Erkennen die URI-Codierung automatisch im Tomcat

Den komplizierten Weg, um zu erreichen mein Ziel war es, in der Tat schreiben, meinen eigenen javax.servlet.Filter und Einbettung in die Filterkette. Diese Lösung entspricht den Apache Tomcat Vorschlag in Tomcat Wiki - Character-Encoding-Probleme.

Update (2010-07-31): Die erste version dieses filters interpretiert den query-string selbst, das war eine schlechte Idee. Es hat nicht Griff POST Anfragen korrekt und hatte Probleme beim kombinieren mit anderen servlet-Filter wie für URL-rewriting. Diese version stattdessen wickelt der ursprünglich vorgesehenen Parameter und neu kodiert Sie. Um es richtig funktioniert, ist die URIEncoding (zum Beispiel Tomcat) müssen so konfiguriert werden, dass ISO-8859-1.

package de.roland_illig.webapps.webapp1;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CodingErrorAction;
import java.nio.charset.IllegalCharsetNameException;
import java.nio.charset.UnsupportedCharsetException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Enumeration;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.regex.Pattern;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;

/**
 * Automatically determines the encoding of the request parameters. It assumes
 * that the parameters of the original request are encoded by a 1:1 mapping from
 * bytes to characters.
 * <p>
 * If the request parameters cannot be decoded by any of the given encodings,
 * the filter chain is not processed further, but a status code of 400 with a
 * helpful error message is returned instead.
 * <p>
 * The filter can be configured using the following parameters:
 * <ul>
 * <li>{@code encodings}: The comma-separated list of encodings (see
 * {@link Charset#forName(String)}) that are tried in order. The first one that
 * can decode the complete query string is taken.
 * <p>
 * Default value: {@code UTF-8}
 * <p>
 * Example: {@code UTF-8,EUC-KR,ISO-8859-15}.
 * <li>{@code inputEncodingParameterName}: When this parameter is defined and a
 * query parameter of that name is provided by the client, and that parameter's
 * value contains only non-escaped characters and the server knows an encoding
 * of that name, then it is used exclusively, overriding the {@code encodings}
 * parameter for this request.
 * <p>
 * Default value: {@code null}
 * <p>
 * Example: {@code ie} (as used by Google).
 * </ul>
 */
public class EncodingFilter implements Filter {

  private static final Pattern PAT_COMMA = Pattern.compile(",\\s*");

  private String inputEncodingParameterName = null;
  private final List<Charset> encodings = new ArrayList<Charset>();

  @Override
  @SuppressWarnings("unchecked")
  public void init(FilterConfig config) throws ServletException {
    String encodingsStr = "UTF-8";

    Enumeration<String> en = config.getInitParameterNames();
    while (en.hasMoreElements()) {
      final String name = en.nextElement();
      final String value = config.getInitParameter(name);
      if (name.equals("encodings")) {
        encodingsStr = value;
      } else if (name.equals("inputEncodingParameterName")) {
        inputEncodingParameterName = value;
      } else {
        throw new IllegalArgumentException("Unknown parameter: " + name);
      }
    }

    for (String encoding : PAT_COMMA.split(encodingsStr)) {
      Charset charset = Charset.forName(encoding);
      encodings.add(charset);
    }
  }

  @SuppressWarnings("unchecked")
  @Override
  public void doFilter(ServletRequest sreq, ServletResponse sres, FilterChain fc) throws IOException, ServletException {
    final HttpServletRequest req = (HttpServletRequest) sreq;
    final HttpServletResponse res = (HttpServletResponse) sres;

    final Map<String, String[]> params;
    try {
      params = Util.decodeParameters(req.getParameterMap(), encodings, inputEncodingParameterName);
    } catch (IOException e) {
      res.sendError(400, e.getMessage());
      return;
    }

    HttpServletRequest wrapper = new ParametersWrapper(req, params);
    fc.doFilter(wrapper, res);
  }

  @Override
  public void destroy() {
    //nothing to do
  }

  static abstract class Util {

    static CharsetDecoder strictDecoder(Charset cs) {
      CharsetDecoder dec = cs.newDecoder();
      dec.onMalformedInput(CodingErrorAction.REPORT);
      dec.onUnmappableCharacter(CodingErrorAction.REPORT);
      return dec;
    }

    static int[] toCodePoints(String str) {
      final int len = str.length();
      int[] codePoints = new int[len];
      int i = 0, j = 0;
      while (i < len) {
        int cp = Character.codePointAt(str, i);
        codePoints[j++] = cp;
        i += Character.charCount(cp);
      }
      return j == len ? codePoints : Arrays.copyOf(codePoints, len);
    }

    public static String recode(String encoded, CharsetDecoder decoder) throws IOException {
      byte[] bytes = new byte[encoded.length()];
      int bytescount = 0;

      for (int i = 0; i < encoded.length(); i++) {
        char c = encoded.charAt(i);
        if (!(c <= '\u00FF'))
          throw new IOException("Invalid character: #" + (int) c);
        bytes[bytescount++] = (byte) c;
      }

      CharBuffer cbuf = decoder.decode(ByteBuffer.wrap(bytes, 0, bytescount));
      String result = cbuf.toString();
      return result;
    }

    static String ensureDefinedUnicode(String s) throws IOException {
      for (int cp : toCodePoints(s)) {
        if (!Character.isDefined(cp))
          throw new IOException("Undefined unicode code point: " + cp);
      }
      return s;
    }

    static Map<String, String[]> decodeParameters(Map<String, String[]> originalParams, List<Charset> charsets, String ieName) throws IOException {
      Map<String, String[]> params = new LinkedHashMap<String, String[]>();

      Charset ie = null;
      {
        String[] values = originalParams.get(ieName);
        if (values != null) {
          for (String value : values) {
            if (!value.isEmpty() && value.indexOf('%') == -1) {
              try {
                if (ie != null)
                  throw new IOException("Duplicate value for input encoding parameter: " + ie + " and " + value + ".");
                ie = Charset.forName(value);
              } catch (IllegalCharsetNameException e) {
                throw new IOException("Illegal input encoding name: " + value);
              } catch (UnsupportedCharsetException e) {
                throw new IOException("Unsupported input encoding: " + value);
              }
            }
          }
        }
      }

      Charset[] css = (ie != null) ? new Charset[] { ie } : charsets.toArray(new Charset[charsets.size()]);
      for (Charset charset : css) {
        try {
          params.clear();
          CharsetDecoder decoder = strictDecoder(charset);
          for (Map.Entry<String, String[]> entry : originalParams.entrySet()) {
            final String encodedName = entry.getKey();
            final String name = ensureDefinedUnicode(Util.recode(encodedName, decoder));
            for (final String encodedValue : entry.getValue()) {
              final String value = ensureDefinedUnicode(Util.recode(encodedValue, decoder));
              String[] oldValues = params.get(name);
              String[] newValues = (oldValues == null) ? new String[1] : Arrays.copyOf(oldValues, oldValues.length + 1);
              newValues[newValues.length - 1] = value;
              params.put(name, newValues);
            }
          }
          return params;
        } catch (IOException e) {
          continue;
        }
      }

      List<String> kvs = new ArrayList<String>();
      for (Map.Entry<String, String[]> entry : originalParams.entrySet()) {
        final String key = entry.getKey();
        for (final String value : entry.getValue()) {
          kvs.add(key + "=" + value);
        }
      }
      throw new IOException("Could not decode the parameters: " + kvs.toString());
    }
  }

  @SuppressWarnings("unchecked")
  static class ParametersWrapper extends HttpServletRequestWrapper {

    private final Map<String, String[]> params;

    public ParametersWrapper(HttpServletRequest request, Map<String, String[]> params) {
      super(request);
      this.params = params;
    }

    @Override
    public String getParameter(String name) {
      String[] values = params.get(name);
      return (values != null && values.length != 0) ? values[0] : null;
    }

    @Override
    public Map getParameterMap() {
      return Collections.unmodifiableMap(params);
    }

    @Override
    public Enumeration getParameterNames() {
      return Collections.enumeration(params.keySet());
    }

    @Override
    public String[] getParameterValues(String name) {
      return params.get(name);
    }
  }
}

Während die code-Größe ist relativ klein, es gibt einige Implementierungsdetails, die man bekommen kann, falsch ist, so hätte ich erwartet, dass Tomcat liefert bereits einen ähnlichen filter.

Um diesen filter zu aktivieren, habe ich die folgende für meine web.xml:

<filter>
  <filter-name>EncodingFilter</filter-name>
  <filter-class>de.roland_illig.webapps.webapp1.EncodingFilter</filter-class>
  <init-param>
    <param-name>encodings</param-name>
    <param-value>US-ASCII, UTF-8, EUC-KR, ISO-8859-15, ISO-8859-1</param-value>
  </init-param>
  <init-param>
    <param-name>inputEncodingParameterName</param-name>
    <param-value>ie</param-value>
  </init-param>
</filter>

<filter-mapping>
  <filter-name>EncodingFilter</filter-name>
  <url-pattern>/*</url-pattern>
</filter-mapping>