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
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