Package com.googlecode.aviator.asm

Class ClassReader

java.lang.Object
com.googlecode.aviator.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.

  • Field Details

    • SIGNATURES

      static final boolean SIGNATURES
      True to enable signatures support.
      See Also:

    • ANNOTATIONS

      static final boolean ANNOTATIONS
      True to enable annotations support.
      See Also:

    • FRAMES

      static final boolean FRAMES
      True to enable stack map frames support.
      See Also:

    • WRITER

      static final boolean WRITER
      True to enable bytecode writing support.
      See Also:

    • RESIZE

      static final boolean RESIZE
      True to enable JSR_W and GOTO_W support.
      See Also:

    • 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:

    • 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:

    • 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:

    • 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:

    • 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 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.

  • Constructor Details

    • 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 binary qualified name of the class to be read.
      Throws:
      IOException - if an exception occurs during reading.

  • Method Details

    • 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:

    • getClassName

      public String getClassName()
      Returns the internal name of the class (see getInternalName).
      Returns:
      the internal class name
      See Also:

    • 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:

    • 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:

    • 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(InputStream is, boolean close) throws 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:
      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.

    • readParameterAnnotations

      private void readParameterAnnotations(int v, String desc, char[] buf, boolean visible, MethodVisitor mv)
      Reads parameter annotations and makes the given visitor visit them.
      Parameters:
      v - start offset in b of the annotations to be read.
      desc - the method descriptor.
      buf - buffer to be used to call readUTF8, readClass or readConst.
      visible - true if the annotations to be read are visible at runtime.
      mv - the visitor that must visit the annotations.

    • 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, 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, Label[] labels, 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.
      labels - the labels of the method currently being parsed, indexed by their offset. A new label for the parsed stack map frame is stored in this array if it does not already exist.
      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(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, 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 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 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 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, Type or Handle corresponding to the given constant pool item.