Welcome resource files
premise:
The user can remember the name of the website, but not the file name of the website resource
The default welcome resource file:
When the user sends a [default request] for a certain website,
At this time, the resource file automatically returned from the current website by the Http server
Normal request: http://localhost:8080/myWeb/index.
Default request: http://localhost:8080/myWeb/
Tomcat's locating rules for default welcome resource files
1) Rule location: Tomcat installation location/conf/web.xml
2) Rule order:
<welcome-file-list>
<welcome-file>index.html</w
<welcome-file>index.htm</we
<welcome-file>index.jsp</we
</welcome-file-list>
Set the default welcome resource file rule for the current website
1) The location of the rule/web/WEB-INF/web.xml
2) Rule order:
<welcome-file-list>
<welcome-file>user_Login.html</welcome-file>
</welcome-file-list>
2) The website has set a custom default file location rule, at this time the location rule that comes with Tomcat will be invalid.
Http status code
Introduction:
1) A symbol composed of three digits
2) Before the Http server pushes the response packet, it will process the request according to the situation
Write the Http status code to the [status line] in the response packet
3) If the Http server returns the corresponding resource file for this request.
Inform the browser how to handle this result through the Http status code
If the Http server is unable to return the corresponding resource file for this request
Explain to the browser the reason why the service cannot be provided through the Http status code
classification:
1) Composition: 100-599: divided into five categories
2）1xx：
The most characteristic:
100: Notify the browser of the resource file returned this time
It is not an independent resource file, it needs the browser to accept
After responding to the package, continue to ask the Http server for other resource files that it depends on
3）2xx：
The most characteristic:
200: Notify the browser that the resource file returned this time is a
Complete and independent resource files, the browser does not need to ask for it after receiving it
Other related files
4）3xx：
The most characteristic:
302: Notify the browser that what is returned this time is not the content of a resource file
It is the address of a resource file, and the browser needs to automatically initiate a request based on this address
Request this resource file
response.sendRedirect("the address of the resource file"); write the location in the response header
And this behavior causes Tomcat to write 302 to the status line
5）4xx：
The most characteristic:
404: Notify the browser that the resource file to be accessed is not located in the server
So unable to provide relevant help
405: Notify the browser that the accessed resource file (Servlet) has been located in the server
But this Servlet cannot handle the request method used by the browser
6）5xx：
The most characteristic:
500: Notify the browser that the accessed resource file (Servlet) has been located in the server
This servlet can receive the request method used by the browser, but the servlet is processing the request
During the period, it failed due to a Java exception.