Tomcat+MySql+Struts的中文问题 [过滤器]

开发Web应用程序时，无论是用什么样的框架技术来开发，一碰从数据库存取涉及到中文的数据，就要面对中文乱码或者是各种编码方式不匹配的异常，今天晚上终于搞定了Tomcat+MySql+Struts的中文问题，用到了很简单的方法，很快就能搞定。

    在做以下工作之前，所有的HTML/JSP的charset都设为charset=gb2312。

    第一个要解决的是表单提交乱码问题。在使用Struts提供的ActionForm过程中，无论表单采用的是Struts标签还是Html标签，都可以用ActionForm的Get/Set来获取和设置表单的元素值（它们的作用效果与request.getParameter()方法一样），但提取出来的数据不经过处理的话就是乱码，主要的原因是1.Tomcat的J2EE实现对表单提交即Post方法提交时，处理参数采用默认的ISO8859_1来处理2.Tomcat对Get方法提交的请求在query-string处理时采用了和Post方法不一样的处理方式。所以如果要正确地显示和获取中文数据采用的解决方案：（1）对于Post方法提交的表单通过编写一个过滤器（filer）的方法解决，过滤器在用户提交的数据被处理之前被调用，可以通过这个Java代码改变参数的编码方式（目标编码方式可以通过Web.xml文件里面的参数指定）。过滤器的代码如下：

import java.io.IOException;
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.UnavailableException;


/**
* <p>Example filter that sets the character encoding to be used in parsing the
* incoming request, either unconditionally or only if the client did not
* specify a character encoding.  Configuration of this filter is based on
* the following initialization parameters:</p>
* <ul>
* <li><strong>encoding</strong> - The character encoding to be configured
*     for this request, either conditionally or unconditionally based on
*     the <code>ignore</code> initialization parameter.  This parameter
*     is required, so there is no default.</li>
* <li><strong>ignore</strong> - If set to "true", any character encoding
*     specified by the client is ignored, and the value returned by the
*     <code>selectEncoding()</code> method is set.  If set to "false,
*     <code>selectEncoding()</code> is called <strong>only</strong> if the
*     client has not already specified an encoding.  By default, this
*     parameter is set to "true".</li>
* </ul>
*
* <p>Although this filter can be used unchanged, it is also easy to
* subclass it and make the <code>selectEncoding()</code> method more
* intelligent about what encoding to choose, based on characteristics of
* the incoming request (such as the values of the <code>Accept-Language</code>
* and <code>User-Agent</code> headers, or a value stashed in the current
* user’s session.</p>
*
* @author Craig McClanahan
* @version $Revision: 1.2 $ $Date: 2004/03/18 16:40:33 $
*/

public class SetCharacterEncodingFilter implements Filter {


    // ----------------------------------------------------- Instance Variables


    /**
     * The default character encoding to set for requests that pass through
     * this filter.
     */
    protected String encoding = null;


    /**
     * The filter configuration object we are associated with.  If this value
     * is null, this filter instance is not currently configured.
     */
    protected FilterConfig filterConfig = null;


    /**
     * Should a character encoding specified by the client be ignored?
     */
    protected boolean ignore = true;


    // --------------------------------------------------------- Public Methods


    /**
     * Take this filter out of service.
     */
    public void destroy() {

        this.encoding = null;
        this.filterConfig = null;

    }


    /**
     * Select and set (if specified) the character encoding to be used to
     * interpret request parameters for this request.
     *
     * @param request The servlet request we are processing
     * @param result The servlet response we are creating
     * @param chain The filter chain we are processing
     *
     * @exception IOException if an input/output error occurs
     * @exception ServletException if a servlet error occurs
     */
    public void doFilter(ServletRequest request, ServletResponse response,
                         FilterChain chain)
throws IOException, ServletException {

        // Conditionally select and set the character encoding to be used
        if (ignore || (request.getCharacterEncoding() == null)) {
            String encoding = selectEncoding(request);
            if (encoding != null)
                request.setCharacterEncoding(encoding);
        }

// Pass control on to the next filter
        chain.doFilter(request, response);

    }


    /**
     * Place this filter into service.
     *
     * @param filterConfig The filter configuration object
     */
    public void init(FilterConfig filterConfig) throws ServletException {

this.filterConfig = filterConfig;
        this.encoding = filterConfig.getInitParameter("encoding");
        String value = filterConfig.getInitParameter("ignore");
        if (value == null)
            this.ignore = true;
        else if (value.equalsIgnoreCase("true"))
            this.ignore = true;
        else if (value.equalsIgnoreCase("yes"))
            this.ignore = true;
        else
            this.ignore = false;

    }


    // ------------------------------------------------------ Protected Methods


    /**
     * Select an appropriate character encoding to be used, based on the
     * characteristics of the current request and/or filter initialization
     * parameters.  If no character encoding should be set, return
     * <code>null</code>.
     * <p>
     * The default implementation unconditionally returns the value configured
     * by the <strong>encoding</strong> initialization parameter for this
     * filter.
     *
     * @param request The servlet request we are processing
     */
    protected String selectEncoding(ServletRequest request) {

        return (this.encoding);

    }

}

编绎后把class文件放在classes目录下，并在Web应用的web.xml文件中添加如下代码：

<filter>
  <filter-name>Set Character Encoding</filter-name>
  <filter-class>com.neusoft.equipment.controller.SetCharacterEncodingFilter</filter-class>
  <init-param>
   <param-name>encoding</param-name>
   <param-value>gbk</param-value>
  </init-param>
</filter>
<filter-mapping>
  <filter-name>Set Character Encoding</filter-name>
  <url-pattern>/*</url-pattern>
</filter-mapping>只要是gb2312,gbk,utf8等支持多字节编码的字符集都可以储存汉字，当然，gb2312中的汉字数量远少于gbk，而gb2312,gbk等都可在utf8下编码，这里指定目标编码方式是gbk，重新启动Tomcat后就可以了。
（2）对Get方法提交的表单，由于参数是紧跟在用户的URL请求后面，Tomcat对其的处理方法与Post方法不一样。所以上面设置的过滤器对Get方法没有作用，它需要在其他地方设置。找到Tomca的server.xml配置文件，找到对80（或者是8080等别的，这个是自己修改后的）的Connector组件的设置部分，给这个Connector组件添加一个属性：URIEncoding＝"GBK"。修改后的Connector组件是这样的：

<!-- Define a non-SSL HTTP/1.1 Connector on port 80-->
    <Connector port="80" maxHttpHeaderSize="8192"
               maxThreads="150" minSpareThreads="25" maxSpareThreads="75"
               enableLookups="false" redirectPort="8443" acceptCount="100"
               connectionTimeout="20000" disableUploadTimeout="true"  URIEncoding＝"GBK"/>这样修改后，重启Tomcat就可以正确处理GET方法提交的表单数据了。

    第二个要解决的是数据库存取数据出现的乱码等情况。对于不同的数据库往往支持不同的编码，造成了应用时比较混乱，不同的数据库的解决方法往往是不同的，针对MySql，网上也有各种各样的解决方案，但个人觉得那些太繁了，现在有一个极其简单的解决办法：修改MySql的配置文件，打开MySql安装后的根目录，找到my.init文件，把[mysqld]区的如下语句：default-character-set=latin1修改为：default-character-set=gbk，然后在[client]区增加：default-character-set=gbk，修改后记得做一件事情，到Widows控制面板的管理工具下的服务程序，把Mysql服务停止了重新启动，这样就根本解决了MySql的数据库乱码问题，很简单～～～～