本文绝对原创,呕心沥血读了2天, 欢迎大家转载, 但是请朋友们尊重一下劳动成果,转载请注明出处
http://blog.csdn.net/izard999/article/details/40143439
在面试的时候,很多人经常会被问到:Struts2与Struts1的区别..我只想说, 最根本的区别是Struts2基于Filter,Struts1基于Servlet, 在Web容器中, Filter的优先级是高于Servlet的
那么上一篇文章中, 我给大家呈现那个官方的大图上面有个FilterDispatcher, 没错. 它就是Struts2的核心过滤器. 但是后来被遗弃
Deprecated. Since Struts 2.1.3, use StrutsPrepareAndExecuteFilter instead or StrutsPrepareFilter and StrutsExecuteFilter if needing using the ActionContextCleanUp filter in addition to this one
为什么遗弃我之前有所提到. 所以下面会研究StrutsPrepareAndExecuteFilter , 而不会再提及FilterDispatcher了.
在web.xml中我们指定Struts2的Filter为:
<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>从这里看得出来, Struts2官方起名字还是挺有意思的.. ng是什么.? ng是next generation的缩写, 下一代产品
下面正题开始, StrutsPrepareAndExecuteFilter源码剖析, 有三个属性:
protected PrepareOperations prepare; //准备的一些操作
protected ExecuteOperations execute; //执行的一些操作
protected List<Pattern> excludedPatterns; //排斥的一些匹配路径StrutsPrepareAndExecuteFilter与普通的Filter并无区别，方法除继承自Filter外，仅有一个回调方法，我们将按照Filter方法调用顺序，由init—>doFilter—>destroy顺序地分析源码。
1、init()
public void init(FilterConfig filterConfig) throws ServletException {
InitOperations init = new InitOperations();
Dispatcher dispatcher = null;
try {
<span style="white-space:pre"> </span> //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 ，并初始化，这部分下面我们重点分析，初始化时加载哪些些资源
dispatcher = init.initDispatcher(config);
// 初始化静态资源(静态资源后面会有讲解)
init.initStaticContentLoader(config, dispatcher);
//初始化类属性：prepare 、execute
prepare = new PrepareOperations(filterConfig.getServletContext(), dispatcher);
execute = new ExecuteOperations(filterConfig.getServletContext(), dispatcher);
//创建排斥路径列表
this.excludedPatterns = init.buildExcludedPatternsList(dispatcher);
//回调空的postInit方法
postInit(dispatcher, filterConfig);
} finally {
if (dispatcher != null) {
dispatcher.cleanUpAfterInit();
}
init.cleanup();
}
}/**
* Host configuration that wraps FilterConfig
*/
public class FilterHostConfig implements HostConfig {
private FilterConfig config;
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();
}
}
重点来了，创建并初始化Dispatcher
public Dispatcher initDispatcher( HostConfig filterConfig ) {
Dispatcher dispatcher = createDispatcher(filterConfig);
dispatcher.init();
return dispatcher;
}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，然后根据ServletContext和参数Map构造Dispatcher ：
private Dispatcher createDispatcher( HostConfig filterConfig ) {
Map<String, String> params = new HashMap<String, String>();
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);
}
很多人问Struts2配置文件的加载顺序是什么? 不用死记硬背, 源码里面就有.
Dispatcher初始化，加载struts2的相关配置文件，将按照顺序逐一加载：default.properties，struts-default.xml,struts-plugin.xml,struts.xml，……
</pre><pre name="code" class="java">/**
*初始化过程中依次加载如下配置文件
*/
public void init() {
if (configurationManager == null) {
configurationManager = new ConfigurationManager(BeanSelectionProvider.DEFAULT_BEAN_NAME);
}
try {
//加载org/apache/struts2/default.properties
init_DefaultProperties(); // [1]
//加载struts-default.xml,struts-plugin.xml,struts.xml
init_TraditionalXmlConfigurations(); // [2]
init_LegacyStrutsProperties(); // [3]
//用户自己实现的ConfigurationProviders类
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);
}
} private void init_DefaultProperties() {
configurationManager.addConfigurationProvider(new DefaultPropertiesProvider());
}public void register(ContainerBuilder builder, LocatableProperties props)
throws ConfigurationException {
Settings defaultSettings = null;
try {
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);
}其他的我们再次省略，大家可以浏览下各个初始化操作都加载了哪些文件
注意,很多人有问过我, Struts2的配置文件名可以不可以不叫struts.xml, 类似Struts1那种自己定义文件名.? 在此,我明确的告诉大家是不可以的.
因为 Dispatcher类中指定了个常量:
private static final String DEFAULT_CONFIGURATION_PATHS = "struts-default.xml,struts-plugin.xml,struts.xml";
意思是, 我们的配置文件只能是这几个名字, Struts2才会识别, 否则不识别, 读配置的顺序就是这个常量的顺序去解读的. 下面附上加载这个配置的源码
意思是, 我们的配置文件只能是这几个名字, Struts2才会识别, 否则不识别, 读配置的顺序就是这个常量的顺序去解读的. 下面附上加载这个配置的源码
private void init_TraditionalXmlConfigurations() {
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")) {
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");
}
}
}
2、doFilter()
doFilter是过滤器的执行方法，它拦截提交的HttpServletRequest请求，HttpServletResponse响应，作为strtus2的核心拦截器，在doFilter里面到底做了哪些工作，我们将逐行解读其源码，源码如下：
doFilter是过滤器的执行方法，它拦截提交的HttpServletRequest请求，HttpServletResponse响应，作为strtus2的核心拦截器，在doFilter里面到底做了哪些工作，我们将逐行解读其源码，源码如下：
public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
//父类向子类转：强转为http请求、响应
HttpServletRequest request = (HttpServletRequest) req;
HttpServletResponse response = (HttpServletResponse) res;
try {
//设置编码和国际化
prepare.setEncodingAndLocale(request, response);
//创建Action上下文（重点）
prepare.createActionContext(request, response);
//把当前Dispatcher实例放入ThreadLocal里面
prepare.assignDispatcherToThread();
if ( excludedPatterns != null && prepare.isUrlExcluded(request, excludedPatterns)) {
//如果当前路径是排斥的路径,那么此过滤器不拦截
chain.doFilter(request, response);
} else {
//包装这个Request(如果是multipart/form-data,包装成MultiPartRequestWrapper, 否则包装成StrutsRequestWrapper)
request = prepare.wrapRequest(request);
//寻找Action的映射
ActionMapping mapping = prepare.findActionMapping(request, response, true);
if (mapping == null) {
//如果没有映射,则需要判断是否是静态资源
boolean handled = execute.executeStaticResourceRequest(request, response);
if (!handled) {
chain.doFilter(request, response);
}
} else {
execute.executeAction(request, response, mapping);
}
}
} finally {
prepare.cleanupRequest(request);
}
} /**
* Sets the request encoding and locale on the response
*/
public void setEncodingAndLocale(HttpServletRequest request, HttpServletResponse response) {
dispatcher.prepare(request, response);
}下面我们看下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;
}
Locale locale = null;
if (defaultLocale != null) {
locale = LocalizedTextUtil.localeFromString(defaultLocale, request.getLocale());
}
if (encoding != null) {
try {
request.setCharacterEncoding(encoding);
} catch (Exception e) {
LOG.error("Error setting character encoding to '" + encoding + "' - ignoring.", e);
}
}
if (locale != null) {
response.setLocale(locale);
}
if (paramsWorkaroundEnabled) {
request.getParameter("foo"); // simply read any parameter (existing or not) to "prime" the request
}
}ActionContext创建（重点中的重点）
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：
static ThreadLocal actionContext = new ThreadLocal();
Map<String, Object> context;
/**
*创建Action上下文，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;
}
//注意此处是从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 {
//创建ValueStack(很重要的一个东东,后面会讲到)
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存如ThreadLocal
ActionContext.setContext(ctx);
return ctx;
}
答: 从上述源码中我们看到了, 每一次被Struts2的这个过滤器拦截的时候, 都会调用createActionContext方法, 无论当前是否有ActionContext实例存在, 都会new一个ActionContext, 只不过是如果是action之间转发的请求,那么new的时候会把之前的那个ActionContext放进去.. 而每个ActionContext都只与自己的ThreadLocal挂钩,所以是不用考虑线程安全的. 然而后面读源码也会读到, 每次请求都会产生一个Action的实例, 而Spring默认创建实例是单例的.
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) {
// 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);
}
return extraContext;
}我们简单看下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;
}public void executeAction(HttpServletRequest request, HttpServletResponse response, ActionMapping mapping) throws ServletException {
dispatcher.serviceAction(request, response, servletContext, mapping);
}
public void serviceAction(HttpServletRequest request, HttpServletResponse response, ServletContext context,
ActionMapping mapping) throws ServletException {
//封装执行的上下文环境，主要讲相关信息存储入map
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
ValueStack stack = (ValueStack) request.getAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY);
boolean nullStack = stack == null;
//这里再次强调下ValueStack的重要性(Struts2是获取--->有就直接put,没有就新建一个再put)
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);
//获取命名空间
String namespace = mapping.getNamespace();
//获取action配置的name属性
String name = mapping.getName();
//获取action配置的method属性
String method = mapping.getMethod();
Configuration config = configurationManager.getConfiguration();
//根据执行上下文参数，命名空间，名称等创建用户自定义Action的代理对象
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 {
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);
}
}
上文有提到struts配置文件的加载顺序, 再次拿出Dispatcher.init_TraditionalXmlConfigurations()方法源码
private void init_TraditionalXmlConfigurations() {
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")) {
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");
}
}
}XmlConfigurationProvider和StrutsXmlConfigurationProvider, 从源码中我看到
public class StrutsXmlConfigurationProvider extends XmlConfigurationProvider
是继承的关系, 所以我们先研究StrutsXmlConfigurationProvider
我看到了register方法
public void register(ContainerBuilder containerBuilder, LocatableProperties props) throws ConfigurationException {
if (servletContext != null && !containerBuilder.contains(ServletContext.class)) {
containerBuilder.factory(ServletContext.class, new Factory<ServletContext>() {
public ServletContext create(Context context) throws Exception {
return servletContext;
}
});
}
super.register(containerBuilder, props);
}这个里面调用了父类的
public void register(ContainerBuilder containerBuilder, LocatableProperties props) throws ConfigurationException {
if (LOG.isInfoEnabled()) {
LOG.info("Parsing configuration file [" + configFileName + "]");
}
Map<String, Node> loadedBeans = new HashMap<String, Node>();
for (Document doc : documents) {
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();
if ("bean".equals(nodeName)) {
//获取bean
String type = child.getAttribute("type");
String name = child.getAttribute("name");
String impl = child.getAttribute("class");
String onlyStatic = child.getAttribute("static");
String scopeStr = child.getAttribute("scope");
boolean optional = "true".equals(child.getAttribute("optional"));
Scope scope = Scope.SINGLETON;
if ("default".equals(scopeStr)) {
scope = Scope.DEFAULT;
} else if ("request".equals(scopeStr)) {
scope = Scope.REQUEST;
} else if ("session".equals(scopeStr)) {
scope = Scope.SESSION;
} else if ("singleton".equals(scopeStr)) {
scope = Scope.SINGLETON;
} else if ("thread".equals(scopeStr)) {
scope = Scope.THREAD;
}
if (StringUtils.isEmpty(name)) {
name = Container.DEFAULT_NAME;
}
try {
Class cimpl = ClassLoaderUtil.loadClass(impl, getClass());
Class ctype = cimpl;
if (StringUtils.isNotEmpty(type)) {
ctype = ClassLoaderUtil.loadClass(type, getClass());
}
if ("true".equals(onlyStatic)) {
// Force loading of class to detect no class def found exceptions
cimpl.getDeclaredClasses();
containerBuilder.injectStatics(cimpl);
} else {
if (containerBuilder.contains(ctype, name)) {
Location loc = LocationUtils.getLocation(loadedBeans.get(ctype.getName() + name));
if (throwExceptionOnDuplicateBeans) {
throw new ConfigurationException("Bean type " + ctype + " with the name " +
name + " has already been loaded by " + loc, child);
}
}
// Force loading of class to detect no class def found exceptions
cimpl.getDeclaredConstructors();
if (LOG.isDebugEnabled()) {
LOG.debug("Loaded type:" + type + " name:" + name + " impl:" + impl);
}
containerBuilder.factory(ctype, name, new LocatableFactory(name, ctype, cimpl, scope, childNode), scope);
}
loadedBeans.put(ctype.getName() + name, child);
} catch (Throwable ex) {
if (!optional) {
throw new ConfigurationException("Unable to load bean: type:" + type + " class:" + impl, ex, childNode);
} else {
if (LOG.isDebugEnabled()) {
LOG.debug("Unable to load optional class: #0", impl);
}
}
}
} else if ("constant".equals(nodeName)) {
//获取常量
String name = child.getAttribute("name");
String value = child.getAttribute("value");
props.setProperty(name, value, childNode);
} else if (nodeName.equals("unknown-handler-stack")) {
List<UnknownHandlerConfig> unknownHandlerStack = new ArrayList<UnknownHandlerConfig>();
NodeList unknownHandlers = child.getElementsByTagName("unknown-handler-ref");
int unknownHandlersSize = unknownHandlers.getLength();
for (int k = 0; k < unknownHandlersSize; k++) {
Element unknownHandler = (Element) unknownHandlers.item(k);
unknownHandlerStack.add(new UnknownHandlerConfig(unknownHandler.getAttribute("name")));
}
if (!unknownHandlerStack.isEmpty())
configuration.setUnknownHandlerStack(unknownHandlerStack);
}
}
}
}
}父类的register主要是解析bean标签和常量标签的, XmlConfigurationProvider类里面有一系列的load方法.就是解析struts.xml等配置文件的package信息,action信息.这里就不累赘的贴代码了. 大家自己下去看看就行了! 关键的我带着大家看看addAction方法
protected void addAction(Element actionElement, PackageConfig.Builder packageContext) throws ConfigurationException {
String name = actionElement.getAttribute("name");//获取name属性
String className = actionElement.getAttribute("class");//获取class属性
String methodName = actionElement.getAttribute("method");//获取method属性
Location location = DomHelper.getLocationObject(actionElement);//获取location
if (location == null) {
LOG.warn("location null for " + className);
}
//methodName should be null if it's not set
methodName = (methodName.trim().length() > 0) ? methodName.trim() : null;
// if there isnt a class name specified for an <action/> then try to
// use the default-class-ref from the <package/>
//为什么不配class默认是ActionSupport.?这里一目了然
if (StringUtils.isEmpty(className)) {
// if there is a package default-class-ref use that, otherwise use action support
/* if (StringUtils.isNotEmpty(packageContext.getDefaultClassRef())) {
className = packageContext.getDefaultClassRef();
} else {
className = ActionSupport.class.getName();
}*/
} else {
if (!verifyAction(className, name, location)) {
if (LOG.isErrorEnabled())
LOG.error("Unable to verify action [#0] with class [#1], from [#2]", name, className, location.toString());
return;
}
}
Map<String, ResultConfig> results;
try {
results = buildResults(actionElement, packageContext);
} catch (ConfigurationException e) {
throw new ConfigurationException("Error building results for action " + name + " in namespace " + packageContext.getNamespace(), e, actionElement);
}
//拦截器列表
List<InterceptorMapping> interceptorList = buildInterceptorList(actionElement, packageContext);
//异常映射列表
List<ExceptionMappingConfig> exceptionMappings = buildExceptionMappings(actionElement, packageContext);
ActionConfig actionConfig = new ActionConfig.Builder(packageContext.getName(), name, className)
.methodName(methodName)
.addResultConfigs(results)
.addInterceptors(interceptorList)
.addExceptionMappings(exceptionMappings)
.addParams(XmlHelper.getParams(actionElement))
.location(location)
.build();
packageContext.addActionConfig(name, actionConfig);
if (LOG.isDebugEnabled()) {
LOG.debug("Loaded " + (StringUtils.isNotEmpty(packageContext.getNamespace()) ? (packageContext.getNamespace() + "/") : "") + name + " in '" + packageContext.getName() + "' package:" + actionConfig);
}
}<!ELEMENT action ((param|result|interceptor-ref|exception-mapping)*,allowed-methods?)>
<!ATTLIST action
name CDATA #REQUIRED
class CDATA #IMPLIED
method CDATA #IMPLIED
converter CDATA #IMPLIED
>到此为止, Struts2核心源码解读工作已经基本OK了.大家也大致了解了Struts2的工作原理. 后面有关运用Struts2做程序的时候,还会根据实际情况解读相关的源码的.敬请期待.