Class ClassReader


  • public final 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.
    • Field Summary

      Fields 
      Modifier and Type Field 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.
    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void accept​(ClassVisitor classVisitor, int flags)
      Makes the given visitor visit the Java class of this ClassReader .
      void accept​(ClassVisitor classVisitor, Attribute[] attrs, 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.
      java.lang.String readClass​(int index, char[] buf)
      Reads a class constant pool item in b.
      private static byte[] readClass​(java.io.InputStream is, boolean close)
      Reads the bytecode of a class.
      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

      • 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.