我有一个正在运行的 Apache Tomcat 6.x 实例，我希望它能够比默认行为更智能地解释传入 URL 的字符集。我特别想实现如下映射：
So%DFe => Soße
So%C3%9Fe => Soße
So%DF%C3%9F => (error)
我想要的行为可以描述为“尝试将字节流解码为 UTF-8，如果它不起作用则假设 ISO-8859-1”。
在这种情况下，仅使用 URIEncoding 配置不起作用。那么如何配置 Tomcat 以按照我想要的方式对请求进行编码呢？
我可能需要编写一个过滤器来接收请求（尤其是查询字符串）并将其重新编码为参数。那是自然的方式吗？
【问题讨论】：
标签： java tomcat character-encoding servlet-filters url-encoding
实现我的目标的复杂方法确实是编写我自己的javax.servlet.Filter 并将其嵌入到过滤器链中。此解决方案符合Tomcat Wiki - Character Encoding Issues 中提供的 Apache Tomcat 建议。
更新 (2010-07-31)： 此过滤器的第一个版本解释了查询字符串本身，这是一个坏主意。它不能正确处理POST 请求，并且在与其他 servlet 过滤器（如 URL 重写）结合使用时会出现问题。这个版本改为包装最初提供的参数并重新编码。要使其正常工作，URIEncoding（例如在 Tomcat 中）必须配置为 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);
}
}
}
虽然代码相当小，但有一些实现细节可能会出错，所以我原以为 Tomcat 已经提供了类似的过滤器。
要激活此过滤器，我已将以下内容添加到我的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>
【讨论】：
我们已经在 SGES2.1.1 上做了类似 Roland 的解决方案（我认为它使用 catalina 和一些旧的 Tomcat 一样），但它有一些问题：
今天，在阅读了许多博客和建议后，我删除了整个类，只做了一件简单的事情：从包装器构造函数中的 Content-Type 标头解析字符集并将其设置为包装实例。
成功了，我们所有的 988 测试都成功了。
private static final Pattern CHARSET_PATTERN
= Pattern.compile("(?i)\\bcharset=\\s*\"?([^\\s;\"]*)");
private static final String CHARSET_DEFAULT = "ISO-8859-2";
public CisHttpRequestWrapper(final HttpServletRequest request) {
super(request);
if (request.getCharacterEncoding() != null) {
return;
}
final String charset = parseCharset(request);
try {
setCharacterEncoding(charset);
} catch (final UnsupportedEncodingException e) {
throw new IllegalStateException("Unknown charset: " + charset, e);
}
}
private String parseCharset(final HttpServletRequest request) {
final String contentType = request.getHeader("Content-Type");
if (contentType == null || contentType.isEmpty()) {
return CHARSET_DEFAULT;
}
final Matcher m = CHARSET_PATTERN.matcher(contentType);
if (!m.find()) {
return CHARSET_DEFAULT;
}
final String charsetName = m.group(1).trim().toUpperCase();
return charsetName;
}
【讨论】：