前言

• spring 4.3.4.RELEASE
• CharacterEncodingFilter ： Spring MVC 提供的字符集过滤器，用于处理项目中的乱码问题
• 项目比较老，大部分url使用的是GBK编码，少量url使用UTF-8编码。
• 需要对 CharacterEncodingFilter 设置例外。即，少量url不要进行 CharacterEncodingFilter 过滤。

CharacterEncodingFilter设置

  <filter>
    <filter-name>characterEncodingFilter</filter-name>
    <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
    <init-param>
      <param-name>encoding</param-name>
      <param-value>GBK</param-value>
    </init-param>
    <init-param>
      <param-name>forceEncoding</param-name>
      <param-value>true</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>characterEncodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

url-pattern很霸气，过滤所有。
forceEncoding更霸气，强制编码格式为GBK。
为什么这么设置不说了（很显然这样让charset为UTF-8的JS很受伤），就说怎么办吧。

受伤的JS

<script type="text/javascript" language="javascript" src="../codebase/laydate/laydate.js"  charset="UTF-8"></script>

CharacterEncodingFilter添加例外

方法1（推荐）：filter-mapping添加例外

嗯~，filter-mapping添加例外是个好办法。

  <!-- 解决编码问题过滤器 -->
  <filter>
    <filter-name>characterEncodingFilter</filter-name>
    <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
    <init-param>
      <param-name>encoding</param-name>
      <param-value>GBK</param-value>
    </init-param>
    <init-param>
      <param-name>forceEncoding</param-name>
      <param-value>true</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>characterEncodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  <!-- CharacterEncodingFilter过滤器添加例外 -->
  <filter>
    <filter-name>characterEncodingFilter_utf8</filter-name>
    <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
    <init-param>
      <param-name>encoding</param-name>
      <param-value>UTF-8</param-value>
    </init-param>
    <init-param>
      <param-name>forceEncoding</param-name>
      <param-value>true</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>characterEncodingFilter_utf8</filter-name>
    <url-pattern>/codebase/laydate/laydate.js</url-pattern>
  </filter-mapping>

方法2：告知CharacterEncodingFilter不用再处理了

根据CharacterEncodingFilter代码显示，在request的Attribute中，增加名为filter-name.FILTERED，值为TRUE的Attribute时，会跳过过滤器。
本文中需要增加名为characterEncodingFilter.FILTERED的Attribute。
增加名为characterEncodingFilter.FILTERED的Attribute的方法则是：在characterEncodingFilter执行前，再增加一个Filter。该Filter向request增加名为characterEncodingFilter.FILTERED的Attribute。（该Filter需要自己写，此处暂不提供）

CharacterEncodingFilter的相关代码如下：

CharacterEncodingFilter的相关代码：

public class CharacterEncodingFilter extends OncePerRequestFilter {
	...
}

OncePerRequestFilter的相关代码：

public abstract class OncePerRequestFilter extends GenericFilterBean {
	/**
	 * Suffix that gets appended to the filter name for the
	 * "already filtered" request attribute.
	 * @see #getAlreadyFilteredAttributeName
	 */
	public static final String ALREADY_FILTERED_SUFFIX = ".FILTERED";
	
	/**
	 * This {@code doFilter} implementation stores a request attribute for
	 * "already filtered", proceeding without filtering again if the
	 * attribute is already there.
	 * @see #getAlreadyFilteredAttributeName
	 * @see #shouldNotFilter
	 * @see #doFilterInternal
	 */
	@Override
	public final void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)
			throws ServletException, IOException {

		if (!(request instanceof HttpServletRequest) || !(response instanceof HttpServletResponse)) {
			throw new ServletException("OncePerRequestFilter just supports HTTP requests");
		}
		HttpServletRequest httpRequest = (HttpServletRequest) request;
		HttpServletResponse httpResponse = (HttpServletResponse) response;

		String alreadyFilteredAttributeName = getAlreadyFilteredAttributeName();
		boolean hasAlreadyFilteredAttribute = request.getAttribute(alreadyFilteredAttributeName) != null;

		if (hasAlreadyFilteredAttribute || skipDispatch(httpRequest) || shouldNotFilter(httpRequest)) {

			// Proceed without invoking this filter...
			filterChain.doFilter(request, response);
		}
		else {
			// Do invoke this filter...
			request.setAttribute(alreadyFilteredAttributeName, Boolean.TRUE);
			try {
				doFilterInternal(httpRequest, httpResponse, filterChain);
			}
			finally {
				// Remove the "already filtered" request attribute for this request.
				request.removeAttribute(alreadyFilteredAttributeName);
			}
		}
	}
	
	/**
	 * Return the name of the request attribute that identifies that a request
	 * is already filtered.
	 * <p>The default implementation takes the configured name of the concrete filter
	 * instance and appends ".FILTERED". If the filter is not fully initialized,
	 * it falls back to its class name.
	 * @see #getFilterName
	 * @see #ALREADY_FILTERED_SUFFIX
	 */
	protected String getAlreadyFilteredAttributeName() {
		String name = getFilterName();
		if (name == null) {
			name = getClass().getName();
		}
		return name + ALREADY_FILTERED_SUFFIX;
	}
	
	...
}

GenericFilterBean的相关代码：

public abstract class GenericFilterBean implements Filter, BeanNameAware, EnvironmentAware,
		EnvironmentCapable, ServletContextAware, InitializingBean, DisposableBean {
	/**
	 * Make the name of this filter available to subclasses.
	 * Analogous to GenericServlet's {@code getServletName()}.
	 * <p>Takes the FilterConfig's filter name by default.
	 * If initialized as bean in a Spring application context,
	 * it falls back to the bean name as defined in the bean factory.
	 * @return the filter name, or {@code null} if none available
	 * @see javax.servlet.GenericServlet#getServletName()
	 * @see javax.servlet.FilterConfig#getFilterName()
	 * @see #setBeanName
	 */
	@Nullable
	protected String getFilterName() {
		return (this.filterConfig != null ? this.filterConfig.getFilterName() : this.beanName);
	}
	...
}