Struts2 Note One

Struts2 Notes: To introduce what Struts2 has and how to use Struts2 . Don't pay attention to the principle and core for the time being .

Learning the use of Struts2 should be from the following three aspects

①How to jump, <result> tag, <package> tag, DMI

②VS(ValueStack) and ognl expression, Struts2 label

③Interceptor

Summary of this article: Pre-content (MVC development mode, construction of Struts2 development environment), jump, <result> tag <package> tag usage, DMI

One: MVC development mode

I. Concept: MVC is a design idea that divides process control, business operations, and data display into three levels (modules), which exist independently and perform their own duties. They are a combination and invocation of each other.

II. The composition of MVC:

M	Model	Model	A representation or simulation of the objective world (business simulation, object simulation)	Service+DAO+Entity
V	View	view	Responsible for page display and data collection	HTML（JSP）+JS
C	Controller	controller	Responsible for process control and program direction	Servlet（Action）

III. Features of MVC:

1). Low coupling: The correlation between modules is not strong, and there is no inseparable relationship with a specific implementation.

2). High maintenance: based on low coupling, it is easier to modify or replace different modules, hot swap.

3). High reusability: The same data operations can serve different business functions, improving reusability.

Second, the Struts2 framework:

1. Concept: It acts as a Controller in MVC and can replace the original Servlet (Action).

2. Problems with using Servlet as controller:

3. Use Struts as a controller:

Three: Struts2 development environment to build

https://blog.csdn.net/sugar_map/article/details/80171920

四：Struts2编码（暂不通过值栈取值、通过原生作用域取值）

1：实现Action接口 import com.opensymphony.xwork2.Action;

实现execute()方法

①：通过ServletActionContext对象获取作用域对象。

获取到request可以收集客户端传来的值、将值绑定到request作用域中，通过转发传值。

②：方法的返回值类型为 String

返回null值：响应空白页面。

<result>标签的name属性与返回值匹配：响应对应的Action或JSP页面。

若方法的返回值与<result>标签的name属性值不匹配，则报错。

细节： Action对象的创建：

a. 多次请求同一个Servlet只创建一个Servlet对象。

b. 多次请求同一个Action对象会创建多个Action对象（每次请求都会创建一个）。

五、<package>包标签：

1. 作用：

I. 按功能完成模块的划分，管理不同<action>标签。

II. 功能的复用。

六：Struts2跳转详情

分为两大类：

Action->JSP，Action->Action

①首先讨论同包package的情况

1. Action ~ JSP：

I.	dispatcher（默认）：URL不变

<!-- Action->JSP 默认方式为dispatcher(可以省略)-->

<action name="showAll" class="action.EmployeeListAction">

<result name="success" type="dispatcher">emplist.jsp</result>

</action>

	II.	redirect：URL改变
<!--Action->JSP    type="redirect"(不可省略)-->
<action name="login" class="action.ControlLoginAction">
	<result name="success" type="chain">showAll</result>
	<result name="none" type="redirect">login.jsp</result>
</action>

2. Action ~ Action：

I.	chain：URL不变

<!--Action->JSP    type="chain"(不可省略)-->

<action name="login" class="action.ControlLoginAction">

<result name="success" type="chain">showAll</result>

<result name="none" type="redirect">login.jsp</result>

</action>

<!--Action->JSP    type="redirectAction"(不可省略)-->

II.	redirectAction：URL改变

<action name="showAll" class="action.EmployeeListAction">

<result name="success" type="dispatcher">emplist.jsp</result>

</action>

<action name="delete" class="action.ControlDeleteAction">

<result name="success" type="redirectAction">showAll</result>

</action>

②：不同包的情况

Action->JSP跟同包情况一致。

Action到Action的重定向（不讨论转发，因为Action为多例，不方便共享作用域。）

七：DMI(动态方法的调用)

1. 将对同一张表操作的多个请求操作，书写在一个Action中，从而减少系统Action的数量，便于后续的项目管理与维护。

3. 逻辑代码：

建议：继承ActionSupport，由父类提供默认实现。 //因实现Action接口必须覆盖execute()方法（稍显多余）

4. struts.xml配置文件：

根据method属性区分Action请求的到底是哪个方法。

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