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/*
* 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 org.apache.tomcat.util.bcel.Const;
/**
* Wrapper class that parses a given Java .class file. The method parse returns a
* JavaClass 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
* JVM specification 1.0. See this paper for
* further details about the structure of a bytecode file.
*/
public final class ClassParser {
private static final int MAGIC = 0xCAFEBABE;
private final DataInput dataInputStream;
private String class_name, superclass_name;
private int access_flags; // Access rights of parsed class
private String[] interface_names; // Names of implemented interfaces
private ConstantPool constant_pool; // collection of constants
private Annotations runtimeVisibleAnnotations; // "RuntimeVisibleAnnotations" attribute defined in the class
private static final int BUFSIZE = 8192;
private static final String[] INTERFACES_EMPTY_ARRAY = new String[0];
/**
* Parse class from the given stream.
*
* @param inputStream Input stream
*/
public ClassParser(final InputStream inputStream) {
this.dataInputStream = new DataInputStream(new BufferedInputStream(inputStream, BUFSIZE));
}
/**
* Parse the given Java class file and return an object that represents
* the contained data, i.e., constants, methods, fields and commands.
* A ClassFormatException 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 occurs reading the byte code
* @throws ClassFormatException If the byte code is invalid
*/
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();
// Return the information we have gathered in a new object
return new JavaClass(class_name, superclass_name,
access_flags, constant_pool, interface_names,
runtimeVisibleAnnotations);
}
/**
* Read information about the attributes of the class.
* @throws IOException
* @throws ClassFormatException
*/
private void readAttributes() throws IOException, ClassFormatException {
final int attributes_count = dataInputStream.readUnsignedShort();
for (int i = 0; i < attributes_count; 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) constant_pool.getConstant(name_index,
Const.CONSTANT_Utf8);
name = c.getBytes();
// Length of data in bytes
length = dataInputStream.readInt();
if (name.equals("RuntimeVisibleAnnotations")) {
if (runtimeVisibleAnnotations != null) {
throw new ClassFormatException(
"RuntimeVisibleAnnotations attribute is not allowed more than once in a class file");
}
runtimeVisibleAnnotations = new Annotations(dataInputStream, constant_pool);
} else {
// All other attributes are skipped
Utility.skipFully(dataInputStream, length);
}
}
}
/**
* Read information about the class and its super class.
* @throws IOException
* @throws ClassFormatException
*/
private void readClassInfo() throws IOException, ClassFormatException {
access_flags = dataInputStream.readUnsignedShort();
/* Interfaces are implicitely abstract, the flag should be set
* according to the JVM specification.
*/
if ((access_flags & Const.ACC_INTERFACE) != 0) {
access_flags |= Const.ACC_ABSTRACT;
}
if (((access_flags & Const.ACC_ABSTRACT) != 0)
&& ((access_flags & Const.ACC_FINAL) != 0)) {
throw new ClassFormatException("Class can't be both final and abstract");
}
int class_name_index = dataInputStream.readUnsignedShort();
class_name = Utility.getClassName(constant_pool, class_name_index);
int superclass_name_index = dataInputStream.readUnsignedShort();
if (superclass_name_index > 0) {
// May be zero -> class is java.lang.Object
superclass_name = Utility.getClassName(constant_pool, superclass_name_index);
} else {
superclass_name = "java.lang.Object";
}
}
/**
* Read constant pool entries.
* @throws IOException
* @throws ClassFormatException
*/
private void readConstantPool() throws IOException, ClassFormatException {
constant_pool = new ConstantPool(dataInputStream);
}
/**
* Read information about the fields of the class, i.e., its variables.
* @throws IOException
* @throws ClassFormatException
*/
private void readFields() throws IOException, ClassFormatException {
final int fields_count = dataInputStream.readUnsignedShort();
for (int i = 0; i < fields_count; i++) {
Utility.swallowFieldOrMethod(dataInputStream);
}
}
/******************** 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.
* @throws IOException
* @throws ClassFormatException
*/
private void readID() throws IOException, ClassFormatException {
if (dataInputStream.readInt() != MAGIC) {
throw new ClassFormatException("It is not a Java .class file");
}
}
/**
* Read information about the interfaces implemented by this class.
* @throws IOException
* @throws ClassFormatException
*/
private void readInterfaces() throws IOException, ClassFormatException {
final int interfaces_count = dataInputStream.readUnsignedShort();
if (interfaces_count > 0) {
interface_names = new String[interfaces_count];
for (int i = 0; i < interfaces_count; i++) {
int index = dataInputStream.readUnsignedShort();
interface_names[i] = Utility.getClassName(constant_pool, index);
}
} else {
interface_names = INTERFACES_EMPTY_ARRAY;
}
}
/**
* Read information about the methods of the class.
* @throws IOException
* @throws ClassFormatException
*/
private void readMethods() throws IOException, ClassFormatException {
final int methods_count = dataInputStream.readUnsignedShort();
for (int i = 0; i < methods_count; i++) {
Utility.swallowFieldOrMethod(dataInputStream);
}
}
/**
* Read major and minor version of compiler which created the file.
* @throws IOException
* @throws ClassFormatException
*/
private void readVersion() throws IOException, ClassFormatException {
// file.readUnsignedShort(); // Unused minor
// file.readUnsignedShort(); // Unused major
Utility.skipFully(dataInputStream, 4);
}
}
