chararray.java

OS(OpenSymphony)的SiteMesh是一个用来在JSP中实现页面布局和装饰（layout and decoration）的框架组件

package com.opensymphony.module.sitemesh.html.util;

import java.io.PrintWriter;

/**
 * A leaner, meaner version of StringBuffer.
 * <p/>
 * It provides basic functionality to handle dynamically-growing
 * char arrays as quickly as possible. This class is not threadsafe.
 * 
 * @author Chris Miller
 */
public class CharArray
{
   int size = 0;
   char[] buffer;

   // These properties allow us to specify a substring within the character array
   // that we can perform comparisons against. This is here purely for performance -
   // the comparisons are at the heart of the FastPageParser loop and any speed increase
   // we can get at this level has a huge impact on performance.
   int subStrStart = 0;
   int subStrLen = 0;

   /**
    * Constructs a CharArray that is initialized to the specified size.
    *
    * Do not pass in a negative value because there is no bounds checking!
    */
   public CharArray(int size)
   {
      buffer = new char[size];
   }

   /**
    * Returns a String represenation of the character array.
    */
   public String toString()
   {
      return new String(buffer, 0, size);
   }

   /**
    * Returns the character that is at the specified position in the array.
    *
    * There is no bounds checking on this method so be sure to pass in a
    * sensible value.
    */
   public char charAt(int pos)
   {
      return buffer[pos];
   }

   /**
    * Changes the size of the character array to the value specified.
    *
    * If the new size is less than the current size, the data in the
    * internal array will be truncated. If the new size is &lt;= 0,
    * the array will be reset to empty (but, unlike StringBuffer, the
    * internal array will NOT be shrunk). If the new size is &gt the
    * current size, the array will be padded out with null characters
    * (<tt>'&#92;u0000'</tt>).
    *
    * @param newSize the new size of the character array
    */
   public void setLength(int newSize)
   {
      if (newSize < 0)
      {
         newSize = 0;
      }

      if (newSize <= size)
      {
         size = newSize;
      }
      else
      {
         if (newSize >= buffer.length)
            grow(newSize);
         // Pad the array
         for (; size < newSize; size++)
                buffer[size] = '\0';
      }
   }

   /**
    * Returns the current length of the character array.
    */
   public int length()
   {
      return size;
   }

   /**
    * Appends an existing CharArray on to this one.
    *
    * Passing in a <tt>null</tt> CharArray will result in a <tt>NullPointerException</tt>.
    */
   public CharArray append(CharArray chars)
   {
      return append(chars.buffer, 0, chars.size);
   }

   /**
    * Appends the supplied characters to the end of the array.
    */
   public CharArray append(char[] chars)
   {
      return append(chars, 0, chars.length);
   }

   public CharArray append(char[] chars, int position, int length)
   {
       int requiredSize = length + size;
       if (requiredSize >= buffer.length)
          grow(requiredSize);
       System.arraycopy(chars, position, buffer, size, length);
       size = requiredSize;
       return this;
   }

   /**
    * Appends a single character to the end of the character array.
    */
   public CharArray append(char c)
   {
      if (buffer.length == size)
         grow(0);
      buffer[size++] = c;
      return this;
   }

   /**
    * Appends the supplied string to the end of this character array.
    *
    * Passing in a <tt>null</tt> string will result in a <tt>NullPointerException</tt>.
    */
   public CharArray append(String str)
   {
      int requiredSize = str.length() + size;
      if (requiredSize >= buffer.length)
         grow(requiredSize);

      for (int i = 0; i < str.length(); i++)
         buffer[size + i] = str.charAt(i);

      size = requiredSize;
      return this;
   }

   /**
    * Returns a substring from within this character array.
    *
    * Note that NO range checking is performed!
    */
   public String substring(int begin, int end)
   {
      return new String(buffer, begin, end - begin);
   }

   /**
    * Allows an arbitrary substring of this character array to be specified.
    * This method should be called prior to calling {@link #compareLowerSubstr(String)}
    * to set the range of the substring comparison.
    *
    * @param begin the starting offset into the character array.
    * @param end the ending offset into the character array.
    */
   public void setSubstr(int begin, int end)
   {
      subStrStart = begin;
      subStrLen = end - begin;
   }

   /**
    * Returns the substring that was specified by the {@link #setSubstr(int, int)} call.
    */
   public String getLowerSubstr()
   {
      for (int i = subStrStart; i < subStrStart + subStrLen; i++)
         buffer[i] |= 32;
      return new String(buffer, subStrStart, subStrLen);
   }

   /**
    * This compares a substring of this character array (as specified
    * by the {@link #setSubstr(int, int)} method call) with the supplied
    * string. The supplied string <em>must</em> be lowercase, otherwise
    * the comparison will fail.
    */
   public boolean compareLowerSubstr(String lowerStr)
   {
      // Range check
      if (lowerStr.length() != subStrLen || subStrLen <= 0)
         return false;

      for (int i = 0; i < lowerStr.length(); i++) {
         // | 32 converts from ASCII uppercase to ASCII lowercase
         if ((buffer[subStrStart + i] | 32) != lowerStr.charAt(i))
            return false;
      }
      return true;
   }

   /**
    * Returns the hashcode for a <em>lowercase</em> version of the array's substring
    * (as set by the {@link #setSubstr(int, int)} method).
    *
    * This uses the same calculation as the <tt>String.hashCode()</tt> method
    * so that it remains compatible with the hashcodes of normal strings.
    */
   public int substrHashCode()
   {
      int hash = 0;
      int offset = subStrStart;
      for (int i = 0; i < subStrLen; i++) {
         hash = 31 * hash + (buffer[offset++] | 32);
      }
      return hash;
   }

   /**
    * Compares the supplied uppercase string with the contents of
    * the character array, starting at the offset specified.
    *
    * This is a specialized method to help speed up the FastPageParser
    * slightly.
    * <p/>
    * The supplied string is assumed to contain only uppercase ASCII
    * characters. The offset indicates the offset into the character
    * array that the comparison should start from.
    * <p/>
    * If (and only if) the supplied string and the relevant portion of the
    * character array are considered equal, this method will return <tt>true</tt>.
    */
   public boolean compareLower(String lowerStr, int offset)
   {
      // Range check
      if (offset < 0 || offset + lowerStr.length() > size)
         return false;

      for (int i = 0; i < lowerStr.length(); i++)
      {
         // | 32 converts from ASCII uppercase to ASCII lowercase
         if ((buffer[offset + i] | 32) != lowerStr.charAt(i))
            return false;
      }
      return true;
   }

   /**
    * Grows the internal array by either ~100% or minSize (whichever is larger),
    * up to a maximum size of Integer.MAX_VALUE.
    */
   private final void grow(int minSize)
   {
      int newCapacity = (buffer.length + 1) * 2;
      if (newCapacity < 0)
      {
         newCapacity = Integer.MAX_VALUE;
      }
      else if (minSize > newCapacity)
      {
         newCapacity = minSize;
      }
      char newBuffer[] = new char[newCapacity];
      System.arraycopy(buffer, 0, newBuffer, 0, size);
      buffer = newBuffer;
   }

    /**
     * Clear the contents.
     */
    public final void clear()
    {
        size = 0;
    }

    public void writeTo(PrintWriter writer)
    {
        writer.write(buffer, 0, size);
    }
}