Struts2源码分析
Struts2架构流程图
Struts2部分类介绍
这部分从Struts2参考文档中翻译就可以了。
ActionMapper
ActionMapper其实是HttpServletRequest和Action调用请求的一个映射，它屏蔽了Action对于Request等java Servlet类的依赖。Struts2中它的默认实现类是DefaultActionMapper，ActionMapper很大的用处可以根据自己的需要来设计url格式，它自己也有Restful的实现，具体可以参考文档的docs\actionmapper.html。
ActionProxy&ActionInvocation
Action的一个代理，由ActionProxyFactory创建，它本身不包括Action实例，默认实现DefaultActionProxy是由ActionInvocation持有Action实例。ActionProxy作用是如何取得Action，无论是本地还是远程。而ActionInvocation的作用是如何执行Action，拦截器的功能就是在ActionInvocation中实现的。
ConfigurationProvider&Configuration
ConfigurationProvider就是Struts2中配置文件的解析器，Struts2中的配置文件主要是尤其实现类XmlConfigurationProvider及其子类StrutsXmlConfigurationProvider来解析
Struts2请求流程
1、客户端发送请求
2、请求先通过ActionContextCleanUp-->FilterDispatcher
3、FilterDispatcher通过ActionMapper来决定这个Request需要调用哪个Action
4、如果ActionMapper决定调用某个Action，FilterDispatcher把请求的处理交给ActionProxy，这儿已经转到它的Delegate--Dispatcher来执行
5、ActionProxy根据ActionMapping和ConfigurationManager找到需要调用的Action类
6、ActionProxy创建一个ActionInvocation的实例
7、ActionInvocation调用真正的Action，当然这涉及到相关拦截器的调用
8、Action执行完毕，ActionInvocation创建Result并返回，当然，如果要在返回之前做些什么，可以实现PreResultListener。添加PreResultListener可以在Interceptor中实现，不知道其它还有什么方式？
Struts2(2.3.4)部分代码阅读
web.xml配置：
自从struts 2.1.3以后，FilterDispatcher已标注为过时改用StrutsPrepareAndExecuteFilter。我们此文将剖析StrutsPrepareAndExecuteFilter，其在工程中作为一个Filter配置在web.xml中，配置如下：
<filter>
<filter-name>struts2</filter-name>
<filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
从org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter开始
public void init(FilterConfig filterConfig) throws ServletException {
//创建一个InitOperations初始化操作的对象
InitOperations init = new InitOperations();
try {
//封装filterConfig，其中有个主要方法getInitParameterNames将参数名字以String格式存储在List中
FilterHostConfig config = new FilterHostConfig(filterConfig);
// 初始化struts内部日志
init.initLogging(config);
//创建dispatcher对象，并读取配置文件
Dispatcher dispatcher = init.initDispatcher(config);
init.initStaticContentLoader(config, dispatcher);
//初始化类属性：prepare 、execute
prepare = new PrepareOperations(filterConfig.getServletContext(), dispatcher);
execute = new ExecuteOperations(filterConfig.getServletContext(), dispatcher);
this.excludedPatterns = init.buildExcludedPatternsList(dispatcher);
//回调空的postInit方法
postInit(dispatcher, filterConfig);
} finally {
init.cleanup();
}
}
首先看下FilterHostConfig ，只有短短的几行代码，getInitParameterNames是这个类的核心，将Filter初始化参数名称有枚举类型转为Iterator。此类的主要作为是对filterConfig 封装，源码如下：
public class FilterHostConfig implements HostConfig {
private FilterConfig config;
/*
* 构造函数
*/
public FilterHostConfig(FilterConfig config) {
this.config = config;
}
//根据init-param配置的param-name获取param-value的值
public String getInitParameter(String key) {
return config.getInitParameter(key);
}
//返回初始化参数名的List
public Iterator<String> getInitParameterNames() {
return MakeIterator.convert(config.getInitParameterNames());
}
public ServletContext getServletContext() {
return config.getServletContext();
}
}
InitOperations的initDispatcher方法。initDispatcher方法，创建dispatcher对象，并读取配置文件 。
public Dispatcher initDispatcher(HostConfig filterConfig) {
// 创建dispatcher对象，将参数传递dispatcher全局变量
Dispatcher dispatcher = createDispatcher(filterConfig);
// 初始化配置文件/读取配置文件
dispatcher.init();
return dispatcher;
}
InitOperations的createDispatcher方法。创建Dispatcher，会读取 filterConfig中的配置信息。
/*
* 创建Dispatcher，会读取 filterConfig
* 中的配置信息，将配置信息解析出来，封装成为一个Map，然后根绝servlet上下文和参数Map构造Dispatcher
*/
private Dispatcher createDispatcher(HostConfig filterConfig) {
Map<String, String> params = new HashMap<String, String>();
// 获得在web.xml中所有的配置文件，将参数放入params Map集合中
for (Iterator e = filterConfig.getInitParameterNames(); e.hasNext();) {
String name = (String) e.next();
String value = filterConfig.getInitParameter(name);
params.put(name, value);
}
// 创建Dispatcher 对象,将ServletContext()，将参数赋给Dispatcher的全局私有变量中
return new Dispatcher(filterConfig.getServletContext(), params);
}
顺着流程我们看Disptcher的init方法。init方法里就是初始读取一些配置文件等，先看init_DefaultProperties，主要是读取properties配置文件。
public void init() {
/*
* 如果 configurationManager为空，则创建configurationManager对象,
* 在configurationManager构函数 将 BeanSelectionProvider.DEFAULT_BEAN_NAME(常量值struts)
* 赋给全局变量protected String defaultFrameworkBeanName;
*/
if (configurationManager == null) {
configurationManager = createConfigurationManager(BeanSelectionProvider.DEFAULT_BEAN_NAME);
}
try {
//主要是读取properties配置文件
init_DefaultProperties(); // [1]
//读取struts-default.xml和Struts.xml的方法
init_TraditionalXmlConfigurations(); // [2]
init_LegacyStrutsProperties(); // [3]
/*
* init_CustomConfigurationProviders方式初始自定义的Provider，
* 配置类全名和实现ConfigurationProvider接口，用逗号隔开即可。
*/
init_CustomConfigurationProviders(); // [5]
//Filter的初始化参数
init_FilterInitParameters() ; // [6]
init_AliasStandardObjects() ; // [7]
Container container = init_PreloadConfiguration();
container.inject(this);
init_CheckConfigurationReloading(container);
init_CheckWebLogicWorkaround(container);
if (!dispatcherListeners.isEmpty()) {
for (DispatcherListener l : dispatcherListeners) {
l.dispatcherInitialized(this);
}
}
} catch (Exception ex) {
if (LOG.isErrorEnabled())
LOG.error("Dispatcher initialization failed", ex);
throw new StrutsException(ex);
}
}
init_DefaultProperties方法，初始化default.properties，具体的初始化操作在DefaultPropertiesProvider类中。
private void init_DefaultProperties() {
configurationManager.addContainerProvider(new DefaultPropertiesProvider());
}
打开DefaultPropertiesProvider类源码：
public void register(ContainerBuilder builder, LocatableProperties props)
throws ConfigurationException {
Settings defaultSettings = null;
try {
// 读取properties属性文件方法
defaultSettings = new PropertiesSettings(
"org/apache/struts2/default");
} catch (Exception e) {
throw new ConfigurationException(
"Could not find or error in org/apache/struts2/default.properties",
e);
}
loadSettings(props, defaultSettings);
}
再来看init_TraditionalXmlConfigurations方法，这个是读取struts-default.xml和Struts.xml的方法。
//init_TraditionalXmlConfigurations方法，这个是读取struts-default.xml和Struts.xml的方法
private void init_TraditionalXmlConfigurations() {
/*
* 首先读取web.xml中的config初始参数值
* 如果没有配置就使用默认的"struts-default.xml,struts-plugin.xml,struts.xml"，
* 这儿就可以看出为什么默认的配置文件必须取名为这三个名称了
* 如果不想使用默认的名称，直接在web.xml中配置config初始参数即可
*/
String configPaths = initParams.get("config");
if (configPaths == null) {
configPaths = DEFAULT_CONFIGURATION_PATHS;
}
String[] files = configPaths.split("\\s*[,]\\s*");
for (String file : files) {
if (file.endsWith(".xml")) {
//依次解析配置文件，xwork.xml单独解析,除xwork.xml外，
//全都调用createStrutsXmlConfigurationProvider()方法，
//StrutsXmlConfigurationProvider进行解析
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");
}
}
}
StrutsXmlConfigurationProvider类继承XmlConfigurationProvider，而XmlConfigurationProvider又实现 ConfigurationProvider接口。类XmlConfigurationProvider负责配置文件的读取和解析，addAction()方法负责读取<action>标签，并将数据保存在ActionConfig 中；addResultTypes()方法负责将<result-type>标签转化为ResultTypeConfig对象；loadInterceptors()方法负责将<interceptor>标签转化为InterceptorConfi对象；loadInterceptorStack()方法负责将<interceptor-ref>标签转化为 InterceptorStackConfig对象；loadInterceptorStacks()方法负责将<interceptor- stack>标签转化成InterceptorStackConfig对象。而上面的方法最终会被addPackage()方法调用，将所读取到的数据汇集到PackageConfig对象中。
protected PackageConfig addPackage(Element packageElement) throws ConfigurationException {
PackageConfig.Builder newPackage = buildPackageContext(packageElement);
if (newPackage.isNeedsRefresh()) {
return newPackage.build();
}
if (LOG.isDebugEnabled()) {
LOG.debug("Loaded " + newPackage);
}
// add result types (and default result) to this package
addResultTypes(newPackage, packageElement);
// load the interceptors and interceptor stacks for this package
loadInterceptors(newPackage, packageElement);
// load the default interceptor reference for this package
loadDefaultInterceptorRef(newPackage, packageElement);
// load the default class ref for this package
loadDefaultClassRef(newPackage, packageElement);
// load the global result list for this package
loadGlobalResults(newPackage, packageElement);
// load the global exception handler list for this package
loadGobalExceptionMappings(newPackage, packageElement);
// get actions
NodeList actionList = packageElement.getElementsByTagName("action");
for (int i = 0; i < actionList.getLength(); i++) {
Element actionElement = (Element) actionList.item(i);
addAction(actionElement, newPackage);
}
// load the default action reference for this package
loadDefaultActionRef(newPackage, packageElement);
PackageConfig cfg = newPackage.build();
configuration.addPackageConfig(cfg.getName(), cfg);
return cfg;
}
private List<Document> loadConfigurationFiles(String fileName, Element includeElement) {
List<Document> docs = new ArrayList<Document>();
List<Document> finalDocs = new ArrayList<Document>();
if (!includedFileNames.contains(fileName)) {
if (LOG.isDebugEnabled()) {
LOG.debug("Loading action configurations from: " + fileName);
}
includedFileNames.add(fileName);
Iterator<URL> urls = null;
InputStream is = null;
IOException ioException = null;
try {
urls = getConfigurationUrls(fileName);
} catch (IOException ex) {
ioException = ex;
}
if (urls == null || !urls.hasNext()) {
if (errorIfMissing) {
throw new ConfigurationException("Could not open files of the name " + fileName, ioException);
} else {
if (LOG.isInfoEnabled()) {
LOG.info("Unable to locate configuration files of the name "
+ fileName + ", skipping");
}
return docs;
}
}
URL url = null;
while (urls.hasNext()) {
try {
url = urls.next();
is = fileManager.loadFile(url);
InputSource in = new InputSource(is);
in.setSystemId(url.toString());
docs.add(DomHelper.parse(in, dtdMappings));
} catch (XWorkException e) {
if (includeElement != null) {
throw new ConfigurationException("Unable to load " + url, e, includeElement);
} else {
throw new ConfigurationException("Unable to load " + url, e);
}
} catch (Exception e) {
final String s = "Caught exception while loading file " + fileName;
throw new ConfigurationException(s, e, includeElement);
} finally {
if (is != null) {
try {
is.close();
} catch (IOException e) {
LOG.error("Unable to close input stream", e);
}
}
}
}
//sort the documents, according to the "order" attribute
Collections.sort(docs, new Comparator<Document>() {
public int compare(Document doc1, Document doc2) {
return XmlHelper.getLoadOrder(doc1).compareTo(XmlHelper.getLoadOrder(doc2));
}
});
for (Document doc : docs) {
Element rootElement = doc.getDocumentElement();
NodeList children = rootElement.getChildNodes();
int childSize = children.getLength();
for (int i = 0; i < childSize; i++) {
Node childNode = children.item(i);
if (childNode instanceof Element) {
Element child = (Element) childNode;
final String nodeName = child.getNodeName();
//解析每个action配置是，对于include文件可以使用通配符*来进行配置
//如Struts.xml中可配置成<include file="actions_*.xml"/>
if ("include".equals(nodeName)) {
//获得file属性 例如： <include file="example.xml"/>
String includeFileName = child.getAttribute("file");
if (includeFileName.indexOf('*') != -1) {
// handleWildCardIncludes(includeFileName, docs, child);
ClassPathFinder wildcardFinder = new ClassPathFinder();
wildcardFinder.setPattern(includeFileName);
Vector<String> wildcardMatches = wildcardFinder.findMatches();
for (String match : wildcardMatches) {
finalDocs.addAll(loadConfigurationFiles(match, child));
}
} else {
finalDocs.addAll(loadConfigurationFiles(includeFileName, child));
}
}
}
}
finalDocs.add(doc);
loadedFileUrls.add(url.toString());
}
if (LOG.isDebugEnabled()) {
LOG.debug("Loaded action configuration from: " + fileName);
}
}
return finalDocs;
}
init_CustomConfigurationProviders方式初始自定义的Provider，配置类全名和实现ConfigurationProvider接口，用逗号隔开即可。
//init_CustomConfigurationProviders方式初始自定义的Provider，配置类全名和实现ConfigurationProvider接口，用逗号隔开即可。
private void init_CustomConfigurationProviders() {
/*
* 首先读取web.xml中的configProviders初始参数值
* 如果有配置则去加载。
*/
String configProvs = initParams.get("configProviders");
if (configProvs != null) {
String[] classes = configProvs.split("\\s*[,]\\s*");
for (String cname : classes) {
try {
Class cls = ClassLoaderUtil.loadClass(cname, this.getClass());
ConfigurationProvider prov = (ConfigurationProvider)cls.newInstance();
configurationManager.addContainerProvider(prov);
} catch (InstantiationException e) {
throw new ConfigurationException("Unable to instantiate provider: "+cname, e);
} catch (IllegalAccessException e) {
throw new ConfigurationException("Unable to access provider: "+cname, e);
} catch (ClassNotFoundException e) {
throw new ConfigurationException("Unable to locate provider class: "+cname, e);
}
}
}
}
现在再回到FilterDispatcher，每次发送一个Request，FilterDispatcher都会调用doFilter方法。doFilter是过滤器的执行方法，它拦截提交的HttpServletRequest请求，HttpServletResponse响应，是strtus2的核心拦截器。
//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 != null && 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 == null) {
/*
* 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);
}
}
setEncodingAndLocale调用了dispatcher方法的prepare方法。
//setEncodingAndLocale调用了dispatcher方法的prepare方法
public void setEncodingAndLocale(HttpServletRequest request, HttpServletResponse response) {
dispatcher.prepare(request, response);
}
prepare方法，这个方法很简单只是设置了encoding 、locale ，做的只是一些辅助的工作。
public void prepare(HttpServletRequest request, HttpServletResponse response) {
String encoding = null;
if (defaultEncoding != null) {
encoding = defaultEncoding;
}
// check for Ajax request to use UTF-8 encoding strictly http://www.w3.org/TR/XMLHttpRequest/#the-send-method
if ("XMLHttpRequest".equals(request.getHeader("X-Requested-With"))) {
encoding = "utf-8";
}
Locale locale = null;
if (defaultLocale != null) {
locale = LocalizedTextUtil.localeFromString(defaultLocale, request.getLocale());
}
//设置encoding编号为UTF-8
if (encoding != null) {
applyEncoding(request, encoding);
}
if (locale != null) {
response.setLocale(locale);
}
if (paramsWorkaroundEnabled) {
request.getParameter("foo"); // simply read any parameter (existing or not) to "prime" the request
}
}
ActionContext是一个容器，这个容易主要存储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。其实质是一个Map，key是标示request、session、……的字符串，值是其对应的对象
public class ActionContext implements Serializable {
static ThreadLocal actionContext = new ThreadLocal();
Map<String, Object> context;
//省略其它的代码……
}
ActionContext上下文的创建
//创建ActionContext，初始化thread local
public ActionContext createActionContext(HttpServletRequest request, HttpServletResponse response) {
ActionContext ctx;
Integer counter = 1;
Integer oldCounter = (Integer) request.getAttribute(CLEANUP_RECURSION_COUNTER);
if (oldCounter != null) {
counter = oldCounter + 1;
}
//从ThreadLocal中获取此ActionContext变量
ActionContext oldContext = ActionContext.getContext();
if (oldContext != null) {
// detected existing context, so we are probably in a forward
ctx = new ActionContext(new HashMap<String, Object>(oldContext.getContextMap()));
} else {
ValueStack stack = dispatcher.getContainer().getInstance(ValueStackFactory.class).createValueStack();
stack.getContext().putAll(dispatcher.createContextMap(request, response, null, servletContext));
//stack.getContext()返回的是一个Map<String，Object>，根据此Map构造一个ActionContext
ctx = new ActionContext(stack.getContext());
}
request.setAttribute(CLEANUP_RECURSION_COUNTER, counter);
//将ActionContext保存ThreadLocal
ActionContext.setContext(ctx);
return ctx;
}
上面代码中dispatcher.createContextMap，如何封装相关参数：
public Map<String,Object> createContextMap(HttpServletRequest request, HttpServletResponse response,
ActionMapping mapping, ServletContext context) {
/*
* 对request包装requestMap
* 对params包装 params
* 对session包装 session
* 对context包装application
* 实际都是Map
*/
// request map wrapping the http request objects
Map requestMap = new RequestMap(request);
// parameters map wrapping the http parameters. ActionMapping parameters are now handled and applied separately
Map params = new HashMap(request.getParameterMap());
// session map wrapping the http session
Map session = new SessionMap(request);
// application map wrapping the ServletContext
Map application = new ApplicationMap(context);
//requestMap、params、session等Map封装成为一个上下文Map，逐个调用了map.put(Map p).
Map<String,Object> extraContext = createContextMap(requestMap, params, session, application, request, response, context);
if (mapping != null) {
extraContext.put(ServletActionContext.ACTION_MAPPING, mapping);
}
//返回一个封装对象的Map——extraContext
return extraContext;
}
简单看下RequestMap，其他的省略。RequestMap类实现了抽象Map，故其本身是一个Map，主要方法实现：
//map的get实现
public Object get(Object key) {
return request.getAttribute(key.toString());
}
//map的put实现
public Object put(Object key, Object value) {
Object oldValue = get(key);
entries = null;
request.setAttribute(key.toString(), value);
return oldValue;
}
Dispatcher类的serviceAction方法：
//map的get实现
public Object get(Object key) {
return request.getAttribute(key.toString());
}
//map的put实现
public Object put(Object key, Object value) {
Object oldValue = get(key);
entries = null;
request.setAttribute(key.toString(), value);
return oldValue;
}
执行Action，抛出ServletException异常：
public void executeAction(HttpServletRequest request, HttpServletResponse response, ActionMapping mapping) throws ServletException {
dispatcher.serviceAction(request, response, servletContext, mapping);
}
继续查看，dispatcher.serviceAction方法：
public void serviceAction(HttpServletRequest request, HttpServletResponse response, ServletContext context,
ActionMapping mapping) throws ServletException {
/*
* createContextMap()方法，该方法主要把Application、Session、Request的key value值拷贝到Map中，
* 并放在HashMap<String,Object>中，可以参见createContextMap方法：
*/
Map<String, Object> extraContext = createContextMap(request, response, mapping, context);
// If there was a previous value stack, then create a new copy and pass it in to be used by the new Action
//从request范围中通过struts.valueStack获得 stack对象
ValueStack stack = (ValueStack) request.getAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY);
boolean nullStack = stack == null;
if (nullStack) {
ActionContext ctx = ActionContext.getContext();
if (ctx != null) {
stack = ctx.getValueStack();
}
}
if (stack != null) {
extraContext.put(ActionContext.VALUE_STACK, valueStackFactory.createValueStack(stack));
}
String timerKey = "Handling request from Dispatcher";
try {
UtilTimerStack.push(timerKey);
//获得命名空间
String namespace = mapping.getNamespace();
//获得action配置的名称
String name = mapping.getName();
//获得action配置的方法，即method属性
String method = mapping.getMethod();
Configuration config = configurationManager.getConfiguration();
/*
* 从容器中获得ActionProxyFactory代理工厂
* ActionProxyFactory，它是创建ActionProxy来执行一个特定的命名空间和动作的名称是由调度使用XWork的切入点。
* 由ActionProxyFactory创建ActionProxy
*/
ActionProxy proxy = config.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!
//执行execute方法，并转向结果
if (mapping.getResult() != null) {
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) {
// WW-2874 Only log error if in devMode
if(devMode) {
String reqStr = request.getRequestURI();
if (request.getQueryString() != null) {
reqStr = reqStr + "?" + request.getQueryString();
}
LOG.error("Could not find action or result\n" + reqStr, e);
}
else {
if (LOG.isWarnEnabled()) {
LOG.warn("Could not find action or result", e);
}
}
sendError(request, response, context, HttpServletResponse.SC_NOT_FOUND, e);
} catch (Exception e) {
sendError(request, response, context, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e);
} finally {
UtilTimerStack.pop(timerKey);
}
}
在上面的源代码中，dispatcher.serviceAction方法里面，调用了createActionProxy方法：
ActionProxy proxy = config.getContainer().getInstance(ActionProxyFactory.class).createActionProxy( namespace, name, method, extraContext, true, false);
创建ActionPorxy对象，并调用调用proxy的prepare方法：
public ActionProxy createActionProxy(String namespace, String actionName, String methodName, Map<String, Object> extraContext, boolean executeResult, boolean cleanupContext) {
ActionInvocation inv = new DefaultActionInvocation(extraContext, true);
container.inject(inv);
return createActionProxy(inv, namespace, actionName, methodName, executeResult, cleanupContext);
}
public ActionProxy createActionProxy(ActionInvocation inv, String namespace, String actionName, String methodName, boolean executeResult, boolean cleanupContext) {
DefaultActionProxy proxy = new DefaultActionProxy(inv, namespace, actionName, methodName, executeResult, cleanupContext);
container.inject(proxy);
//调用proxy的prepare()方法
proxy.prepare();
return proxy;
}
protected void prepare() {
String profileKey = "create DefaultActionProxy: ";
try {
UtilTimerStack.push(profileKey);
config = configuration.getRuntimeConfiguration().getActionConfig(namespace, actionName);
if (config == null && unknownHandlerManager.hasUnknownHandlers()) {
config = unknownHandlerManager.handleUnknownAction(namespace, actionName);
}
if (config == null) {
throw new ConfigurationException(getErrorMessage());
}
resolveMethod();
if (!config.isAllowedMethod(method)) {
throw new ConfigurationException("Invalid method: " + method + " for action " + actionName);
}
//invocation调用初始化的方法
invocation.init(this);
} finally {
UtilTimerStack.pop(profileKey);
}
}
后面才是最主要的--ActionProxy，ActionInvocation。ActionProxy是Action的一个代理类，也就是说Action的调用是通过ActionProxy实现的，其实就是调用了ActionProxy.execute()方法，而该方法又调用了ActionInvocation.invoke()方法。归根到底，最后调用的是DefaultActionInvocation.invokeAction()方法。先看DefaultActionInvocation的init方法。
/*
* (non-Javadoc)
* @see com.opensymphony.xwork2.ActionInvocation#init(com.opensymphony.xwork2.ActionProxy)
*/
public void init(ActionProxy proxy) {
this.proxy = proxy;
Map<String, Object> contextMap = createContextMap();
// Setting this so that other classes, like object factories, can use the ActionProxy and other
// contextual information to operate
ActionContext actionContext = ActionContext.getContext();
if (actionContext != null) {
actionContext.setActionInvocation(this);
}
//创建Action，可Struts2里是每次请求都新建一个Action
createAction(contextMap);
if (pushAction) {
stack.push(action);
//将创建的action放置到的
contextMap.put("action", action);
}
//将contextMap进行封装
invocationContext = new ActionContext(contextMap);
invocationContext.setName(proxy.getActionName());
// get a new List so we don't get problems with the iterator if someone changes the list
List<InterceptorMapping> interceptorList = new ArrayList<InterceptorMapping>(proxy.getConfig().getInterceptors());
interceptors = interceptorList.iterator();
}
protected void createAction(Map<String, Object> contextMap) {
// load action
String timerKey = "actionCreate: " + proxy.getActionName();
try {
UtilTimerStack.push(timerKey);
/*
* 默认建立Action是StrutsObjectFactory，
* 实际中可以是使用Spring创建的Action，这个时候使用的是SpringObjectFactory
*/
action = objectFactory.buildAction(proxy.getActionName(), proxy.getNamespace(), proxy.getConfig(), contextMap);
} catch (InstantiationException e) {
throw new XWorkException("Unable to intantiate Action!", e, proxy.getConfig());
} catch (IllegalAccessException e) {
throw new XWorkException("Illegal access to constructor, is it public?", e, proxy.getConfig());
} catch (Exception e) {
String gripe = "";
if (proxy == null) {
gripe = "Whoa! No ActionProxy instance found in current ActionInvocation. This is bad ... very bad";
} else if (proxy.getConfig() == null) {
gripe = "Sheesh. Where'd that ActionProxy get to? I can't find it in the current ActionInvocation!?";
} else if (proxy.getConfig().getClassName() == null) {
gripe = "No Action defined for '" + proxy.getActionName() + "' in namespace '" + proxy.getNamespace() + "'";
} else {
gripe = "Unable to instantiate Action, " + proxy.getConfig().getClassName() + ", defined for '" + proxy.getActionName() + "' in namespace '" + proxy.getNamespace() + "'";
}
gripe += (((" -- " + e.getMessage()) != null) ? e.getMessage() : " [no message in exception]");
throw new XWorkException(gripe, e, proxy.getConfig());
} finally {
UtilTimerStack.pop(timerKey);
}
if (actionEventListener != null) {
action = actionEventListener.prepare(action, stack);
}
}
接下来看看DefaultActionInvocation 的invoke方法：
/*
* invoke()方法中的if(interceptors.hasNext())语句，
* 当然，interceptors里存储的是interceptorMapping列表（它包括一个Interceptor和一个name），
* 所有的截拦器必须实现Interceptor的intercept()方法，
* 而该方法的参数恰恰又是ActionInvocation，在intercept方法中还是调用invocation.invoke()，
* 从而实现了一个Interceptor链的调用。当所有的Interceptor执行完，
* 最后调用invokeActionOnly方法来执行Action相应的方法。
*/
public String invoke() throws Exception {
String profileKey = "invoke: ";
try {
UtilTimerStack.push(profileKey);
if (executed) {
throw new IllegalStateException("Action has already executed");
}
// 判断interceptors是否有拦截器
if (interceptors.hasNext()) {
final InterceptorMapping interceptor = (InterceptorMapping) interceptors.next();
String interceptorMsg = "interceptor: " + interceptor.getName();
UtilTimerStack.push(interceptorMsg);
try {
//执行拦截器，返回一个字符串返回代码
resultCode = interceptor.getInterceptor().intercept(DefaultActionInvocation.this);
}finally {
UtilTimerStack.pop(interceptorMsg);
}
} else {
//interceptor执行完了之后执行action
resultCode = invokeActionOnly();
}
// this is needed because the result will be executed, then control will return to the Interceptor, which will
// return above and flow through again
if (!executed) {
//在Result返回之前调用preResultListeners
if (preResultListeners != null) {
for (Object preResultListener : preResultListeners) {
PreResultListener listener = (PreResultListener) preResultListener;
String _profileKey = "preResultListener: ";
try {
UtilTimerStack.push(_profileKey);
listener.beforeResult(this, resultCode);
}
finally {
UtilTimerStack.pop(_profileKey);
}
}
}
// now execute the result, if we're supposed to
if (proxy.getExecuteResult()) {
/*
* action执行完了，还要根据ResultConfig返回到view，
* 也就是在invoke方法中调用executeResult方法
*/
executeResult();
}
executed = true;
}
//返回代理执行Action后的回的字符串
return resultCode;
}
finally {
UtilTimerStack.pop(profileKey);
}
}
调用invokeActionOnly方法来执行Action相应的方法：
public String invokeActionOnly() throws Exception {
return invokeAction(getAction(), proxy.getConfig());
}
protected String invokeAction(Object action, ActionConfig actionConfig) throws Exception {
//通过代理proxy.获得方法名称
String methodName = proxy.getMethod();
if (LOG.isDebugEnabled()) {
LOG.debug("Executing action method = " + actionConfig.getMethodName());
}
String timerKey = "invokeAction: " + proxy.getActionName();
try {
UtilTimerStack.push(timerKey);
boolean methodCalled = false;
Object methodResult = null;
Method method = null;
try {
//java反射机制得到要执行的方法
method = getAction().getClass().getMethod(methodName, EMPTY_CLASS_ARRAY);
} catch (NoSuchMethodException e) {
// hmm -- OK, try doXxx instead
try {
//如果没有对应的方法，则使用do+Xxxx来再次获得方法
String altMethodName = "do" + methodName.substring(0, 1).toUpperCase() + methodName.substring(1);
method = getAction().getClass().getMethod(altMethodName, EMPTY_CLASS_ARRAY);
} catch (NoSuchMethodException e1) {
// well, give the unknown handler a shot
//当未知的action、result或者方法被执行的时候，通过框架被调用。
if (unknownHandlerManager.hasUnknownHandlers()) {
try {
methodResult = unknownHandlerManager.handleUnknownMethod(action, methodName);
methodCalled = true;
} catch (NoSuchMethodException e2) {
// throw the original one
throw e;
}
} else {
throw e;
}
}
}
//执行Method
if (!methodCalled) {
methodResult = method.invoke(action, EMPTY_OBJECT_ARRAY);
}
return saveResult(actionConfig, methodResult);
} catch (NoSuchMethodException e) {
//无法找到某一特定方法时，抛出该(NoSuchMethodException)异常
throw new IllegalArgumentException("The " + methodName + "() is not defined in action " + getAction().getClass() + "");
} catch (InvocationTargetException e) {
// We try to return the source exception.
Throwable t = e.getTargetException();
if (actionEventListener != null) {
String result = actionEventListener.handleException(t, getStack());
if (result != null) {
return result;
}
}
if (t instanceof Exception) {
throw (Exception) t;
} else {
throw e;
}
} finally {
UtilTimerStack.pop(timerKey);
}
}
action执行完了，还要根据ResultConfig返回到view，也就是在invoke方法中调用executeResult方法：
private void executeResult() throws Exception {
//根据ResultConfig创建Result
result = createResult();
String timerKey = "executeResult: " + getResultCode();
try {
UtilTimerStack.push(timerKey);
if (result != null) {
/*
* 开始执行Result,
* 可以参考Result的实现，如用了比较多的ServletDispatcherResult,
* ServletActionRedirectResult,ServletRedirectResult
*/
result.execute(this);
} else if (resultCode != null && !Action.NONE.equals(resultCode)) {
throw new ConfigurationException("No result defined for action " + getAction().getClass().getName()
+ " and result " + getResultCode(), proxy.getConfig());
} else {
if (LOG.isDebugEnabled()) {
LOG.debug("No result returned for action " + getAction().getClass().getName() + " at " + proxy.getConfig()
.getLocation());
}
}
} finally {
UtilTimerStack.pop(timerKey);
}
}
public Result createResult() throws Exception {
//如果Action中直接返回的Result类型,在invokeAction()保存在explicitResult
if (explicitResult != null) {
Result ret = explicitResult;
explicitResult = null;
return ret;
}
//根据result名称获得ResultConfig，resultCode就是result的name
ActionConfig config = proxy.getConfig();
Map<String, ResultConfig> results = config.getResults();
ResultConfig resultConfig = null;
try {
//通过返回的String来匹配resultConfig
resultConfig = results.get(resultCode);
} catch (NullPointerException e) {
// swallow
}
if (resultConfig == null) {
// If no result is found for the given resultCode, try to get a wildcard '*' match.
//如果找不到对应name的ResultConfig，则使用name为通配符*的Result
//说明可以用*通配所有的Result
resultConfig = results.get("*");
}
if (resultConfig != null) {
try {
//构造result
return objectFactory.buildResult(resultConfig, invocationContext.getContextMap());
} catch (Exception e) {
LOG.error("There was an exception while instantiating the result of type " + resultConfig.getClassName(), e);
throw new XWorkException(e, resultConfig);
}
} else if (resultCode != null && !Action.NONE.equals(resultCode) && unknownHandlerManager.hasUnknownHandlers()) {
return unknownHandlerManager.handleUnknownResult(invocationContext, proxy.getActionName(), proxy.getConfig(), resultCode);
}
return null;
}
public Result buildResult(ResultConfig resultConfig, Map<String, Object> extraContext) throws Exception {
String resultClassName = resultConfig.getClassName();
Result result = null;
if (resultClassName != null) {
/*
* buildBean中会用反射机制Class.newInstance来创建bean,
* 因为Result是有状态的，所以每次请求都新建一个
*/
result = (Result) buildBean(resultClassName, extraContext);
Map<String, String> params = resultConfig.getParams();
if (params != null) {
for (Map.Entry<String, String> paramEntry : params.entrySet()) {
try {
/*
* reflectionProvider参见OgnlReflectionProvider
* resultConfig.getParams()就是result配置文件里所配置的参数<param></param>
* setProperties方法最终调用的是Ognl类的setValue方法
* 这句其实就是把param名值设置到根对象result上
*/
reflectionProvider.setProperty(paramEntry.getKey(), paramEntry.getValue(), result, extraContext, true);
} catch (ReflectionException ex) {
if (result instanceof ReflectionExceptionHandler) {
((ReflectionExceptionHandler) result).handle(ex);
}
}
}
}
}
return result;
}
--以上就是struts2一个的请求流程基本上就结束了。工作中不涉及struts2，最近不很忙，稍微看了下struts2的文档，写了个demo，从源码的角度研究了下运行原理，如有分析不当请指出，我后续逐步完善更正，大家共同提高。
——厚积薄发(yuanxw)