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
