Shulou(Shulou.com)06/02 Report--

In this issue, the editor will bring you about how to use the source code to analyze the Struts2 request processing and process. The article is rich in content and analyzes and describes for you from a professional point of view. I hope you can get something after reading this article.

1.1 Struts2 request processing

1. The steps for processing a request in the Struts2 framework:

A) the client initiates a request to the Servlet container

B) according to the Web.xml configuration, the request first goes through the ActionContextCleanUp filter, which is an optional filter, which is very helpful for the integration of Struts2 and other frameworks (SiteMesh Plugin), mainly cleaning up the ActionContext and Dispatcher of the current thread

C) the request goes through plug-in filters, such as SiteMesh, etc, etc.

D) the request goes through the core filter FilterDispatcher and executes the doFilter method, in which the ActionMapper is asked to determine whether the request needs to call an Action

E) if ActionMapper decides that an Action needs to be called, ActionMapper returns an ActionMapping instance (which stores the configuration information of Action), creates an ActionProxy (Action proxy) object, and passes the request to the proxy object to continue processing

F) the ActionProxy object finds the Action class that needs to be called according to the configuration file of the ActionMapping and Configuration Manager query framework

G) when the ActionProxy object is created, an instance of ActionInvocation is created at the same time

H) the ActionInvocation instance is called using a naming pattern, which involves the call of the relevant interceptor (Intercepter) before and after the process of calling Action

I) once the Action is executed, the ActionInvocation instance is responsible for creating and returning Result according to the configuration in struts.xml. Result is usually a template of JSP or FreeMarker that needs to be represented, or it may be another Action chain

J) if you want to do something before returning Result, you can implement the PreResultListener interface, and PreResultListener can be implemented in Interceptor or Action

K) according to the Result object information, the user response information response is generated. The tags inherited in the Struts2 framework can be used in the process of generating the response, and ActionMapper will be involved again in this process.

2. Struts2 request processing diagram:

1.2Source code analysis of Struts2 request processing

When a user sends a request to Struts2, the doFilter () method of FilterDispatcher is called automatically, and the doFilter () method handles the request process, as follows:

1. Create a value stack object stack

two。 Create an Action context object

3. Re-encapsulate the request, this time return different objects depending on the type of content of the request:

If it is of type multipart/form-data, an object of type MultiPartRequestWrapper is returned, which serves for file upload, otherwise, an object of type StrutsRequestWrapper is returned. MultiPartRequestWrapper is a subclass of StrutsRequestWrapper, and both classes are implementations of the HttpServletRequest interface.

4. The ActionMapping object is obtained through actionMapper.getMapping (), and the configuration information of Action is stored in the ActionMapping object (configuration information of Action: name, namespace of Action, and method method to be called). The related code is shown in the following figure:

For the above code, the activity diagram is as follows:

5. If the getMapping () method returns that the ActionMapping object is null, FilterDispatcher assumes that the user request is not Action, and FilterDispatcher parses it first:

If the request starts with / struts, the packages initialization parameters configured in the web.xml file are automatically found, and FilterDispatcher treats the files under the packages parameter value package as static resources, that is, the contents of the files are displayed directly on the page.

If the resource requested by the user does not start with / struts-either a .jsp file or an .html file-it continues down the filter chain until the requested resource is reached.

6. If the getMapping () method returns a valid ActionMapping object, it is considered that an Action is being requested and the Dispatcher.serviceAction (request, response, servletContext, mapping) method is called.

For the above six steps, the related code is shown in the following figure:

For the above code, the activity diagram is as follows:

7. Request to enter the dispatcher.serviceAction (request,response,servletContext,mapping) method:

A) encapsulate the relevant object information into Map (such as HttpServletRequest, Http parameters, HttpServletResponse, HttpSession, ServletContext, ActionMapping and other object information), store it in the execution context Map, and return the execution context Map object extraMap

B) get the action namespace, name attribute, method attribute and other information stored in the mapping object

C) load and parse the Struts2 configuration file. If there is no artificial configuration, load struts-default.xml, struts-plugin.xml, struts.xml sequentially by default, parse and save the action configuration, result configuration and interceptor configuration to the config object, and return the file configuration object config

D) create a proxy object for user Action based on the execution context Map, action namespace, name attribute, method attribute, etc.

E) execute the Action proxy object proxy.execute () method and turn to the result

The code related to the above steps, as shown in the figure:

8. Execute the Action proxy object proxy.execute () method, which is executed by calling the invocation.invoke () method, as shown in the following figure:

9. Execute the invocation.invoke () method, which implements the recursive call to the interceptor and executes the execute () method of Action, and the code in the DefaultActionInvocation.invoke () method, as shown below:

In the above code, we do not see whether the interceptor's recursive call is actually controlled by the programmer. The implementation of recursive call is very simple:

A) first, take a look at the Interceptor API definition:

B) all interceptors must implement the intercept method, and the parameter of this method is ActionInvocation, so if you call invocation.invoke () in the intercept method, you will continue to find the next interceptor in Action's Intercepor list and call Intercepor recursively.

Log interceptor LoggingInterceptor in Struts2, as shown in the following figure:

C) the interceptor recursively invokes the activity diagram, as follows:

10. In the invocation.invoke () method, after executing the interceptor, action and getting the resultCode, it continues to execute the PreResultListener collection and generates the Result object to implement the PreResultListener interface. You can do some custom processing before returning the Result, as shown in the figure

Before returning Result, there are two common ways to implement custom processing through PreResultListener: one is implemented in Interceptor and the other in Action, as shown in the figure:

You can find that the above two methods are implemented through anonymous inner classes. In fact, another way is to implement the PreResultListener interface in the interceptor and implement the method beforeResult method. As shown in the following figure:

11. * to complete the user response by generating Result

Steps 1-11 above are used to analyze the complete process of Struts2 processing requests, and the related code calls the process, as shown in the following figure:

The above is the editor for you to share how to use the source code to analyze the Struts2 request processing and process, if you happen to have similar doubts, you might as well refer to the above analysis to understand. If you want to know more about it, you are welcome to follow the industry information channel.

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