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  /*
   * Copyright (C) 2006 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
   *
   * 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.google.common.escape;
 
 import static com.google.common.base.Preconditions.checkNotNull;
 
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>".

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

Several popular escapers are defined as constants in classes like com.google.common.html.HtmlEscapers, com.google.common.xml.XmlEscapers, and SourceCodeEscapers. To create your own escapers extend this class and implement the escape(char) method.

Author(s):
Sven Mawson
Since:
15.0
 
 public abstract class CharEscaper extends Escaper {
  
Constructor for use by subclasses.
 
   protected CharEscaper() {}

  
Returns the escaped form of a given literal string.

Parameters:
string the literal string to be escaped
Returns:
the escaped form of string
Throws:
java.lang.NullPointerException if string is null
 
   @Override public String escape(String string) {
     checkNotNull(string);  // GWT specific check (do not optimize)
     // Inlineable fast-path loop which hands off to escapeSlow() only if needed
     int length = string.length();
     for (int index = 0; index < lengthindex++) {
       if (escape(string.charAt(index)) != null) {
         return escapeSlow(stringindex);
       }
     }
     return string;
   }

  
Returns the escaped form of a given literal string, starting at the given index. This method is called by the escape(java.lang.String) method when it discovers that escaping is required. It is protected to allow subclasses to override the fastpath escaping function to inline their escaping test. See CharEscaperBuilder for an example usage.

Parameters:
s the literal string to be escaped
index the index to start escaping from
Returns:
the escaped form of string
Throws:
java.lang.NullPointerException if string is null
 
   protected final String escapeSlow(String sint index) {
     int slen = s.length();
 
     // Get a destination buffer and setup some loop variables.
     char[] dest = Platform.charBufferFromThreadLocal();
     int destSize = dest.length;
     int destIndex = 0;
     int lastEscape = 0;
 
     // Loop through the rest of the string, replacing when needed into the
     // destination buffer, which gets grown as needed as well.
     for (; index < slenindex++) {
 
       // Get a replacement for the current character.
       char[] r = escape(s.charAt(index));
 
       // If no replacement is needed, just continue.
       if (r == nullcontinue;
 
      int rlen = r.length;
      int charsSkipped = index - lastEscape;
      // This is the size needed to add the replacement, not the full size
      // needed by the string. We only regrow when we absolutely must.
      int sizeNeeded = destIndex + charsSkipped + rlen;
      if (destSize < sizeNeeded) {
        destSize = sizeNeeded + (slen - index) + ;
        dest = growBuffer(destdestIndexdestSize);
      }
      // If we have skipped any characters, we need to copy them now.
      if (charsSkipped > 0) {
        s.getChars(lastEscapeindexdestdestIndex);
        destIndex += charsSkipped;
      }
      // Copy the replacement string into the dest buffer as needed.
      if (rlen > 0) {
        System.arraycopy(r, 0, destdestIndexrlen);
        destIndex += rlen;
      }
      lastEscape = index + 1;
    }
    // Copy leftover characters if there are any.
    int charsLeft = slen - lastEscape;
    if (charsLeft > 0) {
      int sizeNeeded = destIndex + charsLeft;
      if (destSize < sizeNeeded) {
        // Regrow and copy, expensive! No padding as this is the final copy.
        dest = growBuffer(destdestIndexsizeNeeded);
      }
      s.getChars(lastEscapeslendestdestIndex);
      destIndex = sizeNeeded;
    }
    return new String(dest, 0, destIndex);
  }

  
Returns the escaped form of the given character, or null if this character does not need to be escaped. If an empty array is returned, this effectively strips the input character from the resulting text.

If the character does not need to be escaped, this method should return null, rather than a one-character array containing the character itself. This enables the escaping algorithm to perform more efficiently.

An escaper is expected to be able to deal with any char value, so this method should not throw any exceptions.

Parameters:
c the character to escape if necessary
Returns:
the replacement characters, or null if no escaping was needed
  protected abstract char[] escape(char c);

  
Helper method to grow the character buffer as needed, this only happens once in a while so it's ok if it's in a method call. If the index passed in is 0 then no copying will be done.
  private static char[] growBuffer(char[] destint indexint size) {
    char[] copy = new char[size];
    if (index > 0) {
      System.arraycopy(dest, 0, copy, 0, index);
    }
    return copy;
  }

  
The amount of padding to use when growing the escape buffer.
  private static final int DEST_PAD = 32;
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