Java tutorial
/**************************************************************** * 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.james.mime4j.decoder; import java.io.IOException; import java.io.InputStream; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; /** * Performs Base-64 decoding on an underlying stream. * * * @version $Id: Base64InputStream.java,v 1.3 2004/11/29 13:15:47 ntherning Exp $ */ public class Base64InputStream extends InputStream { private static Log log = LogFactory.getLog(Base64InputStream.class); private final InputStream s; private final ByteQueue byteq = new ByteQueue(3); private boolean done = false; private boolean closed = false; public Base64InputStream(InputStream s) { this.s = s; } /** * Terminates BASE64 coded content. This method does NOT close the underlying * input stream. * * @throws IOException on I/O errors. */ public void close() throws IOException { closed = true; } public int read() throws IOException { if (closed) { throw new IOException("Base64InputStream has been closed"); } if (byteq.count() == 0) { fillBuffer(); if (byteq.count() == 0) { return -1; } } byte val = byteq.dequeue(); if (val >= 0) return val; else return val & 0xFF; } /** * Retrieve data from the underlying stream, decode it, * and put the results in the byteq. * @throws IOException */ private void fillBuffer() throws IOException { byte[] data = new byte[4]; int pos = 0; int i; while (!done) { switch (i = s.read()) { case -1: if (pos > 0) { log.warn("Unexpected EOF in MIME parser, dropping " + pos + " sextets"); } return; case '=': decodeAndEnqueue(data, pos); done = true; break; default: byte sX = TRANSLATION[i]; if (sX < 0) continue; data[pos++] = sX; if (pos == data.length) { decodeAndEnqueue(data, pos); return; } break; } } } private void decodeAndEnqueue(byte[] data, int len) { int accum = 0; accum |= data[0] << 18; accum |= data[1] << 12; accum |= data[2] << 6; accum |= data[3]; byte b1 = (byte) (accum >>> 16); byteq.enqueue(b1); if (len > 2) { byte b2 = (byte) ((accum >>> 8) & 0xFF); byteq.enqueue(b2); if (len > 3) { byte b3 = (byte) (accum & 0xFF); byteq.enqueue(b3); } } } private static byte[] TRANSLATION = { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, /* 0x00 */ -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, /* 0x10 */ -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, /* 0x20 */ 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, /* 0x30 */ -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, /* 0x40 */ 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, /* 0x50 */ -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, /* 0x60 */ 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1, /* 0x70 */ -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, /* 0x80 */ -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, /* 0x90 */ -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, /* 0xA0 */ -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, /* 0xB0 */ -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, /* 0xC0 */ -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, /* 0xD0 */ -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, /* 0xE0 */ -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1 /* 0xF0 */ }; }