Struts2核心技术简介
使用Struts2框架，只要注重以下三大元素：配置文件、映射文件和Action：
全局属性文件struts.properties：保存系统运行的一些参数变量，整个系统只有一个属性文件；
映射文件struts.xml：用于配置请求映射的Action和拦截器，可以有多个映射文件；
业务控制器Action：可以使用POJO（类似JavaBean）类，也可以集成ActionSupport，在该类中不仅可以取得表单数据，还可以取得上下文变量。以下是详细说明：
1、全局属性文件struts.properties
struts.properties文件主要定义系统的属性，请看以下示例代码：
### Struts default properties ###(can be overridden by a struts.properties file in the root of the classpath) ### ###指定Struts2的配置类，默认为下面的配置，也可以通过继承 ### Specifies the Configuration used to configure Struts ### one could extend org.apache.struts2.config.Configuration ### to build one's customize way of getting the configurations parameters into Struts # struts.configuration=org.apache.struts2.config.DefaultConfiguration ###设置默认的国际化地区信息和国际化信息内码 ### This can be used to set your default locale and encoding scheme # struts.locale=en_US struts.i18n.encoding=UTF-8 ###指定对象工厂类，也可以实现自己的工厂类 ### if specified, the default object factory can be overridden here ### Note: short-hand notation is supported in some cases, such as "spring" ### Alternatively, you can provide a com.opensymphony.xwork2.ObjectFactory subclass name here # struts.objectFactory = spring ###当使用Spring的工厂类时，指定自动植入autoWrite的机制 ### specifies the autoWiring logic when using the SpringObjectFactory. ### valid values are: name, type, auto, and constructor (name is the default) struts.objectFactory.spring.autoWire = name ###使用Spring集成时，是否使用类缓存，可选值有：true和false ### indicates to the struts-spring integration if Class instances should be cached ### this should, until a future Spring release makes it possible, be left as true ### unless you know exactly what you are doing! ### valid values are: true, false (true is the default) struts.objectFactory.spring.useClassCache = true ###指定对象类型检查器，可用值有“tiger”和“notiger”，也可以使用自己的类 ### if specified, the default object type determiner can be overridden here ### Note: short-hand notation is supported in some cases, such as "tiger" or "notiger" ### Alternatively, you can provide a com.opensymphony.xwork2.util.ObjectTypeDeterminer implementation name here ### Note: By default, com.opensymphony.xwork2.util.DefaultObjectTypeDeterminer is used which handles type detection ### using generics. com.opensymphony.xwork2.util.GenericsObjectTypeDeterminer was deprecated since XWork 2, it's ### functions are integrated in DefaultObjectTypeDeterminer now. ### To disable tiger support use the "notiger" property value here. #struts.objectTypeDeterminer = tiger #struts.objectTypeDeterminer = notiger ###指定使用MIME-type multipart/form-data时的解析器 ### Parser to handle HTTP POST requests, encoded using the MIME-type multipart/form-data # struts.multipart.parser=cos # struts.multipart.parser=pell struts.multipart.parser=jakarta # uses javax.servlet.context.tempdir by default struts.multipart.saveDir= struts.multipart.maxSize=2097152 ###指定自定义的属性文件 ### Load custom property files (does not override struts.properties!) # struts.custom.properties=application,org/apache/struts2/extension/custom ###URL与Action映射处理器 ### How request URLs are mapped to and from actions #struts.mapper.class=org.apache.struts2.dispatcher.mapper.DefaultActionMapper ###指定URL的扩展名，可以指定多个扩展名，用逗号分隔，例如action、jnlp、do ### Used by the DefaultActionMapper ### You may provide a comma separated list, e.g. struts.action.extension=action,jnlp,do struts.action.extension=do ###被FilterDispatcher所使用，true表示Struts serves static content来自于内部jar ### Used by FilterDispatcher ### If true then Struts serves static content from inside its jar. ### If false then the static content must be available at <context_path>/struts struts.serve.static=true ###是否Struts过滤器中提供的静态内容应该被浏览器缓存到头部属性中 ### Used by FilterDispatcher ### This is good for development where one wants changes to the static content be ### fetch on each request. ### NOTE: This will only have effect if struts.serve.static=true ### If true -> Struts will write out header for static contents such that they will ### be cached by web browsers (using Date, Cache-Content, Pragma, Expires) ### headers). ### If false -> Struts will write out header for static contents such that they are ### NOT to be cached by web browser (using Cache-Content, Pragma, Expires ### headers) struts.serve.static.browserCache=true ###是否允许动态方法调用，如果为true，则可以配置如下的<action>参数映射 ### mappings, such as <action name="*/*" method="{2}" class="actions.{1}"> ### Set this to false if you wish to disable implicit dynamic method invocation ### via the URL request. This includes URLs like foo!bar.action, as well as params ### like method:bar (but not action:foo). ### An alternative to implicit dynamic method invocation is to use wildcard ### mappings, such as <action name="*/*" method="{2}" class="actions.{1}"> struts.enable.DynamicMethodInvocation = true ###是否在action名称中允许“/” ### Set this to true if you wish to allow slashes in your action names. If false, ### Actions names cannot have slashes, and will be accessible via any directory ### prefix. This is the traditional behavior expected of WebWork applications. ### Setting to true is useful when you want to use wildcards and store values ### in the URL, to be extracted by wildcard patterns, such as ### <action name="*/*" method="{2}" class="actions.{1}"> to match "/foo/edit" or ### "/foo/save". struts.enable.SlashesInActionNames = false ###是否可以用替代的语法%{}代替tags ### use alternative syntax that requires %{} in most places ### to evaluate expressions for String attributes for tags struts.tag.altSyntax=true ###是否为Struts开发模式 ### when set to true, Struts will act much more friendly for developers. This ### includes: ### - struts.i18n.reload = true ### - struts.configuration.xml.reload = true ### - raising various debug or ignorable problems to errors ### For example: normally a request to foo.action?someUnknownField=true should ### be ignored (given that any value can come from the web and it ### should not be trusted). However, during development, it may be ### useful to know when these errors are happening and be told of ### them right away. struts.devMode = false ###是否国际化信息自动加载 ### when set to true, resource bundles will be reloaded on _every_ request. ### this is good during development, but should never be used in production struts.i18n.reload=false ### Standard UI theme ### Change this to reflect which path should be used for JSP control tag templates by default struts.ui.theme=xhtml struts.ui.templateDir=template #sets the default template type. Either ftl, vm, or jsp struts.ui.templateSuffix=ftl ###在struts.xml 文件更改时，是否允许重载 ### Configuration reloading ### This will cause the configuration to reload struts.xml when it is changed struts.configuration.xml.reload=false ###velocity配置文件路径，默认为velocity.properties ### Location of velocity.properties file. defaults to velocity.properties struts.velocity.configfile = velocity.properties ###Cvelocity的context列表 ### Comma separated list of VelocityContext classnames to chain to the StrutsVelocityContext struts.velocity.contexts = ###velocity工具盒的位置 ### Location of the velocity toolbox struts.velocity.toolboxlocation= ### used to build URLs, such as the UrlTag struts.url.http.port = 80 struts.url.https.port = 443 ### possible values are: none, get or all struts.url.includeParams = get ###加载附加的国际化属性文件（不包含.properties） ### Load custom default resource bundles struts.custom.i18n.resources=com.demo.struts2.resources.ApplicationResources ### workaround for some app servers that don't handle HttpServletRequest.getParameterMap() ### often used for WebLogic, Orion, and OC4J struts.dispatcher.parametersWorkaround = false ### configure the Freemarker Manager class to be used ### Allows user to plug-in customised Freemarker Manager if necessary ### MUST extends off org.apache.struts2.views.freemarker.FreemarkerManager #struts.freemarker.manager.classname=org.apache.struts2.views.freemarker.FreemarkerManager ### Enables caching of FreeMarker templates ### Has the same effect as copying the templates under WEB_APP/templates struts.freemarker.templatesCache=false ### Enables caching of models on the BeanWrapper struts.freemarker.beanwrapperCache=false ### See the StrutsBeanWrapper javadocs for more information struts.freemarker.wrapper.altMap=true ### configure the XSLTResult class to use stylesheet caching. ### Set to true for developers and false for production. struts.xslt.nocache=false ###struts自动加载的配置文件列表 ### A list of configuration files automatically loaded by Struts struts.configuration.files=struts-default.xml,struts-plugin.xml,struts.xml ### Whether to always select the namespace to be everything before the last slash or not struts.mapper.alwaysSelectFullNamespace=false
2、映射文件struts.xml
Struts2框架的核心配置文件时Struts.xml，该文件主要负责管理Struts框架的业务控制器Action。该文件包含唯一的根元素<struts>，可以在该元素中添加子标签来实现自己的配置。一般开发主要用到如下的七个配置功能：
（1）属性定义元素<constant>
可以使用<constant>标签来定义一个属性，该属性与struts.properties中属性重名，并覆盖struts.properties中该属性的值。这样做的好处是，如果使用了多个映射文件时，允许每一个文件都使用不同的属性。
（2）导入子文件元素<include>
使用<include>标签来导入一个子文件，子文件与struts.xml有同样的结构，使用相同的配置语法。通过这种方式提供了一种模块化的方式来管理struts.xml文件。
（3）包定义元素<package>
<package>定义了一组<action>和拦截器元素，可以定义多个<action>元素，name表示包的名字，extends属性表示继承自struts-default.xml中所定义的包的名字。
（4）Action映射配置元素<action>
Action mapping是框架中的基本工作单元，框架通过对请求路径进行映射来决定由哪个Action来处理请求。
（5）Result配置元素<result>
Action类处理完一个请求后会返回一个字符串，这个字符串将被用来选择一个<result>元素。通常一个action mapping会有多个<result>，代表各个可能不同的结果。
（6）配置全局映射元素<global-results>
定义在<action>元素里面的<result>我们可以称之为局部<result>，除此之外我们还可以定义全局的<result>，这些全局的<result>会悲哀多个<action>所共享。框架会首先寻找嵌套在<action>元素中的<result>，如果没有匹配的就去全局<result>中去寻找。
（7）配置拦截器<interceptors>
通过使用拦截器，我们可以在Action中的方法执行之前先执行一些我们事先定义好的方法，也可以在Action中的方法执行之后立即执行一些我们事先定义好的方法。
下面请看一个struts.xml文件代码示例：
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN" "http://struts.apache.org/dtds/struts-2.0.dtd"> <struts> <constant name="struts.enable.DynamicMethodInvocation" value="false" /> <constant name="struts.devMode" value="false" /> <include file="example.xml"/> <!-- Add packages here --> <package name="main" extends="struts-default"> <action name="test" class="com.demo.struts2.actions.TestAction"> <result name="success">success.jsp</result> <result name="input">input.jsp</result> </action> </package> </struts>
3、业务控制器Action
使用Struts2框架，不需要开发ActionForm类，主要注意一下三点：
Action可以是任意的POJO（类似JavaBean）类
一般继承ActionSupport类
可以在Action中访问上下文变量