Tomcat中的Filter

Filter

节选部分源码、源码版本 Tomcat8.5

说明

• filter 是 Servlet 规范

• filter 是在 <请求进入容器后>，执行 Servlet.service方法之前执行

Filter相关接口

public interface Filter {
    // 初始化
    void init(FilterConfig filterConfig) throws ServletException;
    // 过滤器方法
    void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException;
    // 销毁方法
    void destroy();
}

// 过滤器链接口
public interface FilterChain {
    void doFilter(ServletRequest request, ServletResponse response)
            throws IOException, ServletException;
}

• 重点关注：初始化方法、过滤器方法

初始化

// org.apache.catalina.core.StandardContext
@Override
protected synchronized void startInternal() throws LifecycleException {
    // 准备好环境
    if (ok) {
        if (!filterStart()) {
            ok = false;
        }
    }
}

private HashMap<String, ApplicationFilterConfig> filterConfigs =
            new HashMap<>();
public boolean filterStart() {
    // Instantiate and record a FilterConfig for each defined filter
    boolean ok = true;
    synchronized (filterConfigs) {
        filterConfigs.clear();
        // 从 web.xml 解析的 filter 数据中添加到 Map集合中
        for (Entry<String,FilterDef> entry : filterDefs.entrySet()) {
            // <filter-name> 的值
            String name = entry.getKey();
            try {
                // 此处调用 Filter.init 方法，之后保存
                ApplicationFilterConfig filterConfig =
                    new ApplicationFilterConfig(this, entry.getValue());
                filterConfigs.put(name, filterConfig);
            } catch (Throwable t) {
                ok = false;
            }
        }
    }
    return ok;
}

• 在解析完项目后，启动该项目时调用：startInternal 方法
• 调用 filterStart 方法，初始化 Filter，保存 Filter到HashMap中

接收到请求的流程

• 收到请求后根据 请求路径，找到相应的过滤器链，执行 doFilter 方法
• 调用目标方法

// org.apache.catalina.core.StandardWrapperValve
// 节选部分代码
@Override
public final void invoke(Request request, Response response) {
    // 创建执行Filter链
    ApplicationFilterChain filterChain =
        ApplicationFilterFactory.createFilterChain(request, wrapper, servlet);
    // 调用链
    if ((servlet != null) && (filterChain != null)) {
        filterChain.doFilter(request.getRequest(),
                                    response.getResponse());
    }
    // 释放掉 filterChain
    if (filterChain != null) {
        filterChain.release();
    }
}

Line7：ApplicationFilterFactory.createFilterChain

// org.apache.catalina.core.ApplicationFilterFactory
public static ApplicationFilterChain createFilterChain(
    ServletRequest request, Wrapper wrapper, Servlet servlet) {

    // 判断 servlet 是否存在
    if (servlet == null) { return null; }

    ApplicationFilterChain filterChain = null;
    if (request instanceof Request) {
        Request req = (Request) request;
        if (Globals.IS_SECURITY_ENABLED) {
            filterChain = new ApplicationFilterChain();
        } else {
            // 判断 request 是否已经保存
            filterChain = (ApplicationFilterChain) req.getFilterChain();
            if (filterChain == null) {
                filterChain = new ApplicationFilterChain();
                req.setFilterChain(filterChain);
            }
        }
    } else {
        // Request dispatcher in use
        filterChain = new ApplicationFilterChain();
    }

    filterChain.setServlet(servlet);
    filterChain.setServletSupportsAsync(wrapper.isAsyncSupported());

    // 从 Context 中获取所有的  FilterMap 映射信息
    StandardContext context = (StandardContext) wrapper.getParent();
    FilterMap filterMaps[] = context.findFilterMaps();

    // 没有配置 filter，返回 null
    if ((filterMaps == null) || (filterMaps.length == 0))
        return (filterChain);

    // Acquire the information we will need to match filter mappings
    DispatcherType dispatcher =
        (DispatcherType) request.getAttribute(Globals.DISPATCHER_TYPE_ATTR);

    String requestPath = null;
    // 获取请求 路径：index.html
    Object attribute = request.getAttribute(Globals.DISPATCHER_REQUEST_PATH_ATTR);
    if (attribute != null){
        requestPath = attribute.toString();
    }

    String servletName = wrapper.getName();

    for (int i = 0; i < filterMaps.length; i++) {
        if (!matchDispatcher(filterMaps[i] ,dispatcher)) {
            continue;
        }
        // 匹配 url-pattern
        if (!matchFiltersURL(filterMaps[i], requestPath))
            continue;
        // 根据 配置的 filter-name  找到 filterConfig
        ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)
            context.findFilterConfig(filterMaps[i].getFilterName());
        if (filterConfig == null) {
            continue;
        }
        filterChain.addFilter(filterConfig);
    }

    // Add filters that match on servlet name second
    for (int i = 0; i < filterMaps.length; i++) {
        if (!matchDispatcher(filterMaps[i] ,dispatcher)) {
            continue;
        }
        if (!matchFiltersServlet(filterMaps[i], servletName))
            continue;
        ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)
            context.findFilterConfig(filterMaps[i].getFilterName());
        if (filterConfig == null) {
            // FIXME - log configuration problem
            continue;
        }
        filterChain.addFilter(filterConfig);
    }
    return filterChain;
}

LIne10：执行 ApplicationFilterChain.doFilter 方法

public final class ApplicationFilterChain implements FilterChain {
    private int pos = 0;
    private int n = 0;

    @Override
    public void doFilter(ServletRequest request, ServletResponse response)
        throws IOException, ServletException {
        internalDoFilter(request,response);
    }   

    private void internalDoFilter(ServletRequest request, ServletResponse response) {
        // Call the next filter if there is one
        if (pos < n) {
            ApplicationFilterConfig filterConfig = filters[pos++];
            try {
                Filter filter = filterConfig.getFilter();
                if (request.isAsyncSupported() && "false".equalsIgnoreCase(
                    filterConfig.getFilterDef().getAsyncSupported())) {
                    request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR, Boolean.FALSE);
                }
                // 调用具体Filter 的 doFilter 方法。
                filter.doFilter(request, response, this);
            } catch (IOException | ServletException | RuntimeException e) {
                throw e;
            }
            return;
        }

        // 调用servlet实例
        try {
            if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
                lastServicedRequest.set(request);
                lastServicedResponse.set(response);
            }

            if (request.isAsyncSupported() && !servletSupportsAsync) {
                request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR,
                                     Boolean.FALSE);
            }
            servlet.service(request, response);
        } catch (IOException | ServletException | RuntimeException e) {
            throw e;
        } finally {
            if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
                lastServicedRequest.set(null);
                lastServicedResponse.set(null);
            }
        }
    }
}

• Line22，根据链中的具体的 Filter，调用 doFilter 方法
• LIne40，调用 servlet.service(request, response)【此处 与 springmvc 整合入口】

问题

• Request 为什么需要 保存 filterChain

req.setFilterChain(filterChain);

在 StandardWrapperValve 中会释放 filterChain