Java tutorial
package org.aspectj.apache.bcel.classfile; /* ==================================================================== * The Apache Software License, Version 1.1 * * Copyright (c) 2001 The Apache Software Foundation. All rights * reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * * 3. 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Products derived from this software may not be called "Apache", * "Apache BCEL", nor may "Apache" appear in their name, without * prior written permission of the Apache Software Foundation. * * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE * DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * ==================================================================== * * This software consists of voluntary contributions made by many * individuals on behalf of the Apache Software Foundation. For more * information on the Apache Software Foundation, please see * <http://www.apache.org/>. */ import java.io.DataInputStream; import java.io.DataOutputStream; import java.io.IOException; import org.aspectj.apache.bcel.Constants; /** * This class represents a chunk of Java byte code contained in a method. It is instantiated by the * <em>Attribute.readAttribute()</em> method. A <em>Code</em> attribute contains informations about operand stack, local variables, * byte code and the exceptions handled within this method. * * This attribute has attributes itself, namely <em>LineNumberTable</em> which is used for debugging purposes and * <em>LocalVariableTable</em> which contains information about the local variables. * * @version $Id: Code.java,v 1.9 2009/10/05 17:35:36 aclement Exp $ * @author <A HREF="mailto:markus.dahm@berlin.de">M. Dahm</A> * @see Attribute * @see CodeException * @see LineNumberTable * @see LocalVariableTable */ public final class Code extends Attribute { private int maxStack; // Maximum size of stack used by this method private int maxLocals; // Number of local variables private byte[] code; // Actual byte code private CodeException[] exceptionTable; private Attribute[] attributes; private static final CodeException[] NO_EXCEPTIONS = new CodeException[] {}; /** * Initialize from another object. Note that both objects use the same references (shallow copy). Use copy() for a physical * copy. */ public Code(Code c) { this(c.getNameIndex(), c.getLength(), c.getMaxStack(), c.getMaxLocals(), c.getCode(), c.getExceptionTable(), c.getAttributes(), c.getConstantPool()); } Code(int name_index, int length, DataInputStream file, ConstantPool constant_pool) throws IOException { // Initialize with some default values which will be overwritten later this(name_index, length, file.readUnsignedShort(), file.readUnsignedShort(), (byte[]) null, (CodeException[]) null, (Attribute[]) null, constant_pool); int len = file.readInt(); code = new byte[len]; // Read byte code file.readFully(code); /* * Read exception table that contains all regions where an exception handler is active, i.e., a try { ... } catch() block. */ len = file.readUnsignedShort(); if (len == 0) { exceptionTable = NO_EXCEPTIONS; } else { exceptionTable = new CodeException[len]; for (int i = 0; i < len; i++) { exceptionTable[i] = new CodeException(file); } } // Read all attributes, eg: LineNumberTable, LocalVariableTable attributes = AttributeUtils.readAttributes(file, constant_pool); /* * Adjust length, because of setAttributes in this(), s.b. length is incorrect, because it didn't take the internal * attributes into account yet! Very subtle bug, fixed in 3.1.1. */ this.length = length; } /** * @param name_index Index pointing to the name <em>Code</em> * @param length Content length in bytes * @param max_stack Maximum size of stack * @param max_locals Number of local variables * @param code Actual byte code * @param exception_table Table of handled exceptions * @param attributes Attributes of code: LineNumber or LocalVariable * @param constant_pool Array of constants */ public Code(int name_index, int length, int max_stack, int max_locals, byte[] code, CodeException[] exception_table, Attribute[] attributes, ConstantPool constant_pool) { super(Constants.ATTR_CODE, name_index, length, constant_pool); this.maxStack = max_stack; this.maxLocals = max_locals; setCode(code); setExceptionTable(exception_table); setAttributes(attributes); // Overwrites length! } /** * Called by objects that are traversing the nodes of the tree implicitely defined by the contents of a Java class. I.e., the * hierarchy of methods, fields, attributes, etc. spawns a tree of objects. * * @param v Visitor object */ @Override public void accept(ClassVisitor v) { v.visitCode(this); } /** * Dump code attribute to file stream in binary format. * * @param file Output file stream * @throws IOException */ @Override public final void dump(DataOutputStream file) throws IOException { super.dump(file); file.writeShort(maxStack); file.writeShort(maxLocals); file.writeInt(code.length); file.write(code, 0, code.length); file.writeShort(exceptionTable.length); for (int i = 0; i < exceptionTable.length; i++) { exceptionTable[i].dump(file); } file.writeShort(attributes.length); for (int i = 0; i < attributes.length; i++) { attributes[i].dump(file); } } /** * @return Collection of code attributes. * @see Attribute */ public final Attribute[] getAttributes() { return attributes; } /** * @return LineNumberTable of Code, if it has one */ public LineNumberTable getLineNumberTable() { for (int i = 0; i < attributes.length; i++) { if (attributes[i].tag == Constants.ATTR_LINE_NUMBER_TABLE) { return (LineNumberTable) attributes[i]; } } return null; } /** * @return LocalVariableTable of Code, if it has one */ public LocalVariableTable getLocalVariableTable() { for (int i = 0; i < attributes.length; i++) { if (attributes[i].tag == Constants.ATTR_LOCAL_VARIABLE_TABLE) { return (LocalVariableTable) attributes[i]; } } return null; } /** * @return Actual byte code of the method. */ public final byte[] getCode() { return code; } /** * @return Table of handled exceptions. * @see CodeException */ public final CodeException[] getExceptionTable() { return exceptionTable; } /** * @return Number of local variables. */ public final int getMaxLocals() { return maxLocals; } /** * @return Maximum size of stack used by this method. */ public final int getMaxStack() { return maxStack; } /** * @return the internal length of this code attribute (minus the first 6 bytes) and excluding all its attributes */ private final int getInternalLength() { return 2 /* max_stack */ + 2 /* max_locals */ + 4 /* code length */ + (code == null ? 0 : code.length) /* byte-code */ + 2 /* exception-table length */ + 8 * (exceptionTable == null ? 0 : exceptionTable.length) /* exception table */ + 2 /* attributes count */; } /** * @return the full size of this code attribute, minus its first 6 bytes, including the size of all its contained attributes */ private final int calculateLength() { int len = 0; if (attributes != null) { for (int i = 0; i < attributes.length; i++) { len += attributes[i].length + 6 /* attribute header size */; } } return len + getInternalLength(); } /** * @param attributes. */ public final void setAttributes(Attribute[] attributes) { this.attributes = attributes; length = calculateLength(); // Adjust length } /** * @param code byte code */ public final void setCode(byte[] code) { this.code = code; } /** * @param exception_table exception table */ public final void setExceptionTable(CodeException[] exception_table) { this.exceptionTable = exception_table; } /** * @param max_locals maximum number of local variables */ public final void setMaxLocals(int max_locals) { this.maxLocals = max_locals; } /** * @param max_stack maximum stack size */ public final void setMaxStack(int max_stack) { this.maxStack = max_stack; } /** * @return String representation of code chunk. */ public final String toString(boolean verbose) { StringBuffer buf; buf = new StringBuffer("Code(max_stack = " + maxStack + ", max_locals = " + maxLocals + ", code_length = " + code.length + ")\n" + Utility.codeToString(code, cpool, 0, -1, verbose)); if (exceptionTable.length > 0) { buf.append("\nException handler(s) = \n" + "From\tTo\tHandler\tType\n"); for (int i = 0; i < exceptionTable.length; i++) { buf.append(exceptionTable[i].toString(cpool, verbose) + "\n"); } } if (attributes.length > 0) { buf.append("\nAttribute(s) = \n"); for (int i = 0; i < attributes.length; i++) { buf.append(attributes[i].toString() + "\n"); } } return buf.toString(); } /** * @return String representation of code chunk. */ @Override public final String toString() { return toString(true); } // /** // * @return deep copy of this attribute // */ // public Attribute copy(ConstantPool constant_pool) { // Code c = (Code)clone(); // c.code = (byte[])code.clone(); // c.cpool = constant_pool; // // c.exceptionTable = new CodeException[exceptionTable.length]; // for(int i=0; i < exceptionTable.length; i++) // c.exceptionTable[i] = exceptionTable[i].copy(); // // c.attributes = new Attribute[attributes.length]; // for(int i=0; i < attributes.length; i++) // c.attributes[i] = attributes[i].copy(constant_pool); // // return c; // } /** * Returns the same as toString(true) except that the attribute information isn't included (line numbers). Can be used to check * whether two pieces of code are equivalent. */ public String getCodeString() { StringBuffer codeString = new StringBuffer(); codeString.append("Code(max_stack = ").append(maxStack); codeString.append(", max_locals = ").append(maxLocals); codeString.append(", code_length = ").append(code.length).append(")\n"); codeString.append(Utility.codeToString(code, cpool, 0, -1, true)); if (exceptionTable.length > 0) { codeString.append("\n").append("Exception entries = ").append(exceptionTable.length).append("\n"); for (int i = 0; i < exceptionTable.length; i++) { CodeException exc = exceptionTable[i]; int type = exc.getCatchType(); String name = "finally"; if (type != 0) { name = this.cpool.getConstantString(type, Constants.CONSTANT_Class); } codeString.append(name).append("["); codeString.append(exc.getStartPC()).append(">").append(exc.getEndPC()).append("]\n"); } } return codeString.toString(); } }