns:

the end offset of the annotation value.

getImplicitFrame

private void getImplicitFrame(Context frame)

Computes the implicit frame of the method currently being parsed (as defined in the given Context) and stores it in the given context.

Parameters:

frame - information about the class being parsed.

readFrame

private int readFrame(int stackMap,
                      boolean zip,
                      boolean unzip,
                      Context frame)

Reads a stack map frame and stores the result in the given Context object.

Parameters:

stackMap - the start offset of a stack map frame in the class file.

zip - if the stack map frame at stackMap is compressed or not.

unzip - if the stack map frame must be uncompressed.

frame - where the parsed stack map frame must be stored.

Returns:

the offset of the first byte following the parsed frame.

readFrameType

private int readFrameType(java.lang.Object[] frame,
                          int index,
                          int v,
                          char[] buf,
                          Label[] labels)

Reads a stack map frame type and stores it at the given index in the given array.

Parameters:

frame - the array where the parsed type must be stored.

index - the index in 'frame' where the parsed type must be stored.

v - the start offset of the stack map frame type to read.

buf - a buffer to read strings.

labels - the labels of the method currently being parsed, indexed by their offset. If the parsed type is an Uninitialized type, a new label for the corresponding NEW instruction is stored in this array if it does not already exist.

Returns:

the offset of the first byte after the parsed type.

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].

getAttributes

private int getAttributes()

Returns the start index of the attribute_info structure of this class.

Returns:

the start index of the attribute_info structure of this class.

readAttribute

private Attribute readAttribute(Attribute[] attrs,
                                java.lang.String type,
                                int off,
                                int len,
                                char[] buf,
                                int codeOff,
                                Label[] labels)

Reads an attribute in b.

Parameters:

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 is ignored (i.e. an empty Attribute instance is returned).

type - the type of the attribute.

off - index of the first byte of the attribute's content in b. The 6 attribute header bytes, containing the type and the length of the attribute, are not taken into account here (they have already been read).

len - the length of the attribute's content.

buf - buffer to be used to call readUTF8, readClass or readConst.

codeOff - index of the first byte of code's attribute content in b, or -1 if the attribute to be read is not a code attribute. The 6 attribute header bytes, containing the type and the length of the attribute, are not taken into account here.

labels - the labels of the method's code, or null if the attribute to be read is not a code attribute.

Returns:

the attribute that has been read, or null to skip this attribute.

getItemCount

public int getItemCount()

Returns the number of constant pool items in b.

Returns:

the number of constant pool items in b.

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.

getMaxStringLength

public int getMaxStringLength()

Returns the maximum length of the strings contained in the constant pool of the class.

Returns:

the maximum length of the strings contained in the constant pool of the class.

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 java.lang.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.

readUTF

private java.lang.String readUTF(int index,
                                 int utfLen,
                                 char[] buf)

Reads UTF8 string in b.

Parameters:

index - start offset of the UTF8 string to be read.

utfLen - length of the UTF8 string to be read.

buf - 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 UTF8 string.

readClass

public java.lang.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 java.lang.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, Type or Handle corresponding to the given constant pool item.