JavaWeb中过滤器Filter的用法详解

public interface Filter {
    
    // 由web容器调用在filter实例化后调用一次，可以用来配置filter的初始信息等
    public void init(FilterConfig filterConfig) throws ServletException;

   
    // 执行该过滤器逻辑，由ApplicationFilterChain过滤器链统一调用 
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException;

    // 有web容器调用进行销毁 
    public void destroy();
}

@Slf4j(topic = "e")
@WebFilter(filterName = "loginFilter", servletNames = "dispatcher", urlPatterns = "*")
public class LoginFilter implements Filter {

  @Override
  public void init(FilterConfig filterConfig) throws ServletException {
    log.info("LoginFilter init");
  }

  @Override
  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    log.info("LoginFilter doFilter");
    httpservletRequest req = (HttpServletRequest) request;
    HttpServletResponse res = (HttpServletResponse) response;
    // 判断用户是否登录
    HttpSession session = req.getSession();
    String uri = req.getRequestURI();
    log.info("requestUri:" + uri);
    // 已经登录 | 首页 | 登录接口不拦截，其他情况重定向回首页
    if (LoginUtil.isLogin(session.getAttribute("username"))) {
      log.info("用户已登录");
      chain.doFilter(req, res);
    } else if (uri.equals(req.getContextPath() + "/") || uri.contains("login")) {
      log.info("请求首页/登录接口");
      chain.doFilter(req, res);
    } else {
      log.info("未登录请求转发到登录页");
      RequestDispatcher requestDispatcher = req.getRequestDispatcher("/");
      requestDispatcher.forward(req, res);
    }
  }

  @Override
  public void destroy() {

  }
}

 <filter>
    <filter-name>LoginFilter</filter-name>
    <filter-class>com.monian.study.filter.LoginFilter</filter-class>
  </filter>

  <filter-mapping>
    <filter-name>LoginFilter</filter-name>
    <servlet-name>dispatcher</servlet-name>
    <url-pattern>*</url-pattern>
  </filter-mapping>

 public class FilterDef implements Serializable {

    private static final long serialVersionUID = 1L;

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

    // ------------------------------------------------------------- Properties


    
    private String description = null;

    public String getDescription() {
        return this.description;
    }

    public void setDescription(String description) {
        this.description = description;
    }


    
    private String displayName = null;

    public String getDisplayName() {
        return this.displayName;
    }

    public void setDisplayName(String displayName) {
        this.displayName = displayName;
    }


    
    private transient Filter filter = null;

    public Filter getFilter() {
        return filter;
    }

    public void setFilter(Filter filter) {
        this.filter = filter;
    }


    
    private String filterClass = null;

    public String getFilterClass() {
        return this.filterClass;
    }

    public void setFilterClass(String filterClass) {
        this.filterClass = filterClass;
    }


    
    private String filterName = null;

    public String getFilterName() {
        return this.filterName;
    }

    public void setFilterName(String filterName) {
        if (filterName == null || filterName.equals("")) {
            throw new IllegalArgumentException(
                    sm.getString("filterDef.invalidFilterName", filterName));
        }
        this.filterName = filterName;
    }


    
    private String largeIcon = null;

    public String getLargeIcon() {
        return this.largeIcon;
    }

    public void setLargeIcon(String largeIcon) {
        this.largeIcon = largeIcon;
    }


    
    private final Map<String, String> parameters = new HashMap<>();

    public Map<String, String> getParameterMap() {
        return this.parameters;
    }


    
    private String smallIcon = null;

    public String getSmallIcon() {
        return this.smallIcon;
    }

    public void setSmallIcon(String smallIcon) {
        this.smallIcon = smallIcon;
    }

    private String asyncSupported = null;

    public String getAsyncSupported() {
        return asyncSupported;
    }

    public void setAsyncSupported(String asyncSupported) {
        this.asyncSupported = asyncSupported;
    }


    // --------------------------------------------------------- Public Methods


    
    public void addInitParameter(String name, String value) {

        if (parameters.containsKey(name)) {
            // The spec does not define this but the TCK expects the first
            // definition to take precedence
            return;
        }
        parameters.put(name, value);

    }


    
    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder("FilterDef[");
        sb.append("filterName=");
        sb.append(this.filterName);
        sb.append(", filterClass=");
        sb.append(this.filterClass);
        sb.append("]");
        return sb.toString();
    }


}

 public class FilterMap extends XmlEncodingBase implements Serializable {


    // ------------------------------------------------------------- Properties


    private static final long serialVersionUID = 1L;

    

    public static final int ERROR = 1;
    public static final int FORWARD = 2;
    public static final int INCLUDE = 4;
    public static final int REQUEST = 8;
    public static final int ASYNC = 16;

    // represents nothing having been set. This will be seen
    // as equal to a REQUEST
    private static final int NOT_SET = 0;

    private int dispatcherMapping = NOT_SET;

    private String filterName = null;

    public String getFilterName() {
        return this.filterName;
    }

    public void setFilterName(String filterName) {
        this.filterName = filterName;
    }


    // 过滤器作用的servlet的名称
    private String[] servletNames = new String[0];

    public String[] getServletNames() {
        if (matchAllServletNames) {
            return new String[] {};
        } else {
            return this.servletNames;
        }
    }

    public void addServletName(String servletName) {
        if ("*".equals(servletName)) {
            this.matchAllServletNames = true;
        } else {
            String[] results = new String[servletNames.length + 1];
            System.arraycopy(servletNames, 0, results, 0, servletNames.length);
            results[servletNames.length] = servletName;
            servletNames = results;
        }
    }


    
    private boolean matchAllUrlPatterns = false;

    public boolean getMatchAllUrlPatterns() {
        return matchAllUrlPatterns;
    }


    
    private boolean matchAllServletNames = false;

    public boolean getMatchAllServletNames() {
        return matchAllServletNames;
    }


    
    private String[] urlPatterns = new String[0];

    public String[] getURLPatterns() {
        if (matchAllUrlPatterns) {
            return new String[] {};
        } else {
            return this.urlPatterns;
        }
    }

    public void addURLPattern(String urlPattern) {
        addURLPatternDecoded(UDecoder.URLDecode(urlPattern, getCharset()));
    }
    public void addURLPatternDecoded(String urlPattern) {
        if ("*".equals(urlPattern)) {
            this.matchAllUrlPatterns = true;
        } else {
            String[] results = new String[urlPatterns.length + 1];
            System.arraycopy(urlPatterns, 0, results, 0, urlPatterns.length);
            results[urlPatterns.length] = UDecoder.URLDecode(urlPattern);
            urlPatterns = results;
        }
    }

    
    public void setDispatcher(String dispatcherString) {
        String dispatcher = dispatcherString.toUpperCase(Locale.ENGLISH);

        if (dispatcher.equals(DispatcherType.FORWARD.name())) {
            // apply FORWARD to the global dispatcherMapping.
            dispatcherMapping |= FORWARD;
        } else if (dispatcher.equals(DispatcherType.INCLUDE.name())) {
            // apply INCLUDE to the global dispatcherMapping.
            dispatcherMapping |= INCLUDE;
        } else if (dispatcher.equals(DispatcherType.REQUEST.name())) {
            // apply REQUEST to the global dispatcherMapping.
            dispatcherMapping |= REQUEST;
        }  else if (dispatcher.equals(DispatcherType.ERROR.name())) {
            // apply ERROR to the global dispatcherMapping.
            dispatcherMapping |= ERROR;
        }  else if (dispatcher.equals(DispatcherType.ASYNC.name())) {
            // apply ERROR to the global dispatcherMapping.
            dispatcherMapping |= ASYNC;
        }
    }

    public int getDispatcherMapping() {
        // per the SRV.6.2.5 absence of any dispatcher elements is
        // equivalent to a REQUEST value
        if (dispatcherMapping == NOT_SET) return REQUEST;

        return dispatcherMapping;
    }

    public String[] getDispatcherNames() {
        ArrayList<String> result = new ArrayList<>();
        if ((dispatcherMapping & FORWARD) != 0) {
            result.add(DispatcherType.FORWARD.name());
        }
        if ((dispatcherMapping & INCLUDE) != 0) {
            result.add(DispatcherType.INCLUDE.name());
        }
        if ((dispatcherMapping & REQUEST) != 0) {
            result.add(DispatcherType.REQUEST.name());
        }
        if ((dispatcherMapping & ERROR) != 0) {
            result.add(DispatcherType.ERROR.name());
        }
        if ((dispatcherMapping & ASYNC) != 0) {
            result.add(DispatcherType.ASYNC.name());
        }
        return result.toArray(new String[result.size()]);
    }

    // --------------------------------------------------------- Public Methods


    
    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder("FilterMap[");
        sb.append("filterName=");
        sb.append(this.filterName);
        for (int i = 0; i < servletNames.length; i++) {
            sb.append(", servletName=");
            sb.append(servletNames[i]);
        }
        for (int i = 0; i < urlPatterns.length; i++) {
            sb.append(", urlPattern=");
            sb.append(urlPatterns[i]);
        }
        sb.append("]");
        return sb.toString();
    }


}

     
    public boolean filterStart() {

        if (getLogger().isDebugEnabled()) {
            getLogger().debug("Starting filters");
        }
        // Instantiate and record a FilterConfig for each defined filter
        boolean ok = true;
        synchronized (filterConfigs) {
            filterConfigs.clear();
            // 遍历过滤器定义
            for (Entry<String,FilterDef> entry : filterDefs.entrySet()) {
                String name = entry.geTKEy();
                if (getLogger().isDebugEnabled()) {
                    getLogger().debug(" Starting filter '" + name + "'");
                }
                try {
                    // 实例化应用过滤器配置
                    ApplicationFilterConfig filterConfig =
                            new ApplicationFilterConfig(this, entry.getValue());
                    filterConfigs.put(name, filterConfig);
                } catch (Throwable t) {
                    t = ExceptionUtils.unwrapinvocationTargetException(t);
                    ExceptionUtils.handleThrowable(t);
                    getLogger().error(sm.getString(
                            "standardContext.filterStart", name), t);
                    ok = false;
                }
            }
        }

        return ok;
    }

public final class ApplicationFilterConfig implements FilterConfig, Serializable {

    private static final long serialVersionUID = 1L;

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

    private transient Log log = LogFactory.getLog(ApplicationFilterConfig.class); // must not be static

    
    private static final List<String> emptyString = Collections.emptyList();

    // ----------------------------------------------------------- Constructors


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

        super();

        this.context = context;
        this.filterDef = filterDef;
        // 过滤器初始化
        if (filterDef.getFilter() == null) {
            getFilter();
        } else {
            this.filter = filterDef.getFilter();
            getInstanceManager().newInstance(filter);
            initFilter();
        }
    }


    // ----------------------------------------------------- Instance Variables


    
    private final transient Context context;


    
    private transient Filter filter = null;


    
    private final FilterDef filterDef;

    
    private transient InstanceManager instanceManager;

    
    private ObjectName oname;

    // --------------------------------------------------- FilterConfig Methods


    
    @Override
    public String getFilterName() {
        return filterDef.getFilterName();
    }

    
    public String getFilterClass() {
        return filterDef.getFilterClass();
    }

    
    @Override
    public String getInitParameter(String name) {

        Map<String,String> map = filterDef.getParameterMap();
        if (map == null) {
            return null;
        }

        return map.get(name);

    }


    
    @Override
    public Enumeration<String> getInitParameterNames() {
        Map<String,String> map = filterDef.getParameterMap();

        if (map == null) {
            return Collections.enumeration(emptyString);
        }

        return Collections.enumeration(map.keySet());
    }


    
    @Override
    public ServletContext getServletContext() {
        return this.context.getServletContext();
    }


    
    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder("ApplicationFilterConfig[");
        sb.append("name=");
        sb.append(filterDef.getFilterName());
        sb.append(", filterClass=");
        sb.append(filterDef.getFilterClass());
        sb.append("]");
        return sb.toString();
    }

    // --------------------------------------------------------- Public Methods

    public Map<String, String> getFilterInitParameterMap() {
        return Collections.unmodifiableMap(filterDef.getParameterMap());
    }

    // -------------------------------------------------------- Package Methods

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

        // Return the existing filter instance, if any
        if (this.filter != null)
            return this.filter;

        // 根据过滤器的全限定名通过反射实例化
        String filterClass = filterDef.getFilterClass();
        this.filter = (Filter) getInstanceManager().newInstance(filterClass);

        // 初始化过滤器
        initFilter();

        return this.filter;

    }

    // 调用过滤器的init()方法，我们自定义的过滤器该init方法也由我们自定义
    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);
        }

        // Expose filter via JMX
        reGISterJMX();
    }

    
    FilterDef getFilterDef() {
        return this.filterDef;
    }
    
    private InstanceManager getInstanceManager() {
        if (instanceManager == null) {
            if (context instanceof StandardContext) {
                instanceManager = ((StandardContext)context).getInstanceManager();
            } else {
                instanceManager = new DefaultInstanceManager(null,
                        new HashMap<String, Map<String, String>>(),
                        context,
                        getClass().getClassLoader());
            }
        }
        return instanceManager;
    }
}

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

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

        // 创建并初始化一个拦截器对象
        ApplicationFilterChain filterChain = null;
        if (request instanceof Request) {
            Request req = (Request) request;
            if (Globals.IS_SECURITY_ENABLED) {
                // Security: Do not recycle
                filterChain = new ApplicationFilterChain();
            } else {
                // 从请求中取，复用过滤器链
                filterChain = (ApplicationFilterChain) req.getFilterChain();
                if (filterChain == null) {
                    filterChain = new ApplicationFilterChain();
                    req.setFilterChain(filterChain);
                }
            }
        } else {
            // Request dispatcher in use
            filterChain = new ApplicationFilterChain();
        }

        // 设置servlet
        filterChain.setServlet(servlet);
        // 是否支持异步
        filterChain.setServletSupportsAsync(wrapper.isAsyncSupported());

        // Acquire the filter mappings for this Context
        // 从上下文中获取过滤器映射信息
        StandardContext context = (StandardContext) wrapper.getParent();
        FilterMap filterMaps[] = context.findFilterMaps();

        // If there are no filter mappings, we are done
        // 未设置过滤器直接返回
        if ((filterMaps == null) || (filterMaps.length == 0))
            return filterChain;

        // Acquire the infORMation we will need to match filter mappings
        // 从request获取dispatcher以匹配 （REQUEST）
        DispatcherType dispatcher =
                (DispatcherType) request.getAttribute(Globals.DISPATCHER_TYPE_ATTR);

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

        // 获取servlet名称
        String servletName = wrapper.getName();

        // Add the relevant path-mapped filters to this filter chain
        // 过滤器链中添加路径匹配的过滤器
        for (int i = 0; i < filterMaps.length; i++) {
            // 先匹配dispatcher类型，默认是REQUEST
            if (!matchDispatcher(filterMaps[i] ,dispatcher)) {
                continue;
            }
            // 再匹配请求路径 
            if (!matchFiltersURL(filterMaps[i], requestPath))
                continue;
            ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)
                context.findFilterConfig(filterMaps[i].getFilterName());
            if (filterConfig == null) {
                // FIXME - log configuration problem
                continue;
            }
            // 添加到过滤器链中
            filterChain.addFilter(filterConfig);
        }

        // Add filters that match on servlet name second
        // 在根据servlet名称匹配过滤器添加到过滤器链中
        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
        // 返回完整的过滤器链对象
        return filterChain;
    }

 public final class ApplicationFilterChain implements FilterChain {

    // Used to enforce requirements of SRV.8.2 / SRV.14.2.5.1
    private static final ThreadLocal<ServletRequest> lastServicedRequest;
    private static final ThreadLocal<ServletResponse> lastServicedResponse;

    static {
        if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
            lastServicedRequest = new ThreadLocal<>();
            lastServicedResponse = new ThreadLocal<>();
        } else {
            lastServicedRequest = null;
            lastServicedResponse = null;
        }
    }

    // -------------------------------------------------------------- Constants


    public static final int INCREMENT = 10;


    // ----------------------------------------------------- Instance Variables

    
    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);


    
    private static final Class<?>[] classType = new Class[]{
        ServletRequest.class, ServletResponse.class, FilterChain.class};

    
    private static final Class<?>[] classTypeUsedInService = new Class[]{
        ServletRequest.class, ServletResponse.class};


    // ---------------------------------------------------- FilterChain Methods

    
    // 执行过滤器
    @Override
    public void doFilter(ServletRequest request, ServletResponse response)
        throws IOException, ServletException {

        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) {
                Exception e = pe.getException();
                if (e instanceof ServletException)
                    throw (ServletException) e;
                else if (e instanceof IOException)
                    throw (IOException) e;
                else if (e instanceof RuntimeException)
                    throw (RuntimeException) e;
                else
                    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
        // pos表示当前正在使用的过滤器在过滤器数组filters中的序号，每执行一次加1
        // n表示过滤器数目
        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doFilter执行过滤器的方法
                    filter.doFilter(request, response, this);
                }
            } catch (IOException | ServletException | RuntimeException e) {
                throw e;
            } catch (Throwable e) {
                e = ExceptionUtils.unwrapInvocationTargetException(e);
                ExceptionUtils.handleThrowable(e);
                throw new ServletException(sm.getString("filterChain.filter"), e);
            }
            return;
        }

        // We fell off the end of the chain -- call the servlet instance
        // 当所有过滤器执行完后，调用servlet的service()方法
        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) {
            e = ExceptionUtils.unwrapInvocationTargetException(e);
            ExceptionUtils.handleThrowable(e);
            throw new ServletException(sm.getString("filterChain.servlet"), e);
        } finally {
            if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
                lastServicedRequest.set(null);
                lastServicedResponse.set(null);
            }
        }
    }


    
    public static ServletRequest getLastServicedRequest() {
        return lastServicedRequest.get();
    }


    
    public static ServletResponse getLastServicedResponse() {
        return lastServicedResponse.get();
    }


    // -------------------------------------------------------- Package Methods

    
    // 添加过滤器配置信息到过滤器链
    void addFilter(ApplicationFilterConfig filterConfig) {

        // Prevent the same filter being added multiple times
        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;

    }


    
    void release() {
        for (int i = 0; i < n; i++) {
            filters[i] = null;
        }
        n = 0;
        pos = 0;
        servlet = null;
        servletSupportsAsync = false;
    }


    
    void reuse() {
        pos = 0;
    }


    
    void setServlet(Servlet servlet) {
        this.servlet = servlet;
    }


    void setServletSupportsAsync(boolean servletSupportsAsync) {
        this.servletSupportsAsync = servletSupportsAsync;
    }


    
    public void findNonAsyncFilters(Set<String> result) {
        for (int i = 0; i < n ; i++) {
            ApplicationFilterConfig filter = filters[i];
            if ("false".equalsIgnoreCase(filter.getFilterDef().getAsyncSupported())) {
                result.add(filter.getFilterClass());
            }
        }
    }
}