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filter的执行顺序是怎样的？

更新时间:2020年07月08日15时43分来源:传智播客浏览次数:

1.引言

我们在编写javaweb程序的时候,时常会用filter这个组件,它能将我们一些通用逻辑抽取出来,在servlet执行业务逻辑之前运行,

达到简化代码和复用的目的.比如最常用的场景全站编码和登录验证功能。

servlet3.0以前我们只能通过web.xml的方式配置filter,并且多个filter的执行顺序是根据你web.xml中书写顺序来决定的.

servlet3.0以后,提供了注解的方式注入filter,只需要在filter类上加上@WebFilter()注解即可,大大的简化了开发复杂度.

2.抛出问题

注解的方式书写的filter的执行顺序又是如何的呢?

网上的很多资料都说是根据filter的类名来决定,也有说是根据filter的注解的name属性值的字母顺序来决定的.

对不对呢?

2.验证问题

我们创建了三个filter 来验证此问题

filter1号

package com.jk1123.web.filter.demo01;

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;

@WebFilter("/*")
public class OrderFilter1 implements Filter {
public void destroy() {
}

public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws ServletException, IOException {
System.out.println("orderFilter1执行了..");
chain.doFilter(req, resp);
}

public void init(FilterConfig config) throws ServletException {

}

}

filter2号

package com.jk1123.web.filter.demo02;

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;

@WebFilter("/*")
public class OrderFilter2 implements Filter {
public void destroy() {
}

public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws ServletException, IOException {
System.out.println("orderFilter2执行了..");
//这是放行
chain.doFilter(req, resp);
}

public void init(FilterConfig config) throws ServletException {

}

}

filter3号

package com.jk1123.web.filter.demo03;

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;

@WebFilter("/*")
public class OrderFilter3 implements Filter {
public void destroy() {
}

public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws ServletException, IOException {
System.out.println("orderFilter3执行了..");
//这是放行
chain.doFilter(req, resp);
}

public void init(FilterConfig config) throws ServletException {

}

}

配上一个servlet 来访问试试

package com.jk1123.web.servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/foo")
public class FooServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doGet(request, response);
}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

response.getWriter().print("foo servlet");
}
}

验证结果:

3.查看源码

可以从上面验证看出好像并不是根据类名或者filter的name属性的字母排序执行,那到底是根据什么执行的呢?

点开源码，我们一点点探寻它的秘密。

需要搞清楚如下问题

1.filterChain是什么时候执行的呢?

2.filterChain中的filter来源何处?

3.standardContext什么时候开始收集的过滤器集合

我们先查询第一段源码解密filterChain是什么时候执行的

//在org.apache.catalina.core.StandardWrapperValve 类中有如下一个方法

public final void invoke(Request request, Response response)
throws IOException, ServletException {
//省略掉大段无关代码
//0.生命servlet对象
Servlet servlet = null;
/**
* 省略一大段无关代码
*/
try {
if (!unavailable) {
//1.这里创建正在访问的servlet对象
servlet = wrapper.allocate();
}
} catch (UnavailableException e) {
//省略掉大段无关代码
}

//省略大段无关代码

//2.创建过滤器链对象
ApplicationFilterChain filterChain =
ApplicationFilterFactory.createFilterChain(request, wrapper, servlet);
try {
if ((servlet != null) && (filterChain != null)) {
// Swallow output if needed
if (context.getSwallowOutput()) {
//省略掉大段无关代码
} else {
if (request.isAsyncDispatching()) {
request.getAsyncContextInternal().doInternalDispatch();
} else {
//3.执行过滤链对象doFilter方法
filterChain.doFilter
(request.getRequest(), response.getResponse());
}
}

}
} catch (ClientAbortException | CloseNowException e) {
//省略掉大段无关代码
}
}

我们一会儿回过头来看它是如何创建过滤器链对象的代码,我们先来看他是如何执行过滤器链的,

过滤器链对象的实现为:

package org.apache.catalina.core;
//我们只保留跟执行序列有关的代码

public final class ApplicationFilterChain implements FilterChain {
//当前正在执行的filter索引
private int pos = 0;
//总共有多少个filter匹配上了
private int n = 0;
//关联的要执行的servlet对象
private Servlet servlet = null;
//匹配上的filter数组
private ApplicationFilterConfig[] filters = new ApplicationFilterConfig[0];

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

if( Globals.IS_SECURITY_ENABLED ) {
//删除无关代码
} else {
//0.执行内容的doFilter方法
internalDoFilter(request,response);
}
}

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

// Call the next filter if there is one
if (pos < n) {
//这个地方主义有个pos++ 进来一次 ++一次
ApplicationFilterConfig filterConfig = filters[pos++];
try {
Filter filter = filterConfig.getFilter();

//删除大段无关代码

if( Globals.IS_SECURITY_ENABLED ) {
//删除大段无关代码
} else {
//执行过滤器链中的过滤器的doFilter方法
//而我们的过滤器中满足条件后放行放行就会跳转回来执行过滤器链的
//的doFilter 也就是又回来执行第二个
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;
}

try {
//删除大段无关代码
// Use potentially wrapped request from this point
if ((request instanceof HttpServletRequest) &&
(response instanceof HttpServletResponse) &&
Globals.IS_SECURITY_ENABLED ) {
//删除大段无关代码
} else {
//如果没有需要执行的filter就会执行 servlet的service方法也就是我们写的业务逻辑
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);
}
}
}
}

从filterChain类的源码可以看出底层是包含了所匹配上的filter数组也就是添加进去匹配上过滤器对象是有序的添加的时候就决定了!!!

那么它是什么时候添加的呢?

2.filterChain中的filter来源何处?

其实我们在在org.apache.catalina.core.StandardWrapperValve 类的invoke方法中

ApplicationFilterChain filterChain =
ApplicationFilterFactory.createFilterChain(request, wrapper, servlet);

点开这段代码查询把!

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

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

// 在这里创建ApplicationFilterChain 对象
//但是对象里还没有filter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 {
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());

// Acquire the filter mappings for this Context
StandardContext context = (StandardContext) wrapper.getParent();
//获取ServletContext对象注册的所有的filter数组
FilterMap filterMaps[] = context.findFilterMaps();

// If there are no filter mappings, we are done
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;
Object attribute = request.getAttribute(Globals.DISPATCHER_REQUEST_PATH_ATTR);
if (attribute != null){
requestPath = attribute.toString();
}

String servletName = wrapper.getName();

//这里开始遍历 filterMaps数组根据请求路径匹配添加
for (int i = 0; i < filterMaps.length; i++) {
if (!matchDispatcher(filterMaps[i] ,dispatcher)) {
continue;
}
if (!matchFiltersURL(filterMaps[i], requestPath))
continue;
ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)
context.findFilterConfig(filterMaps[i].getFilterName());
if (filterConfig == null) {
// FIXME - log configuration problem
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 the completed filter chain
return filterChain;
}

可以看出在创建filterChain对象时候,从ServletContext获取所有注册的filter的数组取出需要的添加到这次请求创建的filterChain对象中

而且servletContext对象的注册的所有的过滤器本身就是一个数组本身就是有序的,所以遍历匹配的时候,也就是有序的!

3、ServletContext什么时候开始收集的数组,从哪来的呢?

这个要从tomcat启动的时候来看了!

而StandardContext创建完成以后就要开始初始化操作了!

StandardContext.startInternal()方法---->fireLifecycleEvent()方法-->ContextConfig.lifecycleEvent()-->ContextConfig.lifecycleEventcon-->ContextConfig.con.figureStart()-->ContextConfig.webConfig()

好了我们现在查看该方法:

protected void webConfig() {

WebXmlParser webXmlParser = new WebXmlParser(context.getXmlNamespaceAware(),
context.getXmlValidation(), context.getXmlBlockExternal());

Set<WebXml> defaults = new HashSet<>();
defaults.add(getDefaultWebXmlFragment(webXmlParser));
//创建了web.xml 配置文件对象
//也就是它就代表我们项目的配置相关的信息
WebXml webXml = createWebXml();

// Parse context level web.xml
InputSource contextWebXml = getContextWebXmlSource();
//解析web.xml 配置文件
//发现配置文件中的 filter servlet listener等配置
//而xml的解析是从上到下所以你在web.xml 配置filter
//得到filter集合就是有序的
if (!webXmlParser.parseWebXml(contextWebXml, webXml, false)) {
ok = false;
}

ServletContext sContext = context.getServletContext();

//省略大段无关代码

if (!webXml.isMetadataComplete() || typeInitializerMap.size() > 0) {
// Steps 4 & 5.
//扫描编译的类文件寻找注解方式书写的servlet filter listener
processClasses(webXml, orderedFragments);
}
//省略大段无关代码
}

从上面代码可以看出web,xml配置的filter肯定是有序的了解析的时候就会收集到webXml对象的

//采用的是linkedHashset来存储的是有序的
private final Set<FilterMap> filterMaps = new LinkedHashSet<>();

解析xml过程我们就不看了人家才是的digester的xml解析框架来做.

我们来查看processClasses(webXml, orderedFragments); 这个方法是解析注解用的

protected void processClasses(WebXml webXml, Set<WebXml> orderedFragments) {
// Step 4. Process /WEB-INF/classes for annotations and
// @HandlesTypes matches
Map<String, JavaClassCacheEntry> javaClassCache = new HashMap<>();

if (ok) {
//获取项目下的类路径
WebResource[] webResources =
context.getResources().listResources("/WEB-INF/classes");

for (WebResource webResource : webResources) {
// Skip the META-INF directory from any JARs that have been
// expanded in to WEB-INF/classes (sometimes IDEs do this).
if ("META-INF".equals(webResource.getName())) {
continue;
}
//开始根据注解解析了
processAnnotationsWebResource(webResource, webXml,
webXml.isMetadataComplete(), javaClassCache);
}
}

// Step 5. Process JARs for annotations and
// @HandlesTypes matches - only need to process those fragments we
// are going to use (remember orderedFragments includes any
// container fragments)
if (ok) {
processAnnotations(
orderedFragments, webXml.isMetadataComplete(), javaClassCache);
}

// Cache, if used, is no longer required so clear it
javaClassCache.clear();
}

查看processAnnotationsWebResource方法

protected void processAnnotationsWebResource(WebResource webResource,
WebXml fragment, boolean handlesTypesOnly,
Map<String,JavaClassCacheEntry> javaClassCache) {
//看看是否是个目录
if (webResource.isDirectory()) {
WebResource[] webResources =
webResource.getWebResourceRoot().listResources(
webResource.getWebappPath());
if (webResources.length > 0) {
if (log.isDebugEnabled()) {
log.debug(sm.getString(
"contextConfig.processAnnotationsWebDir.debug",
webResource.getURL()));
}
//遍历目录
for (WebResource r : webResources) {
//递归处理
processAnnotationsWebResource(r, fragment, handlesTypesOnly, javaClassCache);
}
}
} else if (webResource.isFile() &&
webResource.getName().endsWith(".class")) {
try (InputStream is = webResource.getInputStream()) {
//如果是类文件的话开始处理
processAnnotationsStream(is, fragment, handlesTypesOnly, javaClassCache);
} catch (IOException e) {
log.error(sm.getString("contextConfig.inputStreamWebResource",
webResource.getWebappPath()),e);
} catch (ClassFormatException e) {
log.error(sm.getString("contextConfig.inputStreamWebResource",
webResource.getWebappPath()),e);
}
}
}

查看processAnnotationsStream方法

protected void processAnnotationsStream(InputStream is, WebXml fragment,
boolean handlesTypesOnly, Map<String,JavaClassCacheEntry> javaClassCache)
throws ClassFormatException, IOException {

ClassParser parser = new ClassParser(is);
JavaClass clazz = parser.parse();
checkHandlesTypes(clazz, javaClassCache);

if (handlesTypesOnly) {
return;
}
//处理开始
processClass(fragment, clazz);
}

protected void processClass(WebXml fragment, JavaClass clazz) {
AnnotationEntry[] annotationsEntries = clazz.getAnnotationEntries();
if (annotationsEntries != null) {
String className = clazz.getClassName();
for (AnnotationEntry ae : annotationsEntries) {
String type = ae.getAnnotationType();
if ("Ljavax/servlet/annotation/WebServlet;".equals(type)) {
processAnnotationWebServlet(className, ae, fragment);
//判断是否webFilter注解如果是就添加到 webxml配置对象中
}else if ("Ljavax/servlet/annotation/WebFilter;".equals(type)) {
processAnnotationWebFilter(className, ae, fragment);
}else if ("Ljavax/servlet/annotation/WebListener;".equals(type)) {
fragment.addListener(className);
} else {
// Unknown annotation - ignore
}
}
}
}

从上面可以看出原来扫描类路径的时候,就是先遍历文件夹遍历文件夹下类文件反射查看是否是一个带有WebFilter注解的类

如果是就添加到web.xml中set集合中,而那个set集合是有序的linkedset

所有顺序就是递归遍历文件夹的顺序一切就看递归的时候如何获取下级文件夹的代码了看它是否进行排序了?

也就是说由如下代码决定的

WebResource[] webResources =
webResource.getWebResourceRoot().listResources(
webResource.getWebappPath());

点开这段代码

protected WebResource[] listResources(String path, boolean validate) {
if (validate) {
path = validate(path);
}

String[] resources = list(path, false);
WebResource[] result = new WebResource[resources.length];
for (int i = 0; i < resources.length; i++) {
if (path.charAt(path.length() - 1) == '/') {
result[i] = getResource(path + resources[i], false, false);
} else {
result[i] = getResource(path + '/' + resources[i], false, false);
}
}
return result;
}
//继续
private String[] list(String path, boolean validate) {
if (validate) {
path = validate(path);
}

// Set because we don't want duplicates
// LinkedHashSet to retain the order. It is the order of the
// WebResourceSet that matters but it is simpler to retain the order
// over all of the JARs.
HashSet<String> result = new LinkedHashSet<>();
for (List<WebResourceSet> list : allResources) {
for (WebResourceSet webResourceSet : list) {
if (!webResourceSet.getClassLoaderOnly()) {
String[] entries = webResourceSet.list(path);
for (String entry : entries) {
result.add(entry);
}
}
}
}
return result.toArray(new String[result.size()]);
}
//继续
public String[] list(String path) {
checkPath(path);
String webAppMount = getWebAppMount();
if (path.startsWith(webAppMount)) {
File f = file(path.substring(webAppMount.length()), true);
if (f == null) {
return EMPTY_STRING_ARRAY;
}
//就到这里了我们可以看到它没有排序就是调用了
//file类的list方法
String[] result = f.list();
if (result == null) {
return EMPTY_STRING_ARRAY;
} else {
return result;
}
} else {
if (!path.endsWith("/")) {
path = path + "/";
}
if (webAppMount.startsWith(path)) {
int i = webAppMount.indexOf('/', path.length());
if (i == -1) {
return new String[] {webAppMount.substring(path.length())};
} else {
return new String[] {
webAppMount.substring(path.length(), i)};
}
}
return EMPTY_STRING_ARRAY;
}
}

来来打开file类的list方法看看