org.springframework.asm

## Class ClassReader

- java.lang.Object
- - org.springframework.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

    All Methods Instance Methods Concrete Methods
    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`.
    `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.springframework.asm.Label, org.springframework.asm.Label, int)`, `MethodVisitor.visitLineNumber(int, org.springframework.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`.

    - #### 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.