1 /* 2 * Copyright (C) 2008 Google Inc. 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 package com.android.mail.lib.base; 17 18 /** 19 * An object that converts literal text into a format safe for inclusion in a particular context 20 * (such as an XML document). Typically (but not always), the inverse process of "unescaping" the 21 * text is performed automatically by the relevant parser. 22 * 23 * <p>For example, an XML escaper would convert the literal string {@code "Foo<Bar>"} into {@code 24 * "Foo<Bar>"} to prevent {@code "<Bar>"} from being confused with an XML tag. When the 25 * resulting XML document is parsed, the parser API will return this text as the original literal 26 * string {@code "Foo<Bar>"}. 27 * 28 * <p>An {@code Escaper} instance is required to be stateless, and safe when used concurrently by 29 * multiple threads. 30 * 31 * <p>The two primary implementations of this interface are {@link CharEscaper} and {@link 32 * UnicodeEscaper}. They are heavily optimized for performance and greatly simplify the task of 33 * implementing new escapers. It is strongly recommended that when implementing a new escaper you 34 * extend one of these classes. If you find that you are unable to achieve the desired behavior 35 * using either of these classes, please contact the Java libraries team for advice. 36 * 37 * <p>Several popular escapers are defined as constants in the class {@link CharEscapers}. To create 38 * your own escapers, use {@link CharEscaperBuilder}, or extend {@link CharEscaper} or {@code 39 * UnicodeEscaper}. 40 * 41 * @author dbeaumont (at) google.com (David Beaumont) 42 */ 43 public abstract class Escaper { 44 /** 45 * Returns the escaped form of a given literal string. 46 * 47 * <p>Note that this method may treat input characters differently depending on the specific 48 * escaper implementation. 49 * 50 * <ul> 51 * <li>{@link UnicodeEscaper} handles <a href="http://en.wikipedia.org/wiki/UTF-16">UTF-16</a> 52 * correctly, including surrogate character pairs. If the input is badly formed the escaper 53 * should throw {@link IllegalArgumentException}. 54 * <li>{@link CharEscaper} handles Java characters independently and does not verify the input 55 * for well formed characters. A CharEscaper should not be used in situations where input is 56 * not guaranteed to be restricted to the Basic Multilingual Plane (BMP). 57 * </ul> 58 * 59 * @param string the literal string to be escaped 60 * @return the escaped form of {@code string} 61 * @throws NullPointerException if {@code string} is null 62 * @throws IllegalArgumentException if {@code string} contains badly formed UTF-16 or cannot be 63 * escaped for any other reason 64 */ 65 public abstract String escape(String string); 66 67 /** 68 * Returns an {@code Appendable} instance which automatically escapes all text appended to it 69 * before passing the resulting text to an underlying {@code Appendable}. 70 * 71 * <p>Note that the Appendable returned by this method may treat input characters differently 72 * depending on the specific escaper implementation. 73 * 74 * <ul> 75 * <li>{@link UnicodeEscaper} handles <a href="http://en.wikipedia.org/wiki/UTF-16">UTF-16</a> 76 * correctly, including surrogate character pairs. If the input is badly formed the escaper 77 * should throw {@link IllegalArgumentException}. 78 * <li>{@link CharEscaper} handles Java characters independently and does not verify the input 79 * for well formed characters. A CharEscaper should not be used in situations where input is 80 * not guaranteed to be restricted to the Basic Multilingual Plane (BMP). 81 * </ul> 82 * 83 * <p>In all implementations the escaped Appendable should throw {@code NullPointerException} if 84 * given a {@code null} {@link CharSequence}. 85 * 86 * @param out the underlying {@code Appendable} to append escaped output to 87 * @return an {@code Appendable} which passes text to {@code out} after escaping it 88 */ 89 public abstract Appendable escape(Appendable out); 90 91 private final Function<String, String> asFunction = 92 new Function<String, String>() { 93 public String apply(String from) { 94 return escape(from); 95 } 96 }; 97 98 /** 99 * Returns a {@link Function} that invokes {@link #escape(String)} on this escaper. 100 */ 101 public Function<String, String> asFunction() { 102 return asFunction; 103 } 104 }
