检查文本流，并判断该文本应使用哪种编码类型。
/* * 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 com.nowjava; import java.io.BufferedInputStream;/*NowJava.com 提供*/ import java.io.InputStream; import java.io.IOException; public class Main { /** * Examine a stream of text and make a judgement on what encoding * type should be used for the text. Ideally, we want to use 7bit * encoding to determine this, but we may need to use either quoted-printable * or base64. The choice is made on the ratio of 7-bit characters to non-7bit. * * @param content An input stream for the content we're examining. * * @exception IOException */ public static String getTextTransferEncoding(InputStream content) throws IOException { // for efficiency, we'll read in blocks. BufferedInputStream in = new BufferedInputStream(content, 4096); int span = 0; // span of characters without a line break. boolean containsLongLines = false; int asciiChars = 0; int nonAsciiChars = 0; while (true) {//from n o w j a v a . c o m - 时代Java int ch = in.read(); // if we hit an EOF here, go decide what type we've actually found. if (ch == -1) { break; } // we found a linebreak. Reset the line length counters on either one. We don't // really need to validate here. if (ch == '\n' || ch == '\r') { // hit a line end, reset our line length counter span = 0; } else { span++; // the text has long lines, we can't transfer this as unencoded text. if (span > 998) { containsLongLines = true; } // non-ascii character, we have to transfer this in binary. if (!isAscii(ch)) { nonAsciiChars++; } else { asciiChars++; } } } // looking good so far, only valid chars here. if (nonAsciiChars == 0) { // does this contain long text lines? We need to use a Q-P encoding which will // be only slightly longer, but handles folding the longer lines. if (containsLongLines) { return "quoted-printable"; } else { // ideal! Easiest one to handle. return "7bit"; } } else { // mostly characters requiring encoding? Base64 is our best bet. if (nonAsciiChars > asciiChars) { return "base64"; } else { // Q-P encoding will use fewer bytes than the full Base64. return "quoted-printable"; } } } /** * Examine a stream of text and make a judgement on what encoding * type should be used for the text. Ideally, we want to use 7bit * encoding to determine this, but we may need to use either quoted-printable * or base64. The choice is made on the ratio of 7-bit characters to non-7bit. * * @param content A string for the content we're examining. */ public static String getTextTransferEncoding(String content) { int asciiChars = 0; int nonAsciiChars = 0; for (int i = 0; i < content.length(); i++) { int ch = content.charAt(i); // non-ascii character, we have to transfer this in binary. if (!isAscii(ch)) { nonAsciiChars++; } else { asciiChars++; } } // looking good so far, only valid chars here. if (nonAsciiChars == 0) { // ideal! Easiest one to handle. return "7bit"; } else { // mostly characters requiring encoding? Base64 is our best bet. if (nonAsciiChars > asciiChars) { return "base64"; } else { // Q-P encoding will use fewer bytes than the full Base64. return "quoted-printable"; } } } /** * Test to see if this string contains only US-ASCII (i.e., 7-bit * ASCII) Characters. * * @param s The test string. * * @return true if this is a valid 7-bit ASCII encoding, false if it * contains any non-US ASCII characters. */ static public boolean isAscii(String s) { for (int i = 0; i < s.length(); i++) {