版权声明:本文为博主原创文章,未经博主允许不得转载。 https://blog.csdn.net/u012605477/article/details/76129675
Struts2是一种基于MVC模式的javaWeb框架,本质上相当于Servlet。
所谓MVC,就是模型-视图-控制器。
Model(模型)表示应用程序核心(比如数据库记录列表)。
View(视图)显示数据(数据库记录)。
Controller(控制器)处理输入(写入数据库记录)
而Struts的作用实际上是作为控制器,建立模型层和视图层的数据交互(就是通常所说控制model和jsp之间的数据交互)
上面都是废话,你只要知道struts2能控制model和jsp之间的数据交互即可。
web程序想要使用struts2框架,除了要引用相关jar包外,还要在web.xml中对struts2进行配置,只有配置后,struts2才能对浏览器的请求进行一系列处理。
怎么在web应用中配置struts2?
首先在web.xml中添加struts2的使用,代码如下:
- <!-- 配置Struts2 核心 Filter -->
- <filter>
- <filter-name>action2</filter-name>
- <filter-class>org.apache.struts2.dispatcher.filter.StrutsPrepareAndExecuteFilter</filter-class>
- </filter>
-
- <filter-mapping>
- <filter-name>action2</filter-name>
- <url-pattern>/*</url-pattern>
- </filter-mapping>
上述代码使用了Filter,那我们就回顾一下Filter的作用。
回顾:Filter,中文名为过滤器,通过Filter可以对web服务器的资源进行管理,例如Jsp,Servlet, 静态图片文件等进行拦截,从而实现一些特殊的功能。
实现URL级别的权限访问控制、过滤敏感词汇、压缩响应信息等一些高级功能
从代码层面来讲,只要创建一个实现了Filter接口的实现类,然后将这个类在web.xml进行配置,那么这个类就可以让用户在访问某个目标资源之前,对访问的请求和响应进行拦截。
更多介绍可以看我的另外一篇文章:http://blog.csdn.net/u012605477/article/details/75258358
注意:Struts2在web.xml中看来就是一个Filter,只不过其实现类StrutsPrepareAndExecuteFilter不是我们写的,是Struts2的。
为了验证StrutsPrepareAndExecuteFilter也实现了Filter接口,我们将其和我们自写的过滤器进行对比:
下面是自写的过滤器FilterA配置:
- <filter>
- <filter-name>FilterA</filter-name>
- <filter-class>com.strategy.jpa.FilterA</filter-class>
- </filter>
- <filter-mapping>
- <filter-name>FilterA</filter-name>
- <url-pattern>/*</url-pattern>
- </filter-mapping>
自写FilterA的代码:- package com.strategy.jpa;
-
- import java.io.IOException;
-
- import javax.servlet.Filter;
- import javax.servlet.FilterChain;
- import javax.servlet.FilterConfig;
- import javax.servlet.ServletException;
- import javax.servlet.ServletRequest;
- import javax.servlet.ServletResponse;
-
- public class FilterA implements Filter {
-
- public void init(FilterConfig filterConfig) throws ServletException {
-
- }
-
- public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
- throws IOException, ServletException {
-
-
- chain.doFilter(request, response);
- response.reset();
-
- }
-
- public void destroy() {
-
- }
-
- }
web中配置Struts2的代码:- * $Id: DefaultActionSupport.java 651946 2008-04-27 13:41:38Z apetrelli $
- package org.apache.struts2.dispatcher.filter;
-
- import org.apache.logging.log4j.LogManager;
- import org.apache.logging.log4j.Logger;
- import org.apache.struts2.RequestUtils;
- import org.apache.struts2.StrutsStatics;
- import org.apache.struts2.dispatcher.Dispatcher;
- import org.apache.struts2.dispatcher.mapper.ActionMapping;
- import org.apache.struts2.dispatcher.ExecuteOperations;
- import org.apache.struts2.dispatcher.InitOperations;
- import org.apache.struts2.dispatcher.PrepareOperations;
-
- import javax.servlet.Filter;
- import javax.servlet.FilterChain;
- import javax.servlet.FilterConfig;
- import javax.servlet.ServletException;
- import javax.servlet.ServletRequest;
- import javax.servlet.ServletResponse;
- import javax.servlet.http.HttpServletRequest;
- import javax.servlet.http.HttpServletResponse;
- import java.io.IOException;
- import java.util.List;
- import java.util.regex.Pattern;
-
- /**
- * Handles both the preparation and execution phases of the Struts dispatching process. This filter is better to use
- * when you don't have another filter that needs access to action context information, such as Sitemesh.
- */
- public class StrutsPrepareAndExecuteFilter implements StrutsStatics, Filter {
-
- private static final Logger LOG = LogManager.getLogger(StrutsPrepareAndExecuteFilter.class);
-
- protected PrepareOperations prepare;
- protected ExecuteOperations execute;
- protected List<Pattern> excludedPatterns = ;
-
- public void init(FilterConfig filterConfig) throws ServletException {
- InitOperations init = new InitOperations();
- Dispatcher dispatcher = ;
- try {
- FilterHostConfig config = new FilterHostConfig(filterConfig);
- init.initLogging(config);
- dispatcher = init.initDispatcher(config);
- init.initStaticContentLoader(config, dispatcher);
-
- prepare = new PrepareOperations(dispatcher);
- execute = new ExecuteOperations(dispatcher);
- this.excludedPatterns = init.buildExcludedPatternsList(dispatcher);
-
- postInit(dispatcher, filterConfig);
- } finally {
- if (dispatcher != ) {
- dispatcher.cleanUpAfterInit();
- }
- init.cleanup();
- }
- }
-
- /**
- * Callback for post initialization
- *
- * @param dispatcher the dispatcher
- * @param filterConfig the filter config
- */
- protected void postInit(Dispatcher dispatcher, FilterConfig filterConfig) {
- }
-
- public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
-
- HttpServletRequest request = (HttpServletRequest) req;
- HttpServletResponse response = (HttpServletResponse) res;
-
- try {
- String uri = RequestUtils.getUri(request);
- if (excludedPatterns != && prepare.isUrlExcluded(request, excludedPatterns)) {
- LOG.trace("Request {} is excluded from handling by Struts, passing request to other filters", uri);
- chain.doFilter(request, response);
- } else {
- LOG.trace("Checking if {} is a static resource", uri);
- boolean handled = execute.executeStaticResourceRequest(request, response);
- if (!handled) {
- LOG.trace("Assuming uri {} as a normal action", uri);
- prepare.setEncodingAndLocale(request, response);
- prepare.createActionContext(request, response);
- prepare.assignDispatcherToThread();
- request = prepare.wrapRequest(request);
- ActionMapping mapping = prepare.findActionMapping(request, response, true);
- if (mapping == ) {
- LOG.trace("Cannot find mapping for {}, passing to other filters", uri);
- chain.doFilter(request, response);
- } else {
- LOG.trace("Found mapping {} for {}", mapping, uri);
- execute.executeAction(request, response, mapping);
- }
- }
- }
- } finally {
- prepare.cleanupRequest(request);
- }
- }
-
- public void destroy() {
- prepare.cleanupDispatcher();
- }
-
- }
对比可知,struts2也实现了Filter接口,只是他比我们自己写的FilterA多实现了一个接口StrutsStatics,其它的没有变化。我们对上面的代码进行了解:
在Init方法里面,我们看到有一个config对象,该类对象的作用是对FilterConfig进行封装。
- package org.apache.struts2.dispatcher.filter;
-
- import org.apache.struts2.util.MakeIterator;
-
- import javax.servlet.FilterConfig;
- import javax.servlet.ServletContext;
- import java.util.Iterator;
-
- import org.apache.struts2.dispatcher.HostConfig;
-
- /**
- * Host configuration that wraps FilterConfig
- */
- public class FilterHostConfig implements HostConfig {
-
- private FilterConfig config;
-
- public FilterHostConfig(FilterConfig config) {
- this.config = config;
- }
- public String getInitParameter(String key) {
- return config.getInitParameter(key);
- }
-
- public Iterator<String> getInitParameterNames() {
- return MakeIterator.convert(config.getInitParameterNames());
- }
-
- public ServletContext getServletContext() {
- return config.getServletContext();
- }
- }
然后又在Init方法里面通过创建的config对象,并调用initDispatcher方法创建了转发器对象dispatcher对象。以及通过initLogging方法初始化日志记录器。
- private Dispatcher createDispatcher( HostConfig filterConfig ) {
- Map<String, String> params = new HashMap<>();
- for ( Iterator e = filterConfig.getInitParameterNames(); e.hasNext(); ) {
- String name = (String) e.next();
- String value = filterConfig.getInitParameter(name);
- params.put(name, value);
- }
- return new Dispatcher(filterConfig.getServletContext(), params);
- }
-
- public void cleanup() {
- ActionContext.setContext();
- }
- public void initLogging( HostConfig filterConfig ) {
- String factoryName = filterConfig.getInitParameter("loggerFactory");
- if (factoryName != ) {
- try {
- Class cls = ClassLoaderUtil.loadClass(factoryName, this.getClass());
- LoggerFactory fac = (LoggerFactory) cls.newInstance();
- LoggerFactory.setLoggerFactory(fac);
- } catch ( InstantiationException e ) {
- System.err.println("Unable to instantiate logger factory: " + factoryName + ", using default");
- e.printStackTrace();
- } catch ( IllegalAccessException e ) {
- System.err.println("Unable to access logger factory: " + factoryName + ", using default");
- e.printStackTrace();
- } catch ( ClassNotFoundException e ) {
- System.err.println("Unable to locate logger factory class: " + factoryName + ", using default");
- e.printStackTrace();
- }
- }
- }
接下来调用了init对象initStaticContentLoader(config, dispatcher);方法加载一些静态资源。
- public StaticContentLoader initStaticContentLoader( HostConfig filterConfig, Dispatcher dispatcher ) {
- StaticContentLoader loader = dispatcher.getContainer().getInstance(StaticContentLoader.class);
- loader.setHostConfig(filterConfig);
- return loader;
- }
最重要的就是dispatcher,它主要将filter拦截到的请求转入struts2的请求处理模块,我们必须知道这一点。
其次是FilterConfig,它将我们在web.xml中的Filter的配置信息也保存到了dispatcher中。下面是该对象的构造方法。
- public Dispatcher(ServletContext servletContext, Map<String, String> initParams) {
- this.servletContext = servletContext;
- this.initParams = initParams;
- }
接下来就是prepare和execute对象,和InitOperations类似,也是进行了封装一些操作,都是截取一部分重要的代码。
- public PrepareOperations(Dispatcher dispatcher) {
- this.dispatcher = dispatcher;
- }
- public ActionContext createActionContext(HttpServletRequest request, HttpServletResponse response) {
- ActionContext ctx;
- Integer counter = 1;
- Integer oldCounter = (Integer) request.getAttribute(CLEANUP_RECURSION_COUNTER);
- if (oldCounter != ) {
- counter = oldCounter + 1;
- }
-
- ActionContext oldContext = ActionContext.getContext();
- if (oldContext != ) {
- // detected existing context, so we are probably in a forward
- ctx = new ActionContext(new HashMap<>(oldContext.getContextMap()));
- } else {
- ValueStack stack = dispatcher.getContainer().getInstance(ValueStackFactory.class).createValueStack();
- stack.getContext().putAll(dispatcher.createContextMap(request, response, ));
- ctx = new ActionContext(stack.getContext());
- }
- request.setAttribute(CLEANUP_RECURSION_COUNTER, counter);
- ActionContext.setContext(ctx);
- return ctx;
- }
execute对象- public ExecuteOperations(Dispatcher dispatcher) {
- this.dispatcher = dispatcher;
- }
-
- public boolean executeStaticResourceRequest(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
- // there is no action in this request, should we look for a static resource?
- String resourcePath = RequestUtils.getServletPath(request);
-
- if ("".equals(resourcePath) && != request.getPathInfo()) {
- resourcePath = request.getPathInfo();
- }
-
- StaticContentLoader staticResourceLoader = dispatcher.getContainer().getInstance(StaticContentLoader.class);
- if (staticResourceLoader.canHandle(resourcePath)) {
- staticResourceLoader.findStaticResource(resourcePath, request, response);
- // The framework did its job here
- return true;
-
- } else {
- // this is a normal request, let it pass through
- return false;
- }
- }
从上面的代码可以看出,这两个对象封装了请求预处理和请求处理的操作,当处理请求时方法被调用
在上述的代码中有个很重要的方法未罗列出来,那就是Disptcher中得init方法,该方法初始读取一些配置文件,包含我们想要知道的读取struts2.xml的方法。
- public void init() {
-
- if (configurationManager == ) {
- configurationManager = createConfigurationManager(DefaultBeanSelectionProvider.DEFAULT_BEAN_NAME);
- }
-
- try {
- init_FileManager();
- init_DefaultProperties(); // [1]
- init_TraditionalXmlConfigurations(); // [2]
- init_LegacyStrutsProperties(); // [3]
- init_CustomConfigurationProviders(); // [5]
- init_FilterInitParameters() ; // [6]
- init_AliasStandardObjects() ; // [7]
-
- Container container = init_PreloadConfiguration();
- container.inject(this);
- init_CheckWebLogicWorkaround(container);
-
- if (!dispatcherListeners.isEmpty()) {
- for (DispatcherListener l : dispatcherListeners) {
- l.dispatcherInitialized(this);
- }
- }
- errorHandler.init(servletContext);
-
- } catch (Exception ex) {
- LOG.error("Dispatcher initialization failed", ex);
- throw new StrutsException(ex);
- }
- }
上面是init方法,里面调用了诸多读取配置文件的方法,包含我们想要知道的读取struts.xml的方法:- private void init_TraditionalXmlConfigurations() {
- String configPaths = initParams.get("config");
- if (configPaths == ) {
- configPaths = DEFAULT_CONFIGURATION_PATHS;
- }
- String[] files = configPaths.split("\\s*[,]\\s*");
- for (String file : files) {
- if (file.endsWith(".xml")) {
- if ("xwork.xml".equals(file)) {
- configurationManager.addContainerProvider(createXmlConfigurationProvider(file, false));
- } else {
- configurationManager.addContainerProvider(createStrutsXmlConfigurationProvider(file, false, servletContext));
- }
- } else {
- throw new IllegalArgumentException("Invalid configuration file name");
- }
- }
- }
在上面的代码中,设定了读取struts.xml的默认路径,其内容如下:private static final String DEFAULT_CONFIGURATION_PATHS = "struts-default.xml,struts-plugin.xml,struts.xml";
至此,web应用配置struts2框架,以及struts2如何将Filter封装成struts2的,甚至如何读取struts.xml以及其他配置,并进行相关struts2参数初始化都有了大概了解,接下来说一下Action。回到StrutsPrepareAndExecuteFilter类的doFilter中,
- //每次发送一个Request,StrutsPrepareAndExecuteFilter都会调用doFilter方法
- public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
-
- HttpServletRequest request = (HttpServletRequest) req;
- HttpServletResponse response = (HttpServletResponse) res;
-
- try {
- //设置编码和国际化
- prepare.setEncodingAndLocale(request, response);
- //ActionContext创建
- prepare.createActionContext(request, response);
- prepare.assignDispatcherToThread();
- if ( excludedPatterns != && prepare.isUrlExcluded(request, excludedPatterns)) {
- chain.doFilter(request, response);
- } else {
- request = prepare.wrapRequest(request);
- ActionMapping mapping = prepare.findActionMapping(request, response, true);
- //如果找不到对应的action配置
- if (mapping == ) {
- /*
- * 就是如果path是以“/struts”开头,则到初始参数packages配置的包路径去查找对应的静态资源并输出到页面流中,
- * 当然.class文件除外。如果再没有则跳转到404
- */
- boolean handled = execute.executeStaticResourceRequest(request, response);
- if (!handled) {
- chain.doFilter(request, response);
- }
- } else {
- /*
- * 找到对应action配置文件后,调用ExecuteOperations类中executeAction,
- * 开始谳用Action的方法。
- */
- execute.executeAction(request, response, mapping);
- }
- }
- } finally {
- prepare.cleanupRequest(request);
- }
- }
相关准备(prepare)方法,设置编码的方法不再叙述(setEncodingAndLocale),我们主要说一下ActionContext。prepare.createActionContext(request, response);
ActionContext是一个struts2容器,主要存储request、session、application、parameters等相关信息。
ActionContext是一个线程的本地变量,这意味着不同的action之间不会共享ActionContext,所以也不用考虑线程安全问题
- public ActionContext createActionContext(HttpServletRequest request, HttpServletResponse response) {
- ActionContext ctx;
- Integer counter = 1;
- Integer oldCounter = (Integer) request.getAttribute(CLEANUP_RECURSION_COUNTER);
- if (oldCounter != ) {
- counter = oldCounter + 1;
- }
-
- ActionContext oldContext = ActionContext.getContext();
- if (oldContext != ) {
- // detected existing context, so we are probably in a forward
- ctx = new ActionContext(new HashMap<>(oldContext.getContextMap()));
- } else {
- ValueStack stack = dispatcher.getContainer().getInstance(ValueStackFactory.class).createValueStack();
- stack.getContext().putAll(dispatcher.createContextMap(request, response, ));
- ctx = new ActionContext(stack.getContext());
- }
- request.setAttribute(CLEANUP_RECURSION_COUNTER, counter);
- ActionContext.setContext(ctx);
- return ctx;
- }
我们再看一下ActionContext是什么,取部分代码,由此可知ActionContext是一个键值对集合,跟Spring中的bean类似:
- public class ActionContext implements Serializable {
-
- static ThreadLocal<ActionContext> actionContext = new ThreadLocal<>();
-
- private Map<String, Object> context;
-
- public ActionContext(Map<String, Object> context) {
- this.context = context;
- }
有了创建Action的方法,肯定有使用Action的方法,我们现在去找使用的方法:- public void serviceAction(HttpServletRequest request, HttpServletResponse response, ActionMapping mapping)
- throws ServletException {
-
- Map<String, Object> extraContext = createContextMap(request, response, mapping);
-
- // If there was a previous value stack, then create a new copy and pass it in to be used by the new Action
- ValueStack stack = (ValueStack) request.getAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY);
- boolean nullStack = stack == ;
- if (nullStack) {
- ActionContext ctx = ActionContext.getContext();
- if (ctx != ) {
- stack = ctx.getValueStack();
- }
- }
- if (stack != ) {
- extraContext.put(ActionContext.VALUE_STACK, valueStackFactory.createValueStack(stack));
- }
-
- String timerKey = "Handling request from Dispatcher";
- try {
- UtilTimerStack.push(timerKey);
- String namespace = mapping.getNamespace();
- String name = mapping.getName();
- String method = mapping.getMethod();
-
- ActionProxy proxy = getContainer().getInstance(ActionProxyFactory.class).createActionProxy(
- namespace, name, method, extraContext, true, false);
-
- request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, proxy.getInvocation().getStack());
-
- // if the ActionMapping says to go straight to a result, do it!
- if (mapping.getResult() != ) {
- Result result = mapping.getResult();
- result.execute(proxy.getInvocation());
- } else {
- proxy.execute();
- }
-
- // If there was a previous value stack then set it back onto the request
- if (!nullStack) {
- request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, stack);
- }
- } catch (ConfigurationException e) {
- logConfigurationException(request, e);
- sendError(request, response, HttpServletResponse.SC_NOT_FOUND, e);
- } catch (Exception e) {
- if (handleException || devMode) {
- sendError(request, response, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e);
- } else {
- throw new ServletException(e);
- }
- } finally {
- UtilTimerStack.pop(timerKey);
- }
- }
在上面的try语句里面我们可以得知,struts是怎么通过命名空间,读取action的配置,以及action的method方法,
尤其是如何从容器中获得ActionProxyFactory代理工厂 ,是怎么创建ActionProxy来执行一个特定的命名空间和动作的。
以及怎么通过我们在struts2中设定的跳转方法,跳转到指定页面的。
- //执行execute方法,并转向结果
- if (mapping.getResult() != ) {
- Result result = mapping.getResult();
- result.execute(proxy.getInvocation());
- } else {
- proxy.execute();
- }
至此,对于Struts2是如何工作的,怎么读取xml的,如何搭建在web应用中基本叙述完了,更详细的实在说不完,各位大佬可以看下下面这位大神的博客,很给力,就是看起来太繁琐。
另外,本文部分来源于该大神,未通知,深表歉意。
http://blog.csdn.net/yuan_xw/article/details/7838123