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ClassParser.java

package de.fub.bytecode.classfile;

import  de.fub.bytecode.Constants;
import  java.io.*;
import  java.util.zip.*;

/**
 * Wrapper class that parses a given Java .class file. The method
 * <A href ="#parse">parse</A> returns a
 * <A href ="de.fub.bytecode.classfile.JavaClass.html">
 * JavaClass</A> object on success. When an I/O error or an
 * inconsistency occurs an appropiate exception is propagated back
 * to the caller.
 *
 * The structure and the names comply, except for a few conveniences,
 * exactly with the <A href="ftp://java.sun.com/docs/specs/vmspec.ps">
 * JVM specification 1.0</a>. See this paper for
 * further details about the structure of a bytecode file.
 *
 * @version $Id: ClassParser.java,v 1.1.1.1 2002/01/24 03:44:00 pserver Exp $
 * @author  <A HREF="http://www.inf.fu-berlin.de/~dahm">M. Dahm</A>
 */
public final class ClassParser implements Constants {
  private DataInputStream file;
  private ZipFile         zip;
  private String          file_name;
  private int             class_name_index, superclass_name_index;
  private int             major, minor; // Compiler version
  private int             access_flags; // Access rights of parsed class
  private int[]           interfaces; // Names of implemented interfaces
  private ConstantPool    constant_pool; // collection of constants
  private Field[]         fields; // class fields, i.e. its variables
  private Method[]        methods; // methods defined in the class
  private Attribute[]     attributes; // attributes defined in the class

  private static final int BUFSIZE = 8192;

  /**
   * Parse class from the given stream.
   *
   * @param file Input stream
   * @param file_name File name
   */
  public ClassParser(InputStream file, String file_name) {
    this.file_name = file_name;

    if(file instanceof DataInputStream) // Is already a data stream
      this.file = (DataInputStream)file;
    else
      this.file = new DataInputStream(new BufferedInputStream(file, BUFSIZE));
  }  
  /** Parse class from given .class file.
   *
   * @param file_name file name
   * @throw IOException
   */
  public ClassParser(String file_name) throws IOException
  {    
    this.file_name = file_name;
    file = new DataInputStream(new BufferedInputStream
                   (new FileInputStream(file_name), BUFSIZE));
  }  
  /** Parse class from given .class file in a ZIP-archive
   *
   * @param file_name file name
   * @throw IOException
   */
  public ClassParser(String zip_file, String file_name) throws IOException
  {    
    zip = new ZipFile(zip_file);
    ZipEntry entry = zip.getEntry(file_name);
           
    this.file_name = file_name;

    file = new DataInputStream(new BufferedInputStream(zip.getInputStream(entry),
                               BUFSIZE));
  }  
  /**
   * Parse the given Java class file and return an object that represents
   * the contained data, i.e. constants, methods, fields and commands.
   * A <em>ClassFormatError</em> is raised, if the file is not a valid
   * .class file. (This does not include verification of the byte code as it
   * is performed by the java interpreter).
   *
   * @return Class object representing the parsed class file
   * @throw  IOException
   * @throw  ClassFormatError
   */  
  public JavaClass parse() throws IOException, ClassFormatError
  {
    /****************** Read headers ********************************/
    // Check magic tag of class file
    readID();

    // Get compiler version
    readVersion();

    /****************** Read constant pool and related **************/
    // Read constant pool entries
    readConstantPool();
    
    // Get class information
    readClassInfo();

    // Get interface information, i.e. implemented interfaces
    readInterfaces();

    /****************** Read class fields and methods ***************/ 
    // Read class fields, i.e. the variables of the class
    readFields();

    // Read class methods, i.e. the functions in the class
    readMethods();

    // Read class attributes
    readAttributes();

    // Check for unknown variables
    //Unknown[] u = Unknown.getUnknownAttributes();
    //for(int i=0; i < u.length; i++)
    //  System.err.println("WARNING: " + u[i]);

    // Everything should have been read now
    if(file.available() > 0) {
      int bytes = file.available();
      byte[] buf = new byte[bytes];
      file.read(buf);

//      System.err.println("WARNING: Trailing garbage at end of " + file_name);
//      System.err.println(bytes + " extra bytes: " + Utility.toHexString(buf));
    }

    // Read everything of interest, so close the file
    file.close();
    if(zip != null)
      zip.close();

    // Return the information we have gathered in a new object
    return new JavaClass(class_name_index, superclass_name_index, 
             file_name, major, minor, access_flags,
             constant_pool, interfaces, fields,
             methods, attributes);
  }  
  /**
   * Read information about the attributes of the attributes of the class.
   * @throw  IOException
   * @throw  ClassFormatError
   */
  private final void readAttributes() throws IOException, ClassFormatError
  {
    int attributes_count;

    attributes_count = file.readUnsignedShort();
    attributes       = new Attribute[attributes_count];

    for(int i=0; i < attributes_count; i++)
      attributes[i] = Attribute.readAttribute(file, constant_pool);
  }  
  /**
   * Read information about the class and its super class.
   * @throw  IOException
   * @throw  ClassFormatError
   */
  private final void readClassInfo() throws IOException, ClassFormatError
  {
    access_flags = file.readUnsignedShort();

    /* Interfaces are implicitely abstract, the flag should be set
     * according to the JVM specification.
     */
    if((access_flags & ACC_INTERFACE) != 0)
      access_flags |= ACC_ABSTRACT;

    if(((access_flags & ACC_ABSTRACT) != 0) && 
       ((access_flags & ACC_FINAL)    != 0 ))
      throw new ClassFormatError("Class can't be both final and abstract");

    class_name_index      = file.readUnsignedShort();
    superclass_name_index = file.readUnsignedShort();
  }  
  /**
   * Read constant pool entries.
   * @throw  IOException
   * @throw  ClassFormatError
   */
  private final void readConstantPool() throws IOException, ClassFormatError
  {
    constant_pool = new ConstantPool(file);
  }  
  /**
   * Read information about the fields of the class, i.e. its variables.
   * @throw  IOException
   * @throw  ClassFormatError
   */
  private final void readFields() throws IOException, ClassFormatError
  {
    int fields_count;

    fields_count = file.readUnsignedShort();
    fields       = new Field[fields_count];

    for(int i=0; i < fields_count; i++)
      fields[i] = new Field(file, constant_pool);
  }  
  // No getXXX/setXXX methods, wouldn't make too much sense

  /******************** Private utility methods **********************/

  /**
   * Check whether the header of the file is ok.
   * Of course, this has to be the first action on successive file reads.
   * @throw  IOException
   * @throw  ClassFormatError
   */
  private final void readID() throws IOException, ClassFormatError
  {
    int magic = 0xCAFEBABE;

    if(file.readInt() != magic)
      throw new ClassFormatError(file_name + " is not a Java .class file");
  }  
  /**
   * Read information about the interfaces implemented by this class.
   * @throw  IOException
   * @throw  ClassFormatError
   */
  private final void readInterfaces() throws IOException, ClassFormatError
  {
    int interfaces_count;

    interfaces_count = file.readUnsignedShort();
    interfaces       = new int[interfaces_count];

    for(int i=0; i < interfaces_count; i++)
      interfaces[i] = file.readUnsignedShort();
  }  
  /**
   * Read information about the methods of the class.
   * @throw  IOException
   * @throw  ClassFormatError
   */
  private final void readMethods() throws IOException, ClassFormatError
  {
    int methods_count;

    methods_count = file.readUnsignedShort();
    methods       = new Method[methods_count];

    for(int i=0; i < methods_count; i++)
      methods[i] = new Method(file, constant_pool);
  }  
  /**
   * Read major and minor version of compiler which created the file.
   * @throw  IOException
   * @throw  ClassFormatError
   */
  private final void readVersion() throws IOException, ClassFormatError
  {
    minor = file.readUnsignedShort();
    major = file.readUnsignedShort();

    if(!((major == MAJOR_1_1) && (minor == MINOR_1_1)) &&
       !((major == MAJOR_1_2) && (minor >= MINOR_1_2)))
      System.err.println("Possibly incompatible version: " + major + "." + minor);
  }  
}

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