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Java example source code file (ServletUtils.java)

This example Java source code file (ServletUtils.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

arraylist, ascii, byteaccumulator, charset, http, httpservletrequest, list, non-ascii, numberformatexception, request, response, servlet, servletutils, slash_joiner, slash_splitter, string, stringbuilder, utf_8, util

The ServletUtils.java Java example source code

/**
 * Copyright (C) 2012 Google Inc.
 *
 * 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.inject.servlet;

import static com.google.common.base.Charsets.UTF_8;
import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.base.Joiner;
import com.google.common.base.Splitter;
import com.google.common.net.UrlEscapers;

import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import javax.servlet.http.HttpServletRequest;

/**
 * Some servlet utility methods.
 *
 * @author ntang@google.com (Michael Tang)
 */
final class ServletUtils {
  private static final Splitter SLASH_SPLITTER = Splitter.on('/');
  private static final Joiner SLASH_JOINER = Joiner.on('/');

  private ServletUtils() {
    // private to prevent instantiation.
  }

  /**
   * Gets the context path relative path of the URI. Returns the path of the
   * resource relative to the context path for a request's URI, or null if no
   * path can be extracted.
   *
   * <p>Also performs url decoding and normalization of the path.
   */
  // @Nullable
  static String getContextRelativePath(
      // @Nullable
      final HttpServletRequest request) {
    if (request != null) {
      String contextPath = request.getContextPath();
      String requestURI = request.getRequestURI();
      if (contextPath.length() < requestURI.length()) {
        String suffix = requestURI.substring(contextPath.length());
        return normalizePath(suffix);
      } else if (requestURI.trim().length() > 0 &&
          contextPath.length() == requestURI.length()) {
        return "/";
      }
    }
    return null;
  }

  /**
   * Normalizes a path by unescaping all safe, percent encoded characters.
   */
  static String normalizePath(String path) {
    StringBuilder sb = new StringBuilder(path.length());
    int queryStart = path.indexOf('?');
    String query = null;
    if (queryStart != -1) {
      query = path.substring(queryStart);
      path = path.substring(0, queryStart);
    }
    // Normalize the path.  we need to decode path segments, normalize and rejoin in order to
    // 1. decode and normalize safe percent escaped characters.  e.g. %70 -> 'p'
    // 2. decode and interpret dangerous character sequences. e.g. /%2E/ -> '/./' -> '/'
    // 3. preserve dangerous encoded characters. e.g. '/%2F/' -> '///' -> '/%2F'
    List<String> segments = new ArrayList();
    for (String segment : SLASH_SPLITTER.split(path)) {
      // This decodes all non-special characters from the path segment.  so if someone passes
      // /%2E/foo we will normalize it to /./foo and then /foo
      String normalized =
          UrlEscapers.urlPathSegmentEscaper().escape(lenientDecode(segment, UTF_8, false));
      if (".".equals(normalized)) {
        // skip
      } else if ("..".equals(normalized)) {
        if (segments.size() > 1) {
          segments.remove(segments.size() - 1);
        }
      } else {
        segments.add(normalized);
      }
    }
    SLASH_JOINER.appendTo(sb, segments);
    if (query != null) {
      sb.append(query);
    }
    return sb.toString();
  }


  /**
   * Percent-decodes a US-ASCII string into a Unicode string. The specified
   * encoding is used to determine what characters are represented by any
   * consecutive sequences of the form "%<i>XX". This is the lenient
   * kind of decoding that will simply ignore and copy as-is any "%XX"
   * sequence that is invalid (for example, "%HH").
   *
   * @param string a percent-encoded US-ASCII string
   * @param encoding a character encoding
   * @param decodePlus boolean to indicate whether to decode '+' as ' '
   * @return a Unicode string
   */
  private static String lenientDecode(String string, Charset encoding, boolean decodePlus) {

    checkNotNull(string);
    checkNotNull(encoding);

    if (decodePlus) {
      string = string.replace('+', ' ');
    }

    int firstPercentPos = string.indexOf('%');

    if (firstPercentPos < 0) {
      return string;
    }

    ByteAccumulator accumulator =
        new ByteAccumulator(string.length(), encoding);
    StringBuilder builder = new StringBuilder(string.length());

    if (firstPercentPos > 0) {
      builder.append(string, 0, firstPercentPos);
    }

    for (int srcPos = firstPercentPos; srcPos < string.length(); srcPos++) {

      char c = string.charAt(srcPos);

      if (c < 0x80) {  // ASCII
        boolean processed = false;

        if (c == '%' && string.length() >= srcPos + 3) {
          String hex = string.substring(srcPos + 1, srcPos + 3);

          try {
            int encoded = Integer.parseInt(hex, 16);

            if (encoded >= 0) {
              accumulator.append((byte) encoded);
              srcPos += 2;
              processed = true;
            }
          } catch (NumberFormatException ignore) {
            // Expected case (badly formatted % group)
          }
        }

        if (!processed) {
          if (accumulator.isEmpty()) {
            // We're not accumulating elements of a multibyte encoded
            // char, so just toss it right into the result string.

            builder.append(c);
          } else {
            accumulator.append((byte) c);
          }
        }
      } else {  // Non-ASCII
        // A non-ASCII char marks the end of a multi-char encoding sequence,
        // if one is in progress.

        accumulator.dumpTo(builder);
        builder.append(c);
      }
    }

    accumulator.dumpTo(builder);

    return builder.toString();
  }

  /**
   * Accumulates byte sequences while decoding strings, and
   * encodes them into a StringBuilder.
   */
  private static class ByteAccumulator {
    private byte[] bytes;
    private int length;
    private final Charset encoding;

    ByteAccumulator(int capacity, Charset encoding) {
      this.bytes = new byte[Math.min(16, capacity)];
      this.encoding = encoding;
    }

    void append(byte b) {
      ensureCapacity(length + 1);
      bytes[length++] = b;
    }

    void dumpTo(StringBuilder dest) {
      if (length != 0) {
        dest.append(new String(bytes, 0, length, encoding));
        length = 0;
      }
    }

    boolean isEmpty() {
      return length == 0;
    }

    private void ensureCapacity(int minCapacity) {
      if (bytes.length >= minCapacity) {
        return;
      }
      int newCapacity = bytes.length + bytes.length >> 1;  // *1.5
      if (newCapacity < minCapacity) {
        // we are close to overflowing, grow by smaller steps
        newCapacity = minCapacity;
      }
      // in other cases, we will naturally throw an OOM from here
      bytes = Arrays.copyOf(bytes, newCapacity);
    }
  }

}

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