UTF8Constant.java

/*******************************************************************************
 * Copyright (c) 1998, 2015 Oracle and/or its affiliates. All rights reserved.
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0
 * which accompanies this distribution.
 * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
 * and the Eclipse Distribution License is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *     Oracle - initial API and implementation from Oracle TopLink
******************************************************************************/
package org.eclipse.persistence.tools.workbench.utility.classfile;

import java.io.IOException;

import org.eclipse.persistence.tools.workbench.utility.classfile.tools.ClassFileDataInputStream;
import org.eclipse.persistence.tools.workbench.utility.io.IndentingPrintWriter;


/**
 * This class models a class file UTF8 constant:
 *     u1 tag;
 *     u2 length;
 *     u1[] bytes;
 *
 * See "The Java Virtual Machine Specification" Chapter 4.
 */
public class UTF8Constant extends Constant {
    private String value;

    /**
     * Construct a class file constant from the specified stream
     * of byte codes.
     */
    UTF8Constant(ConstantPool pool, byte tag, ClassFileDataInputStream stream) throws IOException {
        super(pool, tag, stream);
    }

    void initialize(ClassFileDataInputStream stream) throws IOException {
        this.value = this.readStringFrom(stream);
    }

    private String readStringFrom(ClassFileDataInputStream stream) throws IOException {
        short len = stream.readU2();
        StringBuffer sb = new StringBuffer(len);
        for (short count = 0; count < len; count++) {
            byte b = stream.readU1();
            if ((b & 0x80) == 0) {
                // if the first bit is 0, we have a single-byte character
                sb.append((char) b);
            } else {
                // if the first bit is 1, we have a multi-byte character
                if ((b & 0x40) == 0) {
                    // if the second bit is 0 at this point, something is wrong...
                    throw this.badByte(b);
                }
                short s;
                if ((b & 0x20) == 0) {
                    // if the third bit is 0, we have a 2-byte character
                    s = (short) ((b & 0x1F) << 6);        // bits 4-0 become bits 10-6
                } else {
                    // if the third bit is 1, we have a 3-byte character
                    s = (short) ((b & 0x0F) << 12);        // bits 3-0 become bits 15-12
                    b = stream.readU1();
                    this.checkContinuation(b);
                    count++;
                    s |= ((b & 0x3f) << 6);        // bits 5-0 become bits 11-6
                }
                b = stream.readU1();
                this.checkContinuation(b);
                count++;
                s |= (b & 0x3f);        // bits 5-0 become bits 5-0
                sb.append((char) s);
            }
        }
        return sb.toString();
    }

    private final IOException badByte(byte b) {
        return new IOException("Invalid UTF-8 byte: " + Byte.toString(b));
    }

    private final void checkContinuation(byte b) throws IOException {
        // the first bit must be 1, the second bit must be 0
        if (((b & 0x80) == 0) || ((b & 0x40) != 0)) {
            throw this.badByte(b);
        }
    }

    public void displayStringOn(IndentingPrintWriter writer) {
        super.displayStringOn(writer);
        writer.print(" value: \"");
        writer.print(this.value);
        writer.println("\"");
    }

    public String description() {
        return "UTF8";
    }

    public String string() {
        return this.value;
    }

    public Object value() {
        return this.value;
    }

    public void accept(Visitor visitor) {
        visitor.visit(this);
    }

}