Filter的用法

public interface Filter {
    //初始化方法，整个生命周期中只执行一次。
    //在init方法成功(失败如抛异常等)执行完前，不能提供过滤服务。
    //参数FilterConfig用于获取初始化参数
    public void init(FilterConfig filterConfig) throws ServletException;

    //执行过滤任务的方法，参数FilterChain表示过滤器链，doFilter方法中只有执行chain.doFilter()后才能调用下一个过滤器的doFilter方法
    //才能将请求交经下一个Filter或Servlet执行
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException;

    //销毁方法，当移出服务时由web容器调用。整个生命周期中destroy方法只会执行一次
    //destroy方法可用于释放持有的资源，如内存、文件句柄等
    public void destroy();
}

• Filter的接口定义包含init、doFilter、destroy等接口。

@Component
public class TimeFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("time filter init");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("time filter start");
        long startTime = System.currentTimeMillis();

        filterChain.doFilter(servletRequest, servletResponse);

        long endTime = System.currentTimeMillis();
        System.out.println("time filter consume " + (endTime - startTime) + " ms");
        System.out.println("time filter end");
    }

    @Override
    public void destroy() {
        System.out.println("time filter init");
    }
}

• 自定义 Filter对象需要实现Filter的接口并实现其中的方法。

Filter的初始化

public class StandardContext extends ContainerBase
        implements Context, NotificationEmitter {

    private HashMap<String, FilterDef> filterDefs = new HashMap<>();
    private HashMap<String, ApplicationFilterConfig> filterConfigs = new HashMap<>();

    @Override
    protected synchronized void startInternal() throws LifecycleException {
            // 省略其他代码
            if (ok) {
                if (!filterStart()) {
                    log.error(sm.getString("standardContext.filterFail"));
                    ok = false;
                }
            }
    }

    public boolean filterStart() {
        boolean ok = true;
        synchronized (filterConfigs) {
            filterConfigs.clear();
            // 遍历filterDefs的map初始化Filter对象
            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;
    }
}

• StandardContext#filterStart负责遍历filterDefs并创建ApplicationFilterConfig对象。
• ApplicationFilterConfig是包含 Filter 实例的对象，FilterDef是包含的过滤器的定义。
• StandardContext的filterDefs保存 Filter 的定义，filterConfigs保存 Filter 的实例包装对象ApplicationFilterConfig。

Filter核心类定义

public class FilterDef implements Serializable {

    private static final long serialVersionUID = 1L;
    private static final StringManager sm = StringManager.getManager(Constants.PACKAGE_NAME);

    private String description = null;
    private String displayName = null;
    private transient Filter filter = null;
    private String filterClass = null;
    private String filterName = null;
    private String largeIcon = null;
    private final Map<String, String> parameters = new HashMap<>();
    private String smallIcon = null;
    private String asyncSupported = null;
}

• FilterDef是Filter的定义类，filterClass表示过滤器的定义类。

public final class ApplicationFilterConfig implements FilterConfig, Serializable {

    private static final long serialVersionUID = 1L;
    static final StringManager sm = StringManager.getManager(Constants.Package);
    private static final List<String> emptyString = Collections.emptyList();
    private final transient Context context;
    private transient Filter filter = null;
    private final FilterDef filterDef;
    private transient InstanceManager instanceManager;
    private ObjectName oname;

    ApplicationFilterConfig(Context context, FilterDef filterDef)
            throws ClassCastException, ClassNotFoundException, IllegalAccessException,
            InstantiationException, ServletException, InvocationTargetException, NamingException,
            IllegalArgumentException, NoSuchMethodException, SecurityException {

        super();

        this.context = context;
        this.filterDef = filterDef;
        if (filterDef.getFilter() == null) {
            getFilter();
        } else {
            this.filter = filterDef.getFilter();
            getInstanceManager().newInstance(filter);
            initFilter();
        }
    }

    Filter getFilter() throws ClassCastException, ClassNotFoundException, IllegalAccessException,
            InstantiationException, ServletException, InvocationTargetException, NamingException,
            IllegalArgumentException, NoSuchMethodException, SecurityException {

        if (this.filter != null)
            return (this.filter);

        // 创建 并初始化 Filter 对象
        String filterClass = filterDef.getFilterClass();
        this.filter = (Filter) getInstanceManager().newInstance(filterClass);
        initFilter();

        return (this.filter);
    }


    private void initFilter() throws ServletException {
        if (context instanceof StandardContext &&
                context.getSwallowOutput()) {
            try {
                SystemLogHandler.startCapture();
                filter.init(this);
            } finally {
                String capturedlog = SystemLogHandler.stopCapture();
                if (capturedlog != null && capturedlog.length() > 0) {
                    getServletContext().log(capturedlog);
                }
            }
        } else {
            filter.init(this);
        }

        registerJMX();
    }
}

• ApplicationFilterConfig的创建过程就是通过实例化FilterDef的 filterClass的类并调用 Filter 的 init 方法初始化 Filter 对象。
• initFilter方法负责初始化 Filter 对象，也就是调用 filter 的 init 方法。
• ApplicationFilterConfig的filter字段保存实例话后的 Filter 实例。

FilterDef的加载

FilterDef 的来源需要如果是 web.xml 定义那么就从 webxml 中获取，如果是springboot 工程，就通过ApplicationContextFacade类型进行获取。

public class ContextConfig implements LifecycleListener {

    private void configureContext(WebXml webxml) {
        // 省略相关代码
        for (FilterDef filter : webxml.getFilters().values()) {
            if (filter.getAsyncSupported() == null) {
                filter.setAsyncSupported("false");
            }
            context.addFilterDef(filter);
        }
    }
}

• 通过webxml.getFilters()获取过滤器的FilterDef并添加到StandardContext对象当中。
• 上述方式一般在 spring MVC 项目在 web.xml 配置过滤器的时候使用。

public class ApplicationContextFacade implements org.apache.catalina.servlet4preview.ServletContext {

    @Override
    public FilterRegistration.Dynamic addFilter(String filterName,
            Filter filter) {
        if (SecurityUtil.isPackageProtectionEnabled()) {
            return (FilterRegistration.Dynamic) doPrivileged("addFilter",
                    new Class[]{String.class, Filter.class},
                    new Object[]{filterName, filter});
        } else {
            return context.addFilter(filterName, filter);
        }
    }
}


public class ApplicationContext implements org.apache.catalina.servlet4preview.ServletContext {

    private FilterRegistration.Dynamic addFilter(String filterName,
            String filterClass, Filter filter) throws IllegalStateException {

        FilterDef filterDef = context.findFilterDef(filterName);
        // context是StandardContext对象
        if (filterDef == null) {
            filterDef = new FilterDef();
            filterDef.setFilterName(filterName);
            context.addFilterDef(filterDef);
        } else {
            if (filterDef.getFilterName() != null &&
                    filterDef.getFilterClass() != null) {
                return null;
            }
        }

        if (filter == null) {
            filterDef.setFilterClass(filterClass);
        } else {
            filterDef.setFilterClass(filter.getClass().getName());
            filterDef.setFilter(filter);
        }

        return new ApplicationFilterRegistration(filterDef, context);
    }
}

• 通过ApplicationContextFacade的addFilter方法并最终调用ApplicationContext的addFilter方法将过滤器的FilterDef并添加到StandardContext对象当中。
• 是上述方式一般在springboot 工程中的加载过程。

Filter的加载流程

• Filter的定义的加载顺序如上图所示，包括解析 web.xml 文件生成 FilterDef并保存到 StandardContext 当中，遍历 StandardContext 的 FilterDef 生成ApplicationFilterConfig并保存到StandardContext当中。
• StandardContext负责保存核心的FilterDef和ApplicationFilterConfig。

Filter执行

Filter整体流程

final class StandardWrapperValve
    extends ValveBase {

    @Override
    public final void invoke(Request request, Response response)
        throws IOException, ServletException {

        // 省略相关代码
        ApplicationFilterChain filterChain =
                ApplicationFilterFactory.createFilterChain(request, wrapper, servlet);

        try {
            if ((servlet != null) && (filterChain != null)) {
                if (context.getSwallowOutput()) {
                    try {
                        SystemLogHandler.startCapture();
                        if (request.isAsyncDispatching()) {
                            request.getAsyncContextInternal().doInternalDispatch();
                        } else {
                            filterChain.doFilter(request.getRequest(),
                                    response.getResponse());
                        }
                    } finally {
                    }
                } else {
                    if (request.isAsyncDispatching()) {
                        request.getAsyncContextInternal().doInternalDispatch();
                    } else {
                        filterChain.doFilter
                            (request.getRequest(), response.getResponse());
                    }
                }

            }
        } catch (Throwable e) {

        }

        // Release the filter chain (if any) for this request
        if (filterChain != null) {
            filterChain.release();
        }
    }
}

• Filter 执行流程在StandardWrapperValve#invoke 方法当中，核心流程包括创建 Filter 调用链和执行 Filter 调用链。
• ApplicationFilterFactory.createFilterChain负责创建调用链对象ApplicationFilterChain。
• filterChain.doFilter负责执行 Filter 调用链。

filterChain的构建

public final class ApplicationFilterChain implements FilterChain {
    public static final int INCREMENT = 10;
    private ApplicationFilterConfig[] filters = new ApplicationFilterConfig[0];
    private int pos = 0;
    private int n = 0;
    private Servlet servlet = null;
    private boolean servletSupportsAsync = false;
    private static final StringManager sm = StringManager.getManager(Constants.Package);

    void addFilter(ApplicationFilterConfig filterConfig) {
        for(ApplicationFilterConfig filter:filters)
            if(filter==filterConfig)
                return;

        if (n == filters.length) {
            ApplicationFilterConfig[] newFilters =
                new ApplicationFilterConfig[n + INCREMENT];
            System.arraycopy(filters, 0, newFilters, 0, n);
            filters = newFilters;
        }
        filters[n++] = filterConfig;
    }
}

• ApplicationFilterChain的内部维护ApplicationFilterConfig[] filters来保存 Filter 对象。

public final class ApplicationFilterFactory {

    public static ApplicationFilterChain createFilterChain(ServletRequest request,
            Wrapper wrapper, Servlet servlet) {

        ApplicationFilterChain filterChain = null;
        if (request instanceof Request) {
            Request req = (Request) request;
            if (Globals.IS_SECURITY_ENABLED) {
                filterChain = new ApplicationFilterChain();
            } else {
                filterChain = (ApplicationFilterChain) req.getFilterChain();
                if (filterChain == null) {
                    filterChain = new ApplicationFilterChain();
                    req.setFilterChain(filterChain);
                }
            }
        } else {
            filterChain = new ApplicationFilterChain();
        }

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

        // 通过StandardContext#findFilterMaps获取所有的Filter对象
        StandardContext context = (StandardContext) wrapper.getParent();
        FilterMap filterMaps[] = context.findFilterMaps();

        if ((filterMaps == null) || (filterMaps.length == 0))
            return (filterChain);

        DispatcherType dispatcher =
                (DispatcherType) request.getAttribute(Globals.DISPATCHER_TYPE_ATTR);

        String requestPath = null;
        Object attribute = request.getAttribute(Globals.DISPATCHER_REQUEST_PATH_ATTR);
        if (attribute != null){
            requestPath = attribute.toString();
        }

        String servletName = wrapper.getName();

        // 匹配路径  Add the relevant path-mapped filters to this filter chain
        for (int i = 0; i < filterMaps.length; i++) {
            if (!matchDispatcher(filterMaps[i] ,dispatcher)) {
                continue;
            }
            if (!matchFiltersURL(filterMaps[i], requestPath))
                continue;

            // 通过StandardContext#findFilterConfig获取Filter对象
            ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)
                context.findFilterConfig(filterMaps[i].getFilterName());
            if (filterConfig == null) {
                continue;
            }
            filterChain.addFilter(filterConfig);
        }

        // 匹配servlet的名字 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 the completed filter chain
        return filterChain;
    }
}

• 获取StandardContext的FilterMap[] 对象，遍历FilterMap[]后进行规则匹配，匹配后通过 StandardContext 获取ApplicationFilterConfig对象添加到ApplicationFilterChain当中。
• StandardContext本身维护的ApplicationFilterConfig的加载流程已经分析，需要了解FilterMap的加载过程。

Filter 执行流程

public final class ApplicationFilterChain implements FilterChain {

    public static final int INCREMENT = 10;
    private ApplicationFilterConfig[] filters = new ApplicationFilterConfig[0];
    private int pos = 0;
    private int n = 0;
    private Servlet servlet = null;
    private boolean servletSupportsAsync = false;
    private static final StringManager sm = StringManager.getManager(Constants.Package);


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

        if( Globals.IS_SECURITY_ENABLED ) {
            // 省略相关代码
        } else {
            internalDoFilter(request,response);
        }
    }

    private void internalDoFilter(ServletRequest request,
                                  ServletResponse response)
        throws IOException, ServletException {

        if (pos < n) {
            ApplicationFilterConfig filterConfig = filters[pos++];
            try {
                Filter filter = filterConfig.getFilter();

                if( Globals.IS_SECURITY_ENABLED ) {
                    // 省略相关代码
                } else {
                    filter.doFilter(request, response, this);
                }
            } catch (IOException | ServletException | RuntimeException e) {

            } catch (Throwable e) {

            }
            return;
        }

        try {
            if ((request instanceof HttpServletRequest) &&
                    (response instanceof HttpServletResponse) &&
                    Globals.IS_SECURITY_ENABLED ) {
                // 省略相关代码
            } else {
                servlet.service(request, response);
            }
        } catch (IOException | ServletException | RuntimeException e) {

        } catch (Throwable e) {

        } finally {

        }
    }
}

• ApplicationFilterChain#internalDoFilter负责 Filter 调用链的执行，内部通过维护 Filter 的对象数组filters和下标pos依次执行 Filter。

FilterMap介绍

/**
 * 来看下这个类的官方解释：
 * Web应用程序的过滤器映射的表示形式，如部署描述符中<filter-mapping>元素中的所示
 * 每个过滤器映射都必须包含过滤器名称以及URL模式或servlet名称
 * 例如以下配置：
 * <filter-mapping>  
 *    <filter-name>MyFilter</filter-name>  
 *    <url-pattern>/my</url-pattern> 
 * </filter-mapping> 
 * 
 * 说白了，这个FilterMap就是封装了配置信息中<filter-mapping>标签中的元素
 * 其中还包含了两个重点属性：过滤器名、过滤器对应过滤的url
 */
public class FilterMap extends XmlEncodingBase implements Serializable {
    private boolean matchAllUrlPatterns = false;
    private boolean matchAllServletNames = false;

    // serverlet的名字，对应多个
    private String[] servletNames = new String[0];
    // 过滤器名，对应的是<filter-name>中的内容
    private String filterName = null; 
    // 过滤url，对应的是<url-pattern>中的内容（可配置多个<filter-mapping>匹配不同的url，因此是数组形式）
    private String[] urlPatterns = new String[0]; 
}

• FilterMap的核心字段包括匹配的 Url格式，对应的 Filter 对象的filterName等。

FilterMap的加载

public class ContextConfig implements LifecycleListener {

    private void configureContext(WebXml webxml) {
        // 省略相关代码

        for (FilterMap filterMap : webxml.getFilterMappings()) {
            context.addFilterMap(filterMap);
        }
    }
}

• 通过webxml.getFilterMappings()获取过滤器的filterMap并添加到StandardContext中。
• 上述方式一般在 spring MVC 项目在 web.xml 配置过滤器的时候使用。

public class ApplicationFilterRegistration
        implements FilterRegistration.Dynamic {

    private static final StringManager sm =
      StringManager.getManager(Constants.Package);

    private final FilterDef filterDef;
    private final Context context;

    public ApplicationFilterRegistration(FilterDef filterDef,
            Context context) {
        this.filterDef = filterDef;
        this.context = context;
    }

    @Override
    public void addMappingForServletNames(
            EnumSet<DispatcherType> dispatcherTypes, boolean isMatchAfter,
            String... servletNames) {

        FilterMap filterMap = new FilterMap();
        filterMap.setFilterName(filterDef.getFilterName());

        if (dispatcherTypes != null) {
            for (DispatcherType dispatcherType : dispatcherTypes) {
                filterMap.setDispatcher(dispatcherType.name());
            }
        }

        if (servletNames != null) {
            for (String servletName : servletNames) {
                filterMap.addServletName(servletName);
            }

            if (isMatchAfter) {
                context.addFilterMap(filterMap);
            } else {
                context.addFilterMapBefore(filterMap);
            }
        }
    }

    @Override
    public void addMappingForUrlPatterns(
            EnumSet<DispatcherType> dispatcherTypes, boolean isMatchAfter,
            String... urlPatterns) {

        FilterMap filterMap = new FilterMap();
        filterMap.setFilterName(filterDef.getFilterName());

        if (dispatcherTypes != null) {
            for (DispatcherType dispatcherType : dispatcherTypes) {
                filterMap.setDispatcher(dispatcherType.name());
            }
        }

        if (urlPatterns != null) {
            for (String urlPattern : urlPatterns) {
                filterMap.addURLPattern(urlPattern);
            }

            if (isMatchAfter) {
                context.addFilterMap(filterMap);
            } else {
                context.addFilterMapBefore(filterMap);
            }
        }
    }
}

• addMappingForServletNames和addMappingForUrlPatterns负责获取过滤器的filterMap并添加到StandardContext中。
• 上述方式一般在 spring boot 工程中加载FilterMap使用。

Filter执行流程图

• 通过解析 web.xml 文件生成 FilterMap并保存到 StandardContext 当中。
• ApplicationFilterChaiFactory 负责创建 Filter 对象 ApplicationFilterChain，然后遍历FilterMap s并添加符合的 Filter 包装对象 ApplicationFilterConfig。
• 执行ApplicationFilterChain的doFilter方法调用过滤器。