/*
* 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.tomcat.util.bcel.classfile;
import java.io.BufferedInputStream;
import java.io.DataInput;
import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
import org.apache.tomcat.util.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 final DataInput dataInputStream;
private String className;
private String superclassName;
private int accessFlags; // Access rights of parsed class
private String[] interfaceNames; // Names of implemented interfaces
private ConstantPool constantPool; // collection of constants
private Annotations runtimeVisibleAnnotations; // "RuntimeVisibleAnnotations" attribute defined in the class
private List<Annotations> runtimeVisibleFieldOrMethodAnnotations; // "RuntimeVisibleAnnotations" attribute defined elsewhere
private static final String[] INTERFACES_EMPTY_ARRAY = {};
/**
* Parses class from the given stream.
*
* @param inputStream Input stream
*/
public ClassParser(final InputStream inputStream) {
this.dataInputStream = new DataInputStream(new BufferedInputStream(inputStream, BUFSIZE));
}
/**
* 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 {
//****************** 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(false);
// Return the information we have gathered in a new object
return new JavaClass(className, superclassName, accessFlags, constantPool, interfaceNames,
runtimeVisibleAnnotations, runtimeVisibleFieldOrMethodAnnotations);
}
/**
* Reads information about the attributes of the class.
* @param fieldOrMethod false if processing a 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(boolean fieldOrMethod) throws IOException, ClassFormatException {
final int attributesCount = dataInputStream.readUnsignedShort();
for (int i = 0; i < attributesCount; i++) {
ConstantUtf8 c;
String name;
int name_index;
int length;
// Get class name from constant pool via 'name_index' indirection
name_index = dataInputStream.readUnsignedShort();
c = (ConstantUtf8) constantPool.getConstant(name_index,
Const.CONSTANT_Utf8);
name = c.getBytes();
// Length of data in bytes
length = dataInputStream.readInt();
if (name.equals("RuntimeVisibleAnnotations")) {
if (fieldOrMethod) {
Annotations fieldOrMethodAnnotations = new Annotations(dataInputStream, constantPool);
if (runtimeVisibleFieldOrMethodAnnotations == null) {
runtimeVisibleFieldOrMethodAnnotations = new ArrayList<>();
}
runtimeVisibleFieldOrMethodAnnotations.add(fieldOrMethodAnnotations);
} else {
if (runtimeVisibleAnnotations != null) {
throw new ClassFormatException(
"RuntimeVisibleAnnotations attribute is not allowed more than once in a class file");
}
runtimeVisibleAnnotations = new Annotations(dataInputStream, constantPool);
}
} else {
// All other attributes are skipped
Utility.skipFully(dataInputStream, length);
}
}
}
/**
* 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 can't be both final and abstract");
}
int classNameIndex = dataInputStream.readUnsignedShort();
className = Utility.getClassName(constantPool, classNameIndex);
int superclass_name_index = dataInputStream.readUnsignedShort();
if (superclass_name_index > 0) {
// May be zero -> class is java.lang.Object
superclassName = Utility.getClassName(constantPool, superclass_name_index);
} else {
superclassName = "java.lang.Object";
}
}
/**
* 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();
for (int i = 0; i < fieldsCount; i++) {
// file.readUnsignedShort(); // Unused access flags
// file.readUnsignedShort(); // name index
// file.readUnsignedShort(); // signature index
Utility.skipFully(dataInputStream, 6);
readAttributes(true);
}
}
/**
* 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("It 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();
if (interfacesCount > 0) {
interfaceNames = new String[interfacesCount];
for (int i = 0; i < interfacesCount; i++) {
int index = dataInputStream.readUnsignedShort();
interfaceNames[i] = Utility.getClassName(constantPool, index);
}
} else {
interfaceNames = INTERFACES_EMPTY_ARRAY;
}
}
/**
* 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, ClassFormatException {
final int methodsCount = dataInputStream.readUnsignedShort();
for (int i = 0; i < methodsCount; i++) {
// file.readUnsignedShort(); // Unused access flags
// file.readUnsignedShort(); // name index
// file.readUnsignedShort(); // signature index
Utility.skipFully(dataInputStream, 6);
readAttributes(true);
}
}
/**
* 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 {
// file.readUnsignedShort(); // Unused minor
// file.readUnsignedShort(); // Unused major
Utility.skipFully(dataInputStream, 4);
}
}