Monday, December 31, 2012

Hello Struts

Go through MVC first:

Project: MyEclipse -> MyHelloStruts

1. Session

Class ActionContext

static ActionContext getContext()
Returns the ActionContext specific to the current thread.

Map getSession()
Gets the Map of HttpSession values when in a servlet environment or a generic session map otherwise.

getContext

public static ActionContext getContext()

Returns the ActionContext specific to the current thread.

Returns:: the ActionContext for the current thread, is never null.

getSession

public Map getSession()

Gets the Map of HttpSession values when in a servlet environment or a generic session map otherwise.

Returns:: the Map of HttpSession values when in a servlet environment or a generic session map otherwise.

JavaScript

http://www.w3schools.com/js/js_ex_dom.asp

Sunday, December 30, 2012

Reflection - Class.forname(String s)

Reflection

Here is one example that uses returned Class to create an instance of AClass:

package com.xyzws;
class AClass {
  public AClass() {
    System.out.println("AClass's Constructor");
  }
  static { 
    System.out.println("static block in AClass");
  }
}

-------------------------------------------------------

public class Program { 
  public static void main(String[] args) {
    try { 
      System.out.println("The first time calls forName:");
      Class c   = Class.forName("com.xyzws.AClass"); //return the Class object (Every Class has an class object)
      AClass a = (AClass)c.newInstance(); //create a Instance using this Object

      System.out.println("The second time calls forName:");
      Class c1 = Class.forName("com.xyzws.AClass");

    } catch (ClassNotFoundException e) {
            ...
    } catch (InstantiationException e) {
            ...
    } catch (IllegalAccessException e) {
            ...
    }
        
  }
}

The output is

The first time calls forName:
static block in AClass
AClass's Constructor
The second time calls forName:  
//Calss has been loaded so there is not "static block in AClass" printing out

Why use reflection?

You can decide whether or not to create an instance at runtime.

if "com.xyzws.AClass" exist -> create

else not create anything

Struts 2 权威指南 P606 DAO factory 使用了这种方法，使得系统添加DAO组件时，无需修改代码，只需要在DD里面加入就行了。

Struts2学习笔记1

struts hello world - useful!
http://www.dzone.com/tutorials/java/struts-2/struts-2-example/struts-2-hello-world-example-1.html

Q:How to generate Bean in Eclipse automatically?
A： Source -> generate getters and setters
See:
Eclipse快速上手Hibernate--1. 入门实例
http://blog.csdn.net/javamxj/article/details/335076

Q:

为什么加filter的struts2找不到jsp页面？不加就没问题

http://www.crazyit.org/thread-7026-1-1.html
A:
Sometime different versions of struts require different library.

Struts 2 Hello World Tutorial

In this tutorial we will see how to create a simpe Struts 2 Hello World Application. The following files are needed to create a Hello World Application.

web.xml
struts.xml
HelloWorld.java
index.jsp
success.jsp

The following picture shows the directory structure of the Hello World application.

web.xml

web.xml is used to configure the servlet container properties of the hello world appliation. The filter and the filter-mapping elements are used to setup the Struts 2 FilterDispatcher. The filter is mapped to the URL pattern "/*". This means all the incoming request that targets to the Struts 2 action will be handled by FilterDispatcher class.

<filter>

<filter-name>struts2</filter-name>

<filter-class>org.apache.struts2.dispatcher.FilterDispatcher </filter-class>

</filter>

<filter-mapping>

<filter-name>struts2</filter-name>

<url-pattern>/*</url-pattern>

</filter-mapping>

<welcome-file-list>

<welcome-file>index.jsp</welcome-file>

</welcome-file-list>

The gateway for our hello world application is index.jsp file. The index.jsp file should be mentioned in web.xml as shown above.

struts.xml

The entry point to the XML declarative architecture is struts.xml file. The struts.xml file contains the following action mapping.

<struts>

<package name="default" extends="struts-default">

<action name="HelloWorld" class="vaannila.HelloWorld">

<result name="SUCCESS">/success.jsp</result>

</action>

</package>

</struts>

index.jsp

The Struts 2 UI tags are simple and powerful. To use the struts tags in the jsp page the following taglib directive should be included.

PS: You have to use Struts 2 tag otherwise the program won't work. OR you can simply add ".action" like action = "HelloWworld.action" in the form instead of using Struts taglib.

这两种方法都是为了标明这个request是需要拦截并dispatch到相应的.java中去的。filter（拦截器）就是为了-> recognize and then dispatch requests.

<%@taglib uri="/struts-tags" prefix="s" %>

 

<html>

<head>

<title>Hello World</title>

</head>

<body>

<s:form action="HelloWorld" >

<s:textfield name="userName" label="User Name" />

<s:submit />

</s:form>

</body>

</html>

form action = "HelloWorld"

HelloWorld must have a execute()

HelloWorld.java

As you see the HelloWorld class is very simple. It contains two properties one for the user name and the other for displaying the message.

public class HelloWorld {

 

private String message;

 

private String userName;

 

public HelloWorld() {

}

 

public String execute() {

setMessage("Hello " + getUserName());

return "SUCCESS";

}

 

public String getMessage() {

return message;

}

 

public void setMessage(String message) {

this.message = message;

}

 

public String getUserName() {

return userName;

}

 

public void setUserName(String userName) {

this.userName = userName;

}

 

}

In the execute() method of the HelloWorld action we compose the message to be displayed. Note we need not have a seperate form bean like struts 1 to access the form data. We can have a simple java class as action. The action need not extend any class or implement any interface. The only obligation is that you need to have an execute() method which returns a String and has a public scope.

success.jsp

In the success page we display the "Hello User" message using the property tag.

<%@taglib uri="/struts-tags" prefix="s" %>

<html>

<head>

<title>Hello World</title>

</head>

<body>

<h1><s:property value="message" /></h1>

</body>

</html>

Extract the downloaded files into the webapps folder of Tomcat. Start the Tomcat server. Type the following url in the browser "http://localhost:8080/Example1/index.jsp". The index page will be displayed.

Enter the user name and submit the form. Hello user name message will be displayed.

You can download the Struts 2 Hello World example by clicking the download link.

Source :Download

Source + Lib :Download