使用过滤器对所有请求进行字符编码过滤_过滤器如何实现响应字符集的统一过滤?

##过滤器Filter
A filter is an object that performs filtering tasks on either the request to a resource (a servlet or static content), or on the response from a resource, or both.

过滤器对访问资源的请求或服务器的响应进行过滤

Filters perform filtering in the doFilter method.

在doFilter()方法中进行过滤

Filters are configured in the deployment descriptor of a web application

过滤器必须在配置文件web.xml中进行配置

##字符过滤器的代码实现

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.Enumeration;

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;

public class CharacterEncodingFilter implements Filter{

	protected String encoding = null;
	protected FilterConfig filterConfig = null;
	protected boolean ignore = true;  //是否忽视指定的字符集 默认为true
	@Override
	public void destroy() {
		this.encoding = null;
		this.filterConfig = null;
	}

	void encoding(HttpServletRequest request){
		Enumeration<?> names = request.getParameterNames();
		while(names.hasMoreElements()){
			String[] values = request.getParameterValues(names.nextElement().toString());
			for(int i = 0; i < values.length; i++){
				try {
					values[i] = new String(values[i].getBytes("iso-8859-1"),encoding);
				} catch (UnsupportedEncodingException e) {
					e.printStackTrace();
				}
			}
		}
	}
	@Override
	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		if(ignore || (request.getCharacterEncoding() == null)){
			String encoding = selectEncoding(request);
			if(encoding != null){
				request.setCharacterEncoding(encoding);
			}
			HttpServletRequest req = (HttpServletRequest) request;
			if(req.getMethod().equalsIgnoreCase("get")){
				encoding(req);
			}
		}
		chain.doFilter(request, response);
	}

	private String selectEncoding(ServletRequest request) {
		return (this.encoding);
	}

	@Override
	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;
	}

}
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##配置

<filter>
    <filter-name>CharacterEncodingFilter</filter-name>
    <filter-class>com.icss.filter.CharacterEncodingFilter</filter-class>
    <init-param>
        <param-name>encoding</param-name>
        <param-value>UTF-8</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>CharacterEncodingFilter</filter-name>
    <url-pattern>/*</url-pattern> <!-- 对所有请求进行过滤 -->
  </filter-mapping>
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