Filter接口中有三个重要的方法。 （java类要实现的接口）
- init()方法：初始化参数，在创建Filter时自动调用。当我们需要设置初始化参数的时候，可以写到该方法中。
- doFilter()方法：拦截到要执行的请求时，doFilter就会执行。
- destroy()方法：在销毁Filter时自动调用。
web.xml配置
<filter>
<filter-name>encodingFilter</filter-name>
<filter-class>包点EncodingFilter</filter-class>
<init-param>
<param-name>encoding</param-name>
<param-value>UTF-8</param-value>
</init-param>
<init-param>
<param-name>contentType</param-name>
<param-value>text/html;charset=UTF-8</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>encodingFilter</filter-name>
<url-pattern>*.ht</url-pattern>
</filter-mapping>
<filter-mapping>
<filter-name>encodingFilter</filter-name>
<url-pattern>/servlet/ValidJs</url-pattern>
</filter-mapping>
java代码
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.http.HttpServletResponse;
/**
* 编码过滤器， 设置当前系统的编码。
*
* @author crd
*
*/
public class EncodingFilter implements Filter
{
private String encoding = "UTF-8";
private String contentType = "text/html;charset=UTF-8";
@Override
public void destroy()
{
}
@Override
public void doFilter(ServletRequest request, ServletResponse httpresponse,
FilterChain chain) throws IOException, ServletException
{
HttpServletResponse response=(HttpServletResponse)httpresponse;
request.setCharacterEncoding(encoding);
response.setCharacterEncoding(encoding);
response.setContentType(contentType);
response.setHeader("Cache-Control", "no-cache");
response.setHeader("Pragma", "no-cache");
response.setDateHeader("Expires", -1);
chain.doFilter(request, response);
}
@Override
public void init(FilterConfig config) throws ServletException
{
String _encoding = config.getInitParameter("encoding");
String _contentType = config.getInitParameter("contentType");
// String ext=config.getInitParameter("ext");
if (_encoding != null)
encoding = _encoding;
if (_contentType != null)
contentType = _contentType;
}
}