Day 1: servlet related knowledge (1)

Servlet knowledge 1
1. What is Servlet? What can we do?
Sun's component specification for expanding web server functionality (early CGI: Common Gateway Interface)
Extension:
The Web server itself has no computing capability, that is, it cannot process dynamic resource requests. Servlet can process dynamic resource requests.
Component specification:
A component is a software module that complies with specifications, completes certain functions, and can be separately deployed. Generally, it cannot run independently. It must be dependent on the container to run.
JSR: Java specification request
JCP: Java communication process
Container:
Is a program that provides the runtime environment of components and manages the runtime of components.
Servlet container:
Provides a servlet running environment and manages the servlet running cycle. Common web servers, such as Tomcat,
A servlet container is also a web server.
What can we do?
Servlet can only be developed in Java. servlet can be used as all the events that Java classes can do.
2. How to develop a Servlet?
Step 1: Write a Java class to implement the servlet interface or inherit the httpservlet class.
Step 2: Compile (dependent on servlet API)
Step 3: Package (define a specific directory structure, and put the corresponding bytecode, configuration file, and related jar files into the corresponding directory structure)
Appname (any name, usually called Application name)
WEB-INF (must be named by this name)
Classes (put the. Class file)
Lib (optional, put the. jar file)
Web. XML (deployment description file)
Step 4: deploy (put the result in step 3 to a specific directory, which is webapps for Tomcat)
Step 5: Start the server
Windows-> startup. Bat-> shutdown. bat
Linux-> startup. Sh-> shutdown. Sh
Started successfully: http: // localhost: 8080/
Step 6: Access Servlet
Http: // localhsot: 8080/appname/url-Pattern
3. How does the servlet run?
Assume that the following address is entered in the browser: http: // ip: Port/appname/servletname
Step 1: The browser connects to the server based on the IP address and port.
Step 2: the browser splits the request data into an HTTP request packet (including appname/servletname) based on the HTTP protocol)
Step 3: an instance of httpservletrequest will be created by a communication module (generally called the servlet engine) in the server.
(Httpservletrequest is actually an interface implemented by the server provider). This instance contains
Data. In addition, an instance of httpservletresponse is created.
Step 4: The server finds web. XML based on appname/url-pattern and finds the corresponding servlet class name based on the information. View the Servlet
There is no corresponding instance. If not, an instance is created. If yes, no existing instance is used. Next, call service ()
The code in the service method can obtain the data in the request through the method provided by httpservletrequest.
You can set the returned results through the method provided by httpservletrequest.
Step 5: The Servlet Engine obtains data from httpservletresponse, generates an HTTP response packet, and sends it to the browser.
4. Use myeclipse to develop Servlet
(1) install myeclipse
(2) development steps
Step 1: create a web project
Step 2: Write Java classes under SRC
Step 3: Configure servlet in Web. xml
Step 4: deploy
A. Let myeclipse manage Tomcat
Window-> preferences-> myeclipse-> servers-> tomcat-> Tomcat 6.x
B. Deployment
Step 5: Access
Http: // ip: Port/appname/url-Pattern
5. Web. xml file content
<? XML version = "1.0" encoding = "UTF-8"?>
<! -- The first line of the file must be the above information, indicating the XML file version and character encoding -->
<! -- The following is used to configure a web project -->
<Web-app version = "2.4"
Xmlns = "http://java.sun.com/xml/ns/j2ee"
Xmlns: xsi = "http://www.w3.org/2001/XMLSchema-instance"
Xsi: schemalocation = "http://java.sun.com/xml/ns/j2ee
Http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd>
<Servlet>
<Description> helloservlet </description>
<Display-Name> helloservlet </display-Name>
<! -- Generally the name used to define the servlet -->
<Servlet-Name> helloservlet </servlet-Name>
<! -- Full name of the servlet -->
<Servlet-class> ttwork. servlet. helloservlet </servlet-class>
</Servlet>
<Servlet>
...
</Servlet>

<Servlet-mapping>
<! -- Same as the name used by the servlet above -->
<Servlet-Name> helloservlet </servlet-Name>
<! -- Relative path when accessing servlet -->
<URL-pattern>/servlet/helloservlet </url-pattern>
</Servlet-mapping>
<Servlet-mapping>
...
</Servlet-mapping>

<Error-page>
<Error-code> 500 </error-code>
<Location>/error.html </location>
</Error-page>

<Welcome-file-List>
<Welcome-File> index. jsp </welcome-File>
</Welcome-file-List>
</Web-app>