10 struts2 java study notes

2010-10-28  来源:本站原创  分类:Java  人气:150 

Recently I have spare time Java Virtual Machine Research, the intern assigned to the project team inside, do not want it used to be free, and managed to find time to continue the topic post. I intend to end some of J2ee and then talk about the JVM and JavaScript, as long as I have summed up the latest study notes, will be used in a timely manner and to share. Java sincerely hope that the relationship with the love of my colleagues in the common progress of a large ... ...

The first, prepared to continue to talk about the topic last Struts-2, a brief review of a history of men: over time, Web application framework of constantly changing demand, resulting in a number of the next generation of Struts solution. Struts Ti which continue to adhere to MVC model based on the improvement, continue the successful experience of Struts. WebWork project was released in March 2002, and it has revolutionized the Struts framework to improve style, the introduction of many new ideas, concepts and features, but the Struts and the original code is not compatible. WebWork is a mature framework, after several major improvements and release. In December 2005, WebWork and Struts Ti decision merged, then the same time, Struts Ti renamed to Struts Action Framework 2.0, as the true next generation Struts.

See Struts-2 of the process flow:

1) Browser generates a request and submit the framework to deal with: According to decide which interceptor configuration, action classes and results.

2) request through a series of interceptors: According to the request interceptor to do the different levels of different treatments. This Struts-1 in the RequestProcessor class is very similar.

3) Call Action: action to generate a new instance, call the business logic methods.

4) call to produce results: match result class and call the generated instance.

5) Request to return again after a series of interceptors: the process can also be configured to reduce the number of interceptors

6) The request returns the user: to return from the control servlet, build Html.

Here it is clear that the scope does not exist FormBean package, directly obtained from the Action data. There is a Strut-2 configuration web.xml file:

<filter>

<filter-name> controller </ filter-name>

<filter-class> org.apache.struts.action2.dispatcher.FilterDispatcher </ filter-class>

</ Filter>

<filter-mapping>

<filter-name> cotroller </ filter-name>

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

</ Filter-mapping>

Noting the previous servlet into a filter, ActionServlet into FilterDispatcher, *. do to become a / *. filter configuration defines the name (for association) and the filter class. filter mapping to match the success of the request URI to call the filter. By default, the extension ". Action". This file is in default.properties the "struts.action.extension" attribute defined.

default.properties attribute definition file, the path through the classpath in the project contains a file named "struts.properties" file to set different property values. The Struts-2 in the default configuration file name struts.xml. 1 and 2 of the action because the extension was. Do and. Action, so it can co-exist side. We look at the action of a Struts-2 code:

public class MyAction {

public String execute () throws Exception {

/ / Do the work

return "success";

}

}

Obvious difference is no longer inherit any classes and interfaces, the return of just a String, without parameters. In fact, any Struts-2 free parameters to return String methods can be configured to call the action. Get all the parameters come from it? The answer is Inversion of Control Technology (Inversion of Control). The author as the most popular way to explain, we first tried to get the Action request object, which can extract any parameters submitted the page. Then we set the request of a member variable, then it needs a set method. As most of the action needs to do this, we set this method as interfaces.

public interface ServletRequestAware {

public void setServletRequest (HttpServletRequest request);

}

public class MyAction implements ServletRequestAware {

private HttpServletRequest request;

public void setServletRequest (HttpServletRequest request) {

this.request = request;

}

public String execute () throws Exception {

/ / Do the work directly using the request

return Action.SUCCESS;

}

}

Who will call the set method? Who will control the action that the behavior of the past, we are in the appropriate place to write their own on a action.setServletRequest (...), that is, control of the programmer here. However, the idea of Inversion of Control where calls to the container to determine the running, as long as the use of Java reflection to get Method object and call its invoke method of passing arguments can do so from the programmer control here transferred to the container side. Many programmers can reduce the tedious work of more focus on business logic. Request can be injected into action, the other can also be any object. Action of the member variables in order to ensure thread safety, Struts-2's action is not a single case, each new request will have a new action instance.

So one may ask, in the end who will do the object into the work? The answer is interceptors. Interceptor is what? I again try to explain the popular concept of interceptors. We have to understand the words of the interceptor, first we must understand the kinds of design patterns in GOF23 Proxy mode.

A object to calling f (), it is hoped that agent to do B, then B must be A reference to an object, then B's f () is called by A object reference object A f () method, and ultimately achieve A of f () is called purpose. Will anyone think this is very troublesome, why obviously as long as Af () can be completed must be packaged to B, f () method go? What are the benefits?

1) Here we have only one A, when we have a number of A, when B only need to monitor an object f () method can control all from the overall situation is called f () method.

2) Also, since an agent B to get A reference to an object, then B can determine the object in the real tune A f () method which can be done before the pre-work and get it done back to the previous post which may have to do the work.

This point, we see that the concept of interceptors that yet? It intercepts the next tone f () method of the request, and then make a unified treatment (can be different for each approach, analytical object A can be identified), processed and then released. This look like a cross-section of the river flows a knife, all the water molecules want to be searched and then released? This is the AOP (Aspect of Programming Aspect Oriented Programming) ideas.

Anyway, Struts-2 is the use of the AOP and IoC technology to reduce the coupling between action and framework, trying to maximize the re-action purposes. In such a technology motivated by, Struts-2's action by the framework into a simple to use POJO (Plain Old Java Object) nothing more. Practical thoughts on AOP and IoC has been out all over each new frame, they are not how new technologies are also using the JDK already can do the most to them is more representative of programming to an interface to improve reuse, increase the extension of an idea. Struts-2 is only part of the design using both thought to be completed, and the other is the fire in the framework of the recent Spring, to a greater extent represent the two design ideas, I will be the next one to further explore the structure of Spring.

PS: on the Struts-2 did not really how I used, here are some of the older generation saw the post after the online write your own learning experience, inadequate please forgive me!

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