Character Encoding Issues
Questions
Answers
WhyWhat is the default character encoding of the request or response body? If a character encoding is not specified, the Servlet specification requires that an encoding of ISO-8859-1 is used. The character encoding for the body of an HTTP message (request or response) is specified in the Content-Type header field. An example of such a header is Content-Type: text/html; charset=ISO-8859-1 which explicitly states that the default (ISO-8859-1) is being used. References: HTTP 1.1 Specification, Section 3.7.1 The above general rules apply to Servlets. The behaviour of JSP pages is further specified by the JSP specification. The request character encoding handling is the same, but response character encoding behaves a bit differently. See chapter "JSP.4.2 Response Character Encoding". For JSP pages in standard syntax the default response charset is the usual ISO-8859-1, but for the ones in XML syntax it is UTF-8.
Why does everything have to be this way? Everything covered in this page comes down to practical interpretation of a number of specifications. When working with Java servlets, the Java Servlet Specification is the primary reference, but the servlet spec itself relies on older specifications such as HTTP for its foundation. Here are a couple of references before we cover exactly where these items are located in them. Default encoding for request and response bodies See 'Default Encoding for POST' below. Default encoding for GET The character set for HTTP query strings (that's the technical term for 'GET parameters') can be found in sections 2 and 2.1 the "URI Syntax" specification. The character set is defined to be US-ASCII. Any character that does not map to US-ASCII must be encoded in some way. Section 2.1 of the URI Syntax specification says that characters outside of US-ASCII must be encoded using % escape sequences: each character is encoded as a literal % followed by the two hexadecimal codes which indicate its character code. Thus, a (US-ASCII character code 97 = 0x61) is equivalent to %61. There is no default encoding for URIs specified anywhere, which is why there is a lot of confusion when it comes to decoding these values. Some notes about the character encoding of URIs:
Default Encoding for POST ISO-8859-1 is defined as the default character set for HTTP request and response bodies in the servlet specification (request encoding: section 4.9 for spec version 2.4, section 3.9 for spec version 2.5; response encoding: section 5.4 for both spec versions 2.4 and 2.5). This default is historical: it comes from sections 3.4.1 and 3.7.1 of the HTTP/1.1 specification. Some notes about the character encoding of a POST request:
HTTP Headers Section 3.1 of the ARPA Internet Text Messages spec states that headers are always in US-ASCII encoding. Anything outside of that needs to be encoded. See the section above regarding query strings in URIs.
HowHow do I change how GET parameters are interpreted? Tomcat will use ISO-8859-1 as the default character encoding of the entire URL, including the query string ("GET parameters"). There are two ways to specify how GET parameters are interpreted:
References: Tomcat 6 HTTP Connector, Tomcat 6 AJP Connector
How do I change how POST parameters are interpreted? POST requests should specify the encoding of the parameters and values they send. Since many clients fail to set an explicit encoding, the default is used (ISO-8859-1). In many cases this is not the preferred interpretation so one can employ a javax.servlet.Filter to set request encodings. Writing such a filter is trivial. Furthermore Tomcat already comes with such an example filter. Please take a look at:
webapps/servlets-examples/WEB-INF/classes/filters/SetCharacterEncodingFilter.java webapps/jsp-examples/WEB-INF/classes/filters/SetCharacterEncodingFilter.java
webapps/examples/WEB-INF/classes/filters/SetCharacterEncodingFilter.java
Since 7.0.20 the filter became first-class citizen and was moved from the examples into core Tomcat and is available to any web application without the need to compile and bundle it separately. See documentation for the list of filters provided by Tomcat. The class name is: org.apache.catalina.filters.SetCharacterEncodingFilter It was also ported to older Tomcat versions and is available there starting with versions 5.5.36 and 6.0.36. (not yet released at the time of this writing) Note: The request encoding setting is effective only if it is done earlier than parameters are parsed. Once parsing happens, there is no way back. Parameters parsing is triggered by the first method that asks for parameter name or value. Make sure that the filter is positioned before any other filters that ask for request parameters. The positioning depends on the order of filter-mapping declarations in the WEB-INF/web.xml file, though since Servlet 3.0 specification there are additional options to control the order. To check the actual order you can throw an Exception from your page and check its stack trace for filter names.
What can you recommend to just make everything work? (How to use UTF-8 everywhere). Using UTF-8 as your character encoding for everything is a safe bet. This should work for pretty much every situation. In order to completely switch to using UTF-8, you need to make the following changes:
How can I test if my configuration will work correctly? The following sample JSP should work on a clean Tomcat install for any input. If you set the URIEncoding="UTF-8" on the connector, it will also work with method="GET". <%@ page contentType="text/html; charset=UTF-8" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Character encoding test page</title>
</head>
<body>
<p>Data posted to this form was:
<%
request.setCharacterEncoding("UTF-8");
out.print(request.getParameter("mydata"));
%>
</p>
<form method="POST" action="index.jsp">
<input type="text" name="mydata">
<input type="submit" value="Submit" />
<input type="reset" value="Reset" />
</form>
</body>
</html>
About the request.setCharacterEncoding() and response.setCharacterEncoding() request.setCharacterEncoding() must be invoked before the request parameters be asked. resp.setCharacterEncoding("iso-8859-1"); // will not write into http head. resp.setContentType("text/html; charset=utf-8"); // will write into http head. And no matter which method in the first, the second will always overrides the first one. |
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