Package org.objectweb.asm
Class ClassReader
- java.lang.Object
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- org.objectweb.asm.ClassReader
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public class ClassReader extends Object
A parser to make aClassVisitor
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 givenClassVisitor
for each field, method and bytecode instruction encountered.- See Also:
- JVMS 4
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Field Summary
Fields Modifier and Type Field Description byte[]
b
A byte array containing the JVMS ClassFile structure to be parsed.static int
EXPAND_FRAMES
A flag to expand the stack map frames.int
header
The offset in bytes, inb
, 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 and LineNumberTable attributes.static int
SKIP_FRAMES
A flag to skip the StackMap and StackMapTable attributes.
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Constructor Summary
Constructors Constructor Description ClassReader(byte[] classFile)
Constructs a newClassReader
object.ClassReader(byte[] classFileBuffer, int classFileOffset, int classFileLength)
Constructs a newClassReader
object.ClassReader(InputStream inputStream)
Constructs a newClassReader
object.ClassReader(String className)
Constructs a newClassReader
object.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
accept(ClassVisitor classVisitor, int parsingOptions)
Makes the given visitor visit the JVMS ClassFile structure passed to the constructor of thisClassReader
.void
accept(ClassVisitor classVisitor, Attribute[] attributePrototypes, int parsingOptions)
Makes the given visitor visit the JVMS ClassFile structure passed to the constructor of thisClassReader
.int
getAccess()
Returns the class's access flags (seeOpcodes
).String
getClassName()
Returns the internal name of the class (seeType.getInternalName()
).String[]
getInterfaces()
Returns the internal names of the implemented interfaces (seeType.getInternalName()
).int
getItem(int constantPoolEntryIndex)
Returns the start offset inb
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 of name of the super class (seeType.getInternalName()
).int
readByte(int offset)
Reads a byte value inb
.String
readClass(int offset, char[] charBuffer)
Reads a CONSTANT_Class constant pool entry inb
.Object
readConst(int constantPoolEntryIndex, char[] charBuffer)
Reads a numeric or string constant pool entry inb
.int
readInt(int offset)
Reads a signed int value inb
.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 inb
.String
readModule(int offset, char[] charBuffer)
Reads a CONSTANT_Module constant pool entry inb
.String
readPackage(int offset, char[] charBuffer)
Reads a CONSTANT_Package constant pool entry inb
.short
readShort(int offset)
Reads a signed short value inb
.int
readUnsignedShort(int offset)
Reads an unsigned short value inb
.String
readUTF8(int offset, char[] charBuffer)
Reads a CONSTANT_Utf8 constant pool entry inb
.
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Field Detail
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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
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SKIP_DEBUG
public static final int SKIP_DEBUG
A flag to skip the SourceFile, SourceDebugExtension, LocalVariableTable, LocalVariableTypeTable and LineNumberTable 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.asm.Label, org.objectweb.asm.Label, int)
andMethodVisitor.visitLineNumber(int, org.objectweb.asm.Label)
are not called).- See Also:
- Constant Field Values
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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 theClassWriter.COMPUTE_FRAMES
option is used: it avoids visiting frames that will be ignored and recomputed from scratch.- See Also:
- Constant Field Values
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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
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b
public final byte[] b
A byte array containing the JVMS ClassFile structure to be parsed. The content of this array must not be modified. This field is intended forAttribute
sub classes, and is normally not needed by class visitors.NOTE: the ClassFile structure can start at any offset within this array, i.e. it does not necessarily start at offset 0. Use
getItem(int)
andheader
to get correct ClassFile element offsets within this byte array.
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header
public final int header
The offset in bytes, inb
, of the ClassFile's access_flags field.
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Constructor Detail
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ClassReader
public ClassReader(byte[] classFile)
Constructs a newClassReader
object.- Parameters:
classFile
- the JVMS ClassFile structure to be read.
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ClassReader
public ClassReader(byte[] classFileBuffer, int classFileOffset, int classFileLength)
Constructs a newClassReader
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.
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ClassReader
public ClassReader(InputStream inputStream) throws IOException
Constructs a newClassReader
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.
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ClassReader
public ClassReader(String className) throws IOException
Constructs a newClassReader
object.- Parameters:
className
- the fully qualified name of the class to be read. The ClassFile structure is retrieved with the current class loader'sClassLoader.getSystemResourceAsStream(java.lang.String)
.- Throws:
IOException
- if an exception occurs during reading.
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Method Detail
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getAccess
public int getAccess()
Returns the class's access flags (seeOpcodes
). 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[])
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getClassName
public String getClassName()
Returns the internal name of the class (seeType.getInternalName()
).- Returns:
- the internal class name.
- See Also:
ClassVisitor.visit(int, int, String, String, String, String[])
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getSuperName
public String getSuperName()
Returns the internal of name of the super class (seeType.getInternalName()
). For interfaces, the super class isObject
.- Returns:
- the internal name of the super class, or null for
Object
class. - See Also:
ClassVisitor.visit(int, int, String, String, String, String[])
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getInterfaces
public String[] getInterfaces()
Returns the internal names of the implemented interfaces (seeType.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[])
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accept
public void accept(ClassVisitor classVisitor, int parsingOptions)
Makes the given visitor visit the JVMS ClassFile structure passed to the constructor of thisClassReader
.- Parameters:
classVisitor
- the visitor that must visit this class.parsingOptions
- the options to use to parse this class. One or more ofSKIP_CODE
,SKIP_DEBUG
,SKIP_FRAMES
orEXPAND_FRAMES
.
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accept
public void accept(ClassVisitor classVisitor, Attribute[] attributePrototypes, int parsingOptions)
Makes the given visitor visit the JVMS ClassFile structure passed to the constructor of thisClassReader
.- 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 ofSKIP_CODE
,SKIP_DEBUG
,SKIP_FRAMES
orEXPAND_FRAMES
.
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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].
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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.
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getItem
public int getItem(int constantPoolEntryIndex)
Returns the start offset inb
of a JVMS 'cp_info' structure (i.e. a constant pool entry), plus one. This method is intended forAttribute
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
b
of the corresponding JVMS 'cp_info' structure, plus one.
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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.
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readByte
public int readByte(int offset)
Reads a byte value inb
. This method is intended forAttribute
sub classes, and is normally not needed by class generators or adapters.- Parameters:
offset
- the start offset of the value to be read inb
.- Returns:
- the read value.
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readUnsignedShort
public int readUnsignedShort(int offset)
Reads an unsigned short value inb
. This method is intended forAttribute
sub classes, and is normally not needed by class generators or adapters.- Parameters:
offset
- the start index of the value to be read inb
.- Returns:
- the read value.
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readShort
public short readShort(int offset)
Reads a signed short value inb
. This method is intended forAttribute
sub classes, and is normally not needed by class generators or adapters.- Parameters:
offset
- the start offset of the value to be read inb
.- Returns:
- the read value.
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readInt
public int readInt(int offset)
Reads a signed int value inb
. This method is intended forAttribute
sub classes, and is normally not needed by class generators or adapters.- Parameters:
offset
- the start offset of the value to be read inb
.- Returns:
- the read value.
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readLong
public long readLong(int offset)
Reads a signed long value inb
. This method is intended forAttribute
sub classes, and is normally not needed by class generators or adapters.- Parameters:
offset
- the start offset of the value to be read inb
.- Returns:
- the read value.
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readUTF8
public String readUTF8(int offset, char[] charBuffer)
Reads a CONSTANT_Utf8 constant pool entry inb
. This method is intended forAttribute
sub classes, and is normally not needed by class generators or adapters.- Parameters:
offset
- the start offset of an unsigned short value inb
, 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.
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readClass
public String readClass(int offset, char[] charBuffer)
Reads a CONSTANT_Class constant pool entry inb
. This method is intended forAttribute
sub classes, and is normally not needed by class generators or adapters.- Parameters:
offset
- the start offset of an unsigned short value inb
, 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.
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readModule
public String readModule(int offset, char[] charBuffer)
Reads a CONSTANT_Module constant pool entry inb
. This method is intended forAttribute
sub classes, and is normally not needed by class generators or adapters.- Parameters:
offset
- the start offset of an unsigned short value inb
, 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.
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readPackage
public String readPackage(int offset, char[] charBuffer)
Reads a CONSTANT_Package constant pool entry inb
. This method is intended forAttribute
sub classes, and is normally not needed by class generators or adapters.- Parameters:
offset
- the start offset of an unsigned short value inb
, 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.
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readConst
public Object readConst(int constantPoolEntryIndex, char[] charBuffer)
Reads a numeric or string constant pool entry inb
. This method is intended forAttribute
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
orConstantDynamic
corresponding to the specified constant pool entry.
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