HttpServletRequestWrapper两个类学习总结（有关中文乱码的例子）

在学习javax.servlet.http包中发现两个类：
HttpServeltRequestWrapper
HttpServletResponseWrapper:
这两个类的方法跟HttpServletRequest/HttpServletResponse的方法基本相同。
可以理解为这两个类是包装类。
可以按照业务需求重写里面的方法，然后将request/response进行包装后，满足具体功能。
实际用例：
过滤中文参数乱码。
具体思路是：
建立filter过滤器和自定义包装类。
在filter过滤的时候对request和response进行过滤和包装，起到让乱码转换成中文的功能。
代码如下：

package demo.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;
import javax.servlet.http.HttpServletRequest;

import demo.wrapper.MyHttpServletRequestWrapper;

public class ContentTypeFilter implements Filter {

	private String charset = "UTF-8";
	private FilterConfig config;

	@Override
	public void destroy() {
		// TODO Auto-generated method stub
		System.out.println(config.getFilterName() + "被销毁");
		charset = null;
		config = null;

	}

	@Override
	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		// TODO Auto-generated method stub
		request.setCharacterEncoding(charset);
		response.setCharacterEncoding(charset);
		//response.setContentType("text/html;charset=UTF-8");
		HttpServletRequest req = (HttpServletRequest) request;
		if (req.getMethod().equalsIgnoreCase("get")) {

			req = new MyHttpServletRequestWrapper(req, charset);
		}
		System.out.println("----请求被" + config.getFilterName() + "过滤");
		chain.doFilter(req, response);
		System.out.println("----相应" + config.getFilterName() + "过滤");
	}

	@Override
	public void init(FilterConfig config) throws ServletException {
		// TODO Auto-generated method stub
		this.config = config;
		String charset = config.getServletContext().getInitParameter("charset");
		if (charset != null && charset.trim().length() != 0) {
			this.charset = charset;
		}

	}

}

package demo.wrapper;

import java.io.UnsupportedEncodingException;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

public class MyHttpServletRequestWrapper extends HttpServletRequestWrapper {

	private String charset = "UTF-8";

	public MyHttpServletRequestWrapper(HttpServletRequest request) {
		super(request);
		// TODO Auto-generated constructor stub
	}

	public MyHttpServletRequestWrapper(HttpServletRequest request,
			String charset) {
		super(request);
		this.charset = charset;
	}

	@Override
	public String getParameter(String name) {
		String value = super.getParameter(name);
		value = value == null ? null : convert(value); 
		return value;
	}

	private String convert(String value) {
		System.out.println("编码转换之前：" + value);
		try {
			return new String(value.trim().getBytes("ISO-8859-1"), charset);
		} catch (UnsupportedEncodingException e) {
			// TODO Auto-generated catch block
			System.out.println("转换失败");
			return value;
		}

	}
}

        <filter>
		<filter-name>ContentTypeFilter</filter-name>
		<filter-class>demo.filter.ContentTypeFilter</filter-class>
	</filter>
	<filter-mapping>
		<filter-name>ContentTypeFilter</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>

在完成小例子的时候 要到一个bug就是一直显示乱码。找了半天才发现。
我的包装类的功能实现了。
但是因为没有给jsp和response的ContentType设置utf-8导致的。
response.setContentType("text/html;charset=UTF-8");