EncodingFilter作用失效的问题（Java Web）

Question

    项目是一个Spring MVC项目，配置了两个filter，配置如下所示：

<!-- 用于字符编码的filter -->
	<filter>
		<filter-name>EncodingFilter</filter-name>
		<filter-class>com.gpl.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>
	
	<!-- 用户身份验证filtera -->
	<filter>
		<filter-name>AuthenticationFilter</filter-name>
		<filter-class>com.gpl.filter.AuthenticationFilter</filter-class>
	</filter>
	<filter-mapping>
		<filter-name>AuthenticationFilter</filter-name>
		<url-pattern>/api/*</url-pattern>
	</filter-mapping>

    两个filter的代码如下所示：

public class EncodingFilter implements Filter{

	private String encodeString = "utf-8";
	
	@Override
	public void destroy() {
		
	}


	@Override
	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain filterChain) throws IOException, ServletException {
		request.setCharacterEncoding(encodeString);
//		response.setCharacterEncoding(encodeString);
		filterChain.doFilter(request, response);
		response.setCharacterEncoding(encodeString);
	}

	@Override
	public void init(FilterConfig arg0) throws ServletException {
		
	}

}

public class AuthenticationFilter implements Filter{

	private String encodeString = "utf-8";

	//	@Resource(name="authenticationService")
	private AuthenticationService authenticationService = new AuthenticationServiceImpl();
	@Override
	public void destroy() {

	}

	@Override
	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain filterChain) throws IOException, ServletException {

		if(authenticationService.isLogin((HttpServletRequest)request)){
			filterChain.doFilter(request, response);
		}else{
			request.setCharacterEncoding(encodeString);
			response.setCharacterEncoding(encodeString);
			response.getWriter().print("请先登录。");
		}

	}

	@Override
	public void init(FilterConfig arg0) throws ServletException {
		// TODO Auto-generated method stub

	}

}

    如果尚未登陆，就会如代码所示，返回字符串“请先登录。”，但是该字符串是乱码，也只有这种情况，返回的中文变成了乱码，EncodingFilter已经设置好字符编码，为什么会这样呢？

    请知道的站友能说说，先谢了。

Answer 1

问题在于，客户端返回的编码不是utf-8编码，实际中，你不能假定客户端编码。应该首先判断request.getCharacterEncoding()是不是null，如果是null，表示客户端没有设置编码，你的编码过滤器应该尝试使用utf-8解析，由于客户端的不确定性，这个情况出现乱码是可以容忍的，没有办法完全解决这个问题。

如果request.getCharacterEncoding()不是null，表示客户端已经设置了编码，你就可以不需要设置编码格式，直接传递给filterChain就可以了。

Spring中解析核心代码如下：

protected void 
doFilterInternal ( HttpServletRequest request
                 , HttpServletResponse response
                 , FilterChain filterChain
                 )
throws ServletException
     , IOException
{
  if (    this.encoding != null 
       && (   this.forceEncoding 
           || request.getCharacterEncoding() == null
          )
     )
  {
    request.setCharacterEncoding(this.encoding);
    if (this.forceEncoding) {
      response.setCharacterEncoding(this.encoding);
    }
  }
  filterChain.doFilter(request, response);
}

this.encoding相当于你代码中的保存"utf-8"的变量，this.forceEncoding则表示是否需要强制按照指定编码解析请求和设置响应的编码。