(一)編寫一個過濾器改變請求編碼
【步驟1】編寫一個loginform.html文件
<html>
<head>
<title>使用過濾器改變請求編碼</title>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8">
</head>
<body>
<center>
<h2>請輸入用戶名和口令：</h2>
<form method="post" action="servlet/CheckParamServlet">
<table>
<tr>
<td>用戶名：</td>
<td><input name="name" type="text"></td>
</tr>
<tr>
<td>口 令：</td>
<td><input name="pass" type="password"></td>
</tr>
<tr>
<td></td>
<td>
<input name="ok" type="submit" value="提交">
<input name="cancel" type="reset" value="重置">
</td>
</tr>
</table>
</form>
</center>
</body>
</html>
【步驟2】編寫處理請求參數的Servlet
public class CheckParamServlet extends HttpServlet{
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
String name = request.getParameter("name");
String pass = request.getParameter("pass");
response.setContentType("text/html;charset=gb2312");
PrintWriter out = response.getWriter();
out.println("<html><head><title>Param Test</title></head>");
out.println("<h3 align=center>你的用戶名爲："+name+"</h3>");
out.println("<h3 align=center>你的口令爲："+pass+"</h3>");
out.println("</body></html>");
}
public void doPost(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
doGet(request,response);
}
}
【步驟3】修改web.xml文件
<servlet>
<servlet-name>CheckParamServlet</servlet-name>
<servlet-class>CheckParamServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>CheckParamServlet</servlet-name>
<url-pattern>/servlet/check</url-pattern>
</servlet-mapping>
【步驟4】在瀏覽器的地址欄中輸入下面URL：
http://localhost:8080/ helloapp/loginform.html
然後點擊“提交”按鈕，經CheckParamServlet處理後返回的結果如下圖所示：
從這裏我們可以看到，從服務器返回的漢字成了亂碼。原因是沒有指定request的編碼。
下面通過編寫一個過濾器改變請求編碼。
public class EncodingFilter implements Filter {
protected String encoding = null;
protected FilterConfig config;
public void init(FilterConfig filterConfig) throws ServletException {
this.config = filterConfig;
// 得到在web.xml中配置的編碼
this.encoding = filterConfig.getInitParameter("Encoding");
}
public void doFilter(
ServletRequest request,
ServletResponse response,
FilterChain chain)
throws IOException, ServletException {
if (request.getCharacterEncoding() == null) {
// 得到指定的編碼
String encode = getEncoding();
if (encode != null) {
//設置request的編碼
request.setCharacterEncoding(encode);
response.setCharacterEncoding(encode);
}
}
chain.doFilter(request, response);
}
protected String getEncoding() {
return encoding;
}
public void destroy() {
}
}
【步驟6】在web.xml文件中配置過濾器，加入下面代碼：
<filter>
<filter-name>EncodingFilter</filter-name>
<filter-class>filter.EncodingFilter</filter-class>
<init-param>
<param-name>Encoding</param-name>
<param-value>utf-8</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>EncodingFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
【步驟7】重複第（4）步操作，結果如下：
