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filter的執(zhí)行順序是怎樣的？

更新時間:2020年07月08日15時43分來源:傳智播客瀏覽次數(shù):

1.引言

我們在編寫javaweb程序的時候,時常會用filter這個組件,它能將我們一些通用邏輯抽取出來,在servlet執(zhí)行業(yè)務邏輯之前運行,

達到簡化代碼和復用的目的.比如最常用的場景全站編碼和登錄驗證功能。

servlet3.0以前我們只能通過web.xml的方式配置filter,并且多個filter的執(zhí)行順序是根據(jù)你web.xml中書寫順序來決定的.

servlet3.0以后,提供了注解的方式注入filter,只需要在filter類上加上@WebFilter()注解即可,大大的簡化了開發(fā)復雜度.

2.拋出問題

注解的方式書寫的filter的執(zhí)行順序又是如何的呢?

網(wǎng)上的很多資料都說是根據(jù)filter的類名來決定,也有說是根據(jù)filter的注解的name屬性值的字母順序來決定的.

對不對呢?

2.驗證問題

我們創(chuàng)建了三個filter 來驗證此問題

filter1號

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執(zhí)行了..");
chain.doFilter(req, resp);
}

public void init(FilterConfig config) throws ServletException {

}

}

filter2號

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執(zhí)行了..");
//這是放行
chain.doFilter(req, resp);
}

public void init(FilterConfig config) throws ServletException {

}

}

filter3號

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執(zhí)行了..");
//這是放行
chain.doFilter(req, resp);
}

public void init(FilterConfig config) throws ServletException {

}

}

配上一個servlet 來訪問試試

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");
}
}

驗證結(jié)果:

3.查看源碼

可以從上面驗證看出好像并不是根據(jù)類名或者filter的name屬性的字母排序執(zhí)行,那到底是根據(jù)什么執(zhí)行的呢?

點開源碼，我們一點點探尋它的秘密。

需要搞清楚如下問題

1.filterChain是什么時候執(zhí)行的呢?

2.filterChain中的filter來源何處?

3.standardContext什么時候開始收集的過濾器集合

我們先查詢第一段源碼解密filterChain是什么時候執(zhí)行的

//在org.apache.catalina.core.StandardWrapperValve 類中有如下一個方法

public final void invoke(Request request, Response response)
throws IOException, ServletException {
//省略掉大段無關代碼
//0.生命servlet對象
Servlet servlet = null;
/**
* 省略一大段無關代碼
*/
try {
if (!unavailable) {
//1.這里創(chuàng)建正在訪問的servlet對象
servlet = wrapper.allocate();
}
} catch (UnavailableException e) {
//省略掉大段無關代碼
}

//省略大段無關代碼

//2.創(chuàng)建過濾器鏈對象
ApplicationFilterChain filterChain =
ApplicationFilterFactory.createFilterChain(request, wrapper, servlet);
try {
if ((servlet != null) && (filterChain != null)) {
// Swallow output if needed
if (context.getSwallowOutput()) {
//省略掉大段無關代碼
} else {
if (request.isAsyncDispatching()) {
request.getAsyncContextInternal().doInternalDispatch();
} else {
//3.執(zhí)行過濾鏈對象doFilter方法
filterChain.doFilter
(request.getRequest(), response.getResponse());
}
}

}
} catch (ClientAbortException | CloseNowException e) {
//省略掉大段無關代碼
}
}

我們一會兒回過頭來看它是如何創(chuàng)建過濾器鏈對象的代碼,我們先來看他是如何執(zhí)行過濾器鏈的,

過濾器鏈對象的實現(xiàn)為:

package org.apache.catalina.core;
//我們只保留跟執(zhí)行序列有關的代碼

public final class ApplicationFilterChain implements FilterChain {
//當前正在執(zhí)行的filter索引
private int pos = 0;
//總共有多少個filter匹配上了
private int n = 0;
//關聯(lián)的要執(zhí)行的servlet對象
private Servlet servlet = null;
//匹配上的filter數(shù)組
private ApplicationFilterConfig[] filters = new ApplicationFilterConfig[0];

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

if( Globals.IS_SECURITY_ENABLED ) {
//刪除無關代碼
} else {
//0.執(zhí)行內(nèi)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) {
//這個地方主義有個pos++ 進來一次 ++一次
ApplicationFilterConfig filterConfig = filters[pos++];
try {
Filter filter = filterConfig.getFilter();

//刪除大段無關代碼

if( Globals.IS_SECURITY_ENABLED ) {
//刪除大段無關代碼
} else {
//執(zhí)行過濾器鏈中的過濾器的doFilter方法
//而我們的過濾器中滿足條件后放行放行就會跳轉(zhuǎn)回來執(zhí)行過濾器鏈的
//的doFilter 也就是又回來執(zhí)行第二個
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 {
//刪除大段無關代碼
// Use potentially wrapped request from this point
if ((request instanceof HttpServletRequest) &&
(response instanceof HttpServletResponse) &&
Globals.IS_SECURITY_ENABLED ) {
//刪除大段無關代碼
} else {
//如果沒有需要執(zhí)行的filter就會執(zhí)行 servlet的service方法也就是我們寫的業(yè)務邏輯
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);
}
}
}
}

從filterChain類的源碼可以看出底層是包含了所匹配上的filter數(shù)組也就是添加進去匹配上過濾器對象是有序的添加的時候就決定了!!!

那么它是什么時候添加的呢?

2.filterChain中的filter來源何處?

其實我們在在org.apache.catalina.core.StandardWrapperValve 類的invoke方法中

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

點開這段代碼查詢把!

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

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

// 在這里創(chuàng)建ApplicationFilterChain 對象
//但是對象里還沒有filter對象
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();
//獲取ServletContext對象注冊的所有的filter數(shù)組
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();

//這里開始遍歷 filterMaps數(shù)組根據(jù)請求路徑匹配添加
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;
}

可以看出在創(chuàng)建filterChain對象時候,從ServletContext獲取所有注冊的filter的數(shù)組取出需要的添加到這次請求創(chuàng)建的filterChain對象中

而且servletContext對象的注冊的所有的過濾器本身就是一個數(shù)組本身就是有序的,所以遍歷匹配的時候,也就是有序的!

3、ServletContext什么時候開始收集的數(shù)組,從哪來的呢?

這個要從tomcat啟動的時候來看了!

而StandardContext創(chuàng)建完成以后就要開始初始化操作了!

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

好了我們現(xiàn)在查看該方法:

protected void webConfig() {

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

Set<WebXml> defaults = new HashSet<>();
defaults.add(getDefaultWebXmlFragment(webXmlParser));
//創(chuàng)建了web.xml 配置文件對象
//也就是它就代表我們項目的配置相關的信息
WebXml webXml = createWebXml();

// Parse context level web.xml
InputSource contextWebXml = getContextWebXmlSource();
//解析web.xml 配置文件
//發(fā)現(xiàn)配置文件中的 filter servlet listener等配置
//而xml的解析是從上到下所以你在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();

//省略大段無關代碼

if (!webXml.isMetadataComplete() || typeInitializerMap.size() > 0) {
// Steps 4 & 5.
//掃描編譯的類文件尋找注解方式書寫的servlet filter listener
processClasses(webXml, orderedFragments);
}
//省略大段無關代碼
}

從上面代碼可以看出web,xml配置的filter肯定是有序的了解析的時候就會收集到webXml對象的

//采用的是linkedHashset來存儲的是有序的
private final Set<FilterMap> filterMaps = new LinkedHashSet<>();

解析xml過程我們就不看了人家才是的digester的xml解析框架來做.

我們來查看processClasses(webXml, orderedFragments); 這個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) {
//獲取項目下的類路徑
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;
}
//開始根據(jù)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) {
//看看是否是個目錄
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()));
}
//遍歷目錄
for (WebResource r : webResources) {
//遞歸處理
processAnnotationsWebResource(r, fragment, handlesTypesOnly, javaClassCache);
}
}
} else if (webResource.isFile() &&
webResource.getName().endsWith(".class")) {
try (InputStream is = webResource.getInputStream()) {
//如果是類文件的話開始處理
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;
}
//處理開始
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);
//判斷是否webFilter注解如果是就添加到 webxml配置對象中
}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
}
}
}
}

從上面可以看出原來掃描類路徑的時候,就是先遍歷文件夾遍歷文件夾下類文件反射查看是否是一個帶有WebFilter注解的類

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

所有順序就是遞歸遍歷文件夾的順序一切就看遞歸的時候如何獲取下級文件夾的代碼了看它是否進行排序了?

也就是說由如下代碼決定的

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

點開這段代碼

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;
}
//繼續(xù)
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()]);
}
//繼續(xù)
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;
}
//就到這里了我們可以看到它沒有排序就是調(diào)用了
//file類的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;
}
}

來來打開file類的list方法看看