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   * Copyright (C) 2008 The Guava Authors
   * Licensed 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
  * 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.
An object that converts literal text into a format safe for inclusion in a particular context (such as an XML document). Typically (but not always), the inverse process of "unescaping" the text is performed automatically by the relevant parser.

For example, an XML escaper would convert the literal string "Foo<Bar>" into "Foo&lt;Bar&gt;" to prevent "<Bar>" from being confused with an XML tag. When the resulting XML document is parsed, the parser API will return this text as the original literal string "Foo<Bar>".

An Escaper instance is required to be stateless, and safe when used concurrently by multiple threads.

Because, in general, escaping operates on the code points of a string and not on its individual char values, it is not safe to assume that escape(s) is equivalent to escape(s.substring(0, n)) + escape(s.substing(n)) for arbitrary n. This is because of the possibility of splitting a surrogate pair. The only case in which it is safe to escape strings and concatenate the results is if you can rule out this possibility, either by splitting an existing long string into short strings adaptively around java.lang.Character.isHighSurrogate(char) pairs, or by starting with short strings already known to be free of unpaired surrogates.

The two primary implementations of this interface are CharEscaper and UnicodeEscaper. They are heavily optimized for performance and greatly simplify the task of implementing new escapers. It is strongly recommended that when implementing a new escaper you extend one of these classes. If you find that you are unable to achieve the desired behavior using either of these classes, please contact the Java libraries team for advice.

Several popular escapers are defined as constants in classes like,, and SourceCodeEscapers. To create your own escapers, use CharEscaperBuilder, or extend CharEscaper or UnicodeEscaper.

David Beaumont
 public abstract class Escaper {
   // TODO(user): evaluate custom implementations, considering package private constructor.
Constructor for use by subclasses.
   protected Escaper() {}

Returns the escaped form of a given literal string.

Note that this method may treat input characters differently depending on the specific escaper implementation.

  • UnicodeEscaper handles UTF-16 correctly, including surrogate character pairs. If the input is badly formed the escaper should throw java.lang.IllegalArgumentException.
  • CharEscaper handles Java characters independently and does not verify the input for well formed characters. A CharEscaper should not be used in situations where input is not guaranteed to be restricted to the Basic Multilingual Plane (BMP).

string the literal string to be escaped
the escaped form of string
java.lang.NullPointerException if string is null
java.lang.IllegalArgumentException if string contains badly formed UTF-16 or cannot be escaped for any other reason
   public abstract String escape(String string);
   private final Function<StringStringasFunction =
       new Function<StringString>() {
         public String apply(String from) {
           return escape(from);

Returns a that invokes escape(java.lang.String) on this escaper.
  public final Function<StringStringasFunction() {
    return ;
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