过虑器链FilterChain
当一个web项目中有多个连接器，且这些过虑器对同个url进行过虑。这时就形成了过虑器链/。
在filter的配置当中，有两个配置:filter,filter-mapping.
Filter-mapping在前，则先执行，在后则后执行。
<filter>
<filter-name>first</filter-name>
<filter-class>cn.itcast.filter.FirstFilter</filter-class>
</filter>
<filter>
<filter-name>second</filter-name>
<filter-class>cn.itcast.filter.SecondFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>second</filter-name>
<url-pattern>/four</url-pattern>
</filter-mapping>
<filter-mapping>
<filter-name>first</filter-name>
<url-pattern>/four</url-pattern>
</filter-mapping>
过虑器应用之1-设置request编码
写一个过虑器，对所有url全部过虑，/*.在doFilter方法中，设置request的编码为utf-8。
一般情况下，这个过虑器永远是第一个要执行的过虑器。
最好是通过配置设置编码。<filter><init-param>…
第一步：实现Filter接口，在doFIlter中接收初始化参数，设置编码
package cn.hongxin.filter;
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;
public class CharFilter implements Filter {
//声明编码的成员变量
private String encoding;
public void init(FilterConfig config) throws ServletException {
encoding = config.getInitParameter("bm");
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
request.setCharacterEncoding(encoding);
//放行,必须要放行。
chain.doFilter(request, response);
}
public void destroy() {
}
}
第二步：将上面的类配置到web.xml
<filter>
<filter-name>char</filter-name>
<filter-class>cn.itcast.filter.CharFilter</filter-class>
<init-param>
<!-- 为了便于配置，在配置文件中设置编码 -->
<param-name>bm</param-name>
<param-value>UTF-8</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>char</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
对get可以处理中文
在CharFilter中对reuqest进行包装。
目的：修改增强getParameter方法，如果是get转码。
第一步：声明包装类：
//声明包装类
class MyRequest extends HttpServletRequestWrapper{
public MyRequest(HttpServletRequest request) {
super(request);
}
//增强getParamter
@Override
public String getParameter(String name) {
String val = super.getParameter(name);
if(super.getMethod().equals("GET")){
try {
val = new String(val.getBytes("ISO-8859-1"),super.getCharacterEncoding());
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
}
return val;
}
}
第二步：在doFilter方法中，声明包装类的实例
package cn.hongxin.filter;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
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;
public class CharFilter implements Filter {
// 声明编码的成员变量
private String encoding;
public void init(FilterConfig config) throws ServletException {
encoding = config.getInitParameter("bm");
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
request.setCharacterEncoding(encoding);
response.setContentType("text/html;charset=" + encoding);
// 判断是否需要包装
HttpServletRequest req = (HttpServletRequest) request;
if (req.getMethod().equals("GET")) {
request = new MyRequest(req);
}
// 声明包装类的实例
// 放行
chain.doFilter(request, response);
}
public void destroy() {
}
}
// 声明包装类
class MyRequest extends HttpServletRequestWrapper {
public MyRequest(HttpServletRequest request) {
super(request);
}
// 增强getParamter
@Override
public String getParameter(String name) {
String val = super.getParameter(name);
try {
val = new String(val.getBytes("ISO-8859-1"),
super.getCharacterEncoding());
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
return val;
}
}