CAT源码分析之过滤器

在 CAT 的 web.xml 中配置的2个过滤器

<filter>
    <filter-name>cat-filter</filter-name>
    <filter-class>com.dianping.cat.servlet.CatFilter</filter-class>
</filter>
<filter>
    <filter-name>domain-filter</filter-name>
    <filter-class>com.dianping.cat.report.view.DomainFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>cat-filter</filter-name>
    <url-pattern>/r/*</url-pattern>
    <dispatcher>REQUEST</dispatcher>
</filter-mapping>
<filter-mapping>
    <filter-name>domain-filter</filter-name>
    <url-pattern>/r/*</url-pattern>
    <dispatcher>REQUEST</dispatcher>
</filter-mapping>
<filter-mapping>
    <filter-name>cat-filter</filter-name>
    <url-pattern>/s/*</url-pattern>
    <dispatcher>REQUEST</dispatcher>
</filter-mapping>
<filter-mapping>
    <filter-name>cat-filter</filter-name>
    <url-pattern>/jsp/*</url-pattern>
    <dispatcher>FORWARD</dispatcher>
</filter-mapping>

其中

• domain-filter 根据 domain 设置 cookie 有效期
  • 只针对报表请求， url-pattern 是 /r/*
• cat-filter 处理 请求信息

---

值得学习点

• 枚举实现接口和循环操作

  
  package com.dianping.cat.servlet;
  
  public class CatFilter implements Filter {
  
      private List<Handler> m_handlers = new ArrayList<Handler>();
  
      @Override
  
      public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException,
  
              ServletException {
  
          Context ctx = new Context((HttpServletRequest) request, (HttpServletResponse) response, chain, m_handlers);
  
          ctx.handle(); // for 循环即 分步处理
  
      }
  
     ....
  
      @Override
  
      public void init(FilterConfig filterConfig) throws ServletException {
  
          // 处理化 分步步骤
  
          m_handlers.add(CatHandler.ENVIRONMENT);
  
          m_handlers.add(CatHandler.LOG_SPAN);
  
          m_handlers.add(CatHandler.LOG_CLIENT_PAYLOAD);
  
          m_handlers.add(CatHandler.ID_SETUP);
  
      }
  
      // 枚举 实现接口
  
      private static enum CatHandler implements Handler {
  
          ENVIRONMENT {
  
              @Override
  
              public void handle(Context ctx) throws IOException, ServletException {
  
                  HttpServletRequest req = ctx.getRequest();
  
                  boolean top = !Cat.getManager().hasContext();
  
                  ctx.setTop(top);
  
                  if (top) {
  
                      ctx.setType(CatConstants.TYPE_URL);
  
                      setTraceMode(req);
  
                  } else {
  
                      ctx.setType(CatConstants.TYPE_URL_FORWARD);
  
                  }
  
                  ctx.handle();
  
              }
  
             ....
  
          },
  
          ID_SETUP {
  
              ....
  
              @Override
  
              public void handle(Context ctx) throws IOException, ServletException {
  
                  boolean isTraceMode = Cat.getManager().isTraceMode();
  
                  HttpServletResponse res = ctx.getResponse();
  
                  if (isTraceMode) {
  
                      String id = Cat.getCurrentMessageId();
  
                      res.setHeader("X-CAT-ROOT-ID", id);
  
                      res.setHeader("X-CAT-SERVER", getCatServer());
  
                  }
  
                  ctx.handle();
  
              }
  
          },
  
          LOG_CLIENT_PAYLOAD {
  
              @Override
  
              public void handle(Context ctx) throws IOException, ServletException {
  
                  HttpServletRequest req = ctx.getRequest();
  
                  String type = ctx.getType();
  
                  if (ctx.isTop()) {
  
                      logRequestClientInfo(req, type);
  
                      logRequestPayload(req, type);
  
                  } else {
  
                      logRequestPayload(req, type);
  
                  }
  
                  ctx.handle();
  
              }
  
              ....
  
         },
  
          LOG_SPAN {
  
             .....
  
              @Override
  
              public void handle(Context ctx) throws IOException, ServletException {
  
                  HttpServletRequest req = ctx.getRequest();
  
                  Transaction t = Cat.newTransaction(ctx.getType(), getRequestURI(req));
  
                  try {
  
                      ctx.handle();
  
                      customizeStatus(t, req);
  
                  } catch (ServletException e) {
  
                      t.setStatus(e);
  
                      Cat.logError(e);
  
                      throw e;
  
                  } catch (IOException e) {
  
                      t.setStatus(e);
  
                      Cat.logError(e);
  
                      throw e;
  
                  } catch (Throwable e) {
  
                      t.setStatus(e);
  
                      Cat.logError(e);
  
                      throw new RuntimeException(e);
  
                  } finally {
  
                      customizeUri(t, req);
  
                      t.complete();
  
                  }
  
              }
  
          ....
  
          };
  
      }
  
      protected static class Context {
  
          private FilterChain m_chain;
  
          private List<Handler> m_handlers;
  
          private int m_index;
  
          private HttpServletRequest m_request;
  
          private HttpServletResponse m_response;
  
          private boolean m_top;
  
          private String m_type;
  
          public Context(HttpServletRequest request, HttpServletResponse response, FilterChain chain, List<Handler> handlers) {
  
              m_request = request;
  
              m_response = response;
  
              m_chain = chain;
  
              m_handlers = handlers;
  
          }
  
          ....
  
          // Context 封装 Handler 逻辑
  
          public void handle() throws IOException, ServletException {
  
              if (m_index < m_handlers.size()) {
  
                  Handler handler = m_handlers.get(m_index++);
  
                  handler.handle(this);
  
              } else {
  
                  m_chain.doFilter(m_request, m_response);
  
              }
  
          }
  
          ....
  
      }
  
      // Handler 接口定义
  
      protected static interface Handler {
  
          public void handle(Context ctx) throws IOException, ServletException;
  
      }
  
  }