ClassParser.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.bcel.classfile;
import java.io.BufferedInputStream;
import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.zip.ZipEntry;
import java.util.zip.ZipFile;
import org.apache.bcel.Const;
/**
* Wrapper class that parses a given Java .class file. The method <a href ="#parse">parse</a> returns a
* <a href ="JavaClass.html"> JavaClass</a> object on success. When an I/O error or an inconsistency occurs an
* appropriate exception is propagated back to the caller.
*
* The structure and the names comply, except for a few conveniences, exactly with the
* <a href="https://docs.oracle.com/javase/specs/"> JVM specification 1.0</a>. See this paper for further details about
* the structure of a bytecode file.
*/
public final class ClassParser {
private static final int BUFSIZE = 8192;
private DataInputStream dataInputStream;
private final boolean fileOwned;
private final String fileName;
private String zipFile;
private int classNameIndex;
private int superclassNameIndex;
private int major; // Compiler version
private int minor; // Compiler version
private int accessFlags; // Access rights of parsed class
private int[] interfaces; // Names of implemented interfaces
private ConstantPool constantPool; // 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 final boolean isZip; // Loaded from ZIP file
/**
* Parses class from the given stream.
*
* @param inputStream Input stream
* @param fileName File name
*/
public ClassParser(final InputStream inputStream, final String fileName) {
this.fileName = fileName;
this.fileOwned = false;
final String clazz = inputStream.getClass().getName(); // Not a very clean solution ...
this.isZip = clazz.startsWith("java.util.zip.") || clazz.startsWith("java.util.jar.");
if (inputStream instanceof DataInputStream) {
this.dataInputStream = (DataInputStream) inputStream;
} else {
this.dataInputStream = new DataInputStream(new BufferedInputStream(inputStream, BUFSIZE));
}
}
/**
* Parses class from given .class file.
*
* @param fileName file name
*/
public ClassParser(final String fileName) {
this.isZip = false;
this.fileName = fileName;
this.fileOwned = true;
}
/**
* Parses class from given .class file in a ZIP-archive
*
* @param zipFile ZIP file name
* @param fileName file name
*/
public ClassParser(final String zipFile, final String fileName) {
this.isZip = true;
this.fileOwned = true;
this.zipFile = zipFile;
this.fileName = fileName;
}
/**
* Parses the given Java class file and return an object that represents the contained data, i.e., constants, methods,
* fields and commands. A <em>ClassFormatException</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
* @throws IOException if an I/O error occurs.
* @throws ClassFormatException if a class is malformed or cannot be interpreted as a class file
*/
public JavaClass parse() throws IOException, ClassFormatException {
ZipFile zip = null;
try {
if (fileOwned) {
if (isZip) {
zip = new ZipFile(zipFile);
final ZipEntry entry = zip.getEntry(fileName);
if (entry == null) {
throw new IOException("File " + fileName + " not found");
}
dataInputStream = new DataInputStream(new BufferedInputStream(zip.getInputStream(entry), BUFSIZE));
} else {
dataInputStream = new DataInputStream(new BufferedInputStream(new FileInputStream(fileName), BUFSIZE));
}
}
/****************** 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);
// if (!(isZip && (buf.length == 1))) {
// System.err.println("WARNING: Trailing garbage at end of " + fileName);
// System.err.println(bytes + " extra bytes: " + Utility.toHexString(buf));
// }
// }
} finally {
// Read everything of interest, so close the file
if (fileOwned) {
try {
if (dataInputStream != null) {
dataInputStream.close();
}
} catch (final IOException ignored) {
// ignore close exceptions
}
}
try {
if (zip != null) {
zip.close();
}
} catch (final IOException ignored) {
// ignore close exceptions
}
}
// Return the information we have gathered in a new object
return new JavaClass(classNameIndex, superclassNameIndex, fileName, major, minor, accessFlags, constantPool, interfaces, fields, methods, attributes,
isZip ? JavaClass.ZIP : JavaClass.FILE);
}
/**
* Reads information about the attributes of the class.
*
* @throws IOException if an I/O error occurs.
* @throws ClassFormatException if a class is malformed or cannot be interpreted as a class file
*/
private void readAttributes() throws IOException, ClassFormatException {
final int attributesCount = dataInputStream.readUnsignedShort();
attributes = new Attribute[attributesCount];
for (int i = 0; i < attributesCount; i++) {
attributes[i] = Attribute.readAttribute(dataInputStream, constantPool);
}
}
/**
* Reads information about the class and its super class.
*
* @throws IOException if an I/O error occurs.
* @throws ClassFormatException if a class is malformed or cannot be interpreted as a class file
*/
private void readClassInfo() throws IOException, ClassFormatException {
accessFlags = dataInputStream.readUnsignedShort();
/*
* Interfaces are implicitly abstract, the flag should be set according to the JVM specification.
*/
if ((accessFlags & Const.ACC_INTERFACE) != 0) {
accessFlags |= Const.ACC_ABSTRACT;
}
if ((accessFlags & Const.ACC_ABSTRACT) != 0 && (accessFlags & Const.ACC_FINAL) != 0) {
throw new ClassFormatException("Class " + fileName + " can't be both final and abstract");
}
classNameIndex = dataInputStream.readUnsignedShort();
superclassNameIndex = dataInputStream.readUnsignedShort();
}
/**
* Reads constant pool entries.
*
* @throws IOException if an I/O error occurs.
* @throws ClassFormatException if a class is malformed or cannot be interpreted as a class file
*/
private void readConstantPool() throws IOException, ClassFormatException {
constantPool = new ConstantPool(dataInputStream);
}
/**
* Reads information about the fields of the class, i.e., its variables.
*
* @throws IOException if an I/O error occurs.
* @throws ClassFormatException if a class is malformed or cannot be interpreted as a class file
*/
private void readFields() throws IOException, ClassFormatException {
final int fieldsCount = dataInputStream.readUnsignedShort();
fields = new Field[fieldsCount];
for (int i = 0; i < fieldsCount; i++) {
fields[i] = new Field(dataInputStream, constantPool);
}
}
/******************** Private utility methods **********************/
/**
* Checks whether the header of the file is ok. Of course, this has to be the first action on successive file reads.
*
* @throws IOException if an I/O error occurs.
* @throws ClassFormatException if a class is malformed or cannot be interpreted as a class file
*/
private void readID() throws IOException, ClassFormatException {
if (dataInputStream.readInt() != Const.JVM_CLASSFILE_MAGIC) {
throw new ClassFormatException(fileName + " is not a Java .class file");
}
}
/**
* Reads information about the interfaces implemented by this class.
*
* @throws IOException if an I/O error occurs.
* @throws ClassFormatException if a class is malformed or cannot be interpreted as a class file
*/
private void readInterfaces() throws IOException, ClassFormatException {
final int interfacesCount = dataInputStream.readUnsignedShort();
interfaces = new int[interfacesCount];
for (int i = 0; i < interfacesCount; i++) {
interfaces[i] = dataInputStream.readUnsignedShort();
}
}
/**
* Reads information about the methods of the class.
*
* @throws IOException if an I/O error occurs.
* @throws ClassFormatException if a class is malformed or cannot be interpreted as a class file
*/
private void readMethods() throws IOException {
final int methodsCount = dataInputStream.readUnsignedShort();
methods = new Method[methodsCount];
for (int i = 0; i < methodsCount; i++) {
methods[i] = new Method(dataInputStream, constantPool);
}
}
/**
* Reads major and minor version of compiler which created the file.
*
* @throws IOException if an I/O error occurs.
* @throws ClassFormatException if a class is malformed or cannot be interpreted as a class file
*/
private void readVersion() throws IOException, ClassFormatException {
minor = dataInputStream.readUnsignedShort();
major = dataInputStream.readUnsignedShort();
}
}