Filter

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 2019/04/23   Share

Filter

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

接口

package javax.servlet;
public interface FilterChain {
    void doFilter(ServletRequest request, ServletResponse response)
            throws IOException, ServletException;
}

实现

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 {
		// 判断是否开启安全管理器
        if( Globals.IS_SECURITY_ENABLED ) {
            final ServletRequest req = request;
            final ServletResponse res = response;
            try {
                java.security.AccessController.doPrivileged(
                    new java.security.PrivilegedExceptionAction<Void>() {
                        @Override
                        public Void run()
                            throws ServletException, IOException {
                            internalDoFilter(req,res);
                            return null;
                        }
                    }
                );
            } catch( PrivilegedActionException pe) {
                throw new ServletException(e.getMessage(), e);
            }
        } else {
            internalDoFilter(request,response);
        }
    }   
    
    private void internalDoFilter(ServletRequest request,
                                  ServletResponse response)
        throws IOException, ServletException {

        // 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);
                }
                if( Globals.IS_SECURITY_ENABLED ) {
                    final ServletRequest req = request;
                    final ServletResponse res = response;
                    Principal principal =
                        ((HttpServletRequest) req).getUserPrincipal();

                    Object[] args = new Object[]{req, res, this};
                    SecurityUtil.doAsPrivilege ("doFilter", filter, 
                                                classType, args, principal);
                } else {
                    // 调用具体Filter 的 doFilter 方法。
                    filter.doFilter(request, response, this);
                }
            } catch (IOException | ServletException | RuntimeException e) {
                throw e;
            } catch (Throwable e) {
                throw new ServletException(sm.getString("filterChain.filter"), 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);
            }
            // Use potentially wrapped request from this point
            if ((request instanceof HttpServletRequest) &&
                    (response instanceof HttpServletResponse) &&
                    Globals.IS_SECURITY_ENABLED ) {
                final ServletRequest req = request;
                final ServletResponse res = response;
                Principal principal =
                    ((HttpServletRequest) req).getUserPrincipal();
                Object[] args = new Object[]{req, res};
                SecurityUtil.doAsPrivilege("service",
                                           servlet,
                                           classTypeUsedInService,
                                           args,
                                           principal);
            } else {
                servlet.service(request, response);
            }
        } catch (IOException | ServletException | RuntimeException e) {
            throw e;
        } catch (Throwable e) {
            throw new ServletException(sm.getString("filterChain.servlet"), e);
        } finally {
            if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
                lastServicedRequest.set(null);
                lastServicedResponse.set(null);
            }
        }
    }
}

Line：63

// 列如：CorsFilter
@Override
public void doFilter(final ServletRequest servletRequest,
                     final ServletResponse servletResponse, 
                     final FilterChain filterChain) {
    switch (requestType) {
        case SIMPLE:
            // Handles a Simple CORS request.
            this.handleSimpleCORS(request, response, filterChain);
            break;
        case ACTUAL:
            // Handles an Actual CORS request.
            this.handleSimpleCORS(request, response, filterChain);
            break;
        default:
            // Handles a CORS request that violates specification.
            this.handleInvalidCORS(request, response, filterChain);
            break;
    }
}

private void handleNonCORS(final HttpServletRequest request,
                           final HttpServletResponse response, 
                           final FilterChain filterChain) {

    addStandardHeaders(request, response);
    // 调用下一个 Filter，回到 ApplicationFilterChain.doFilter
    filterChain.doFilter(request, response);
}

LIne101：servlet.service(request, response);

1	// 调用 DispatcherServlet.service方法

Filter注入

// org.apache.catalina.core.StandardContext
@Override
protected synchronized void startInternal() throws LifecycleException {
    // 准备好环境
    // Configure and call application filters
    if (ok) {
        if (!filterStart()) {
            log.error(sm.getString("standardContext.filterFail"));
            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()) {
            String name = entry.getKey();
            try {
                ApplicationFilterConfig filterConfig =
                    new ApplicationFilterConfig(this, entry.getValue());
                filterConfigs.put(name, filterConfig);
            } catch (Throwable t) {
                ok = false;
            }
        }
    }
    return ok;
}

调用流程

在收到请求后，执行 Pipeline，走到 StandardWrapperValve

// org.apache.catalina.core.StandardWrapperValve
@Override
public final void invoke(Request request, Response response) {
    // Create the filter chain for this request
    ApplicationFilterChain filterChain =
        ApplicationFilterFactory.createFilterChain(request, wrapper, servlet);
}

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

    // If there is no servlet to execute, return null
    if (servlet == null)
        return null;

    // Create and initialize a filter chain object
    ApplicationFilterChain filterChain = null;
    if (request instanceof Request) {
        Request req = (Request) request;
        if (Globals.IS_SECURITY_ENABLED) {
            // Security: Do not recycle
            filterChain = new ApplicationFilterChain();
        } else {
            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();

    // Add the relevant path-mapped filters to this filter chain
    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;
}

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