Servlet fast foundation building

Catalog

Servlet Thread safety problem

Servlet Different mapping methods

Servlet Multipath mapping

Servlet Create time

Default Servlet

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• Servlet Thread safety problem

• because Servlet It's using The singleton pattern , That is, there is only one instance object in the whole application
• So we need to analyze whether the class members in this unique instance object are thread safe
• A browser represents a thread , Multiple browsers represent multiple threads
• It is reasonable to say that what we expect is that each browser should view its own user name , But the result is a mess of data in the browser
• therefore , It can be said that Servlet It's not thread safe
• solve ：
• Be careful when defining class members
• If it's shared , And will only be assigned at initialization time , If other times are obtained , Then there's no problem
• If it's not shared , Or it can be assigned a value every time it is used , Then we have to consider thread safety ; It can be defined as doGet or doPost Method or use the synchronization function

• Servlet Different mapping methods

• The first one is
• The specific name of the way
• The resource path to be accessed must be exactly the same as the mapping configuration
• http://localhost:8080/demo2/cpc
• 
• The second kind
• / start + The way of wildcards
• As long as it conforms to the directory structure , Don't worry about the ending
• http://localhost:8080/demo2/cpc/suibianxie
• 
• The third kind of
• wildcard + Fixed format ending way
• As long as it conforms to the fixed ending format , Regardless of the path ahead
• http://localhost:8080/demo2/tjtjtj.cpc
• 
• Be careful ： Priority questions
• The more specific the priority, the higher , The more fuzzy it is, the lower the priority it has
• The first one is > The second kind > The third kind of

• Servlet Multipath mapping

• You can give Servlet Configure multiple access maps , So different functions can be realized according to different request paths
• Scene analysis ：
• If the access resource path is /vip
• The price of the goods hit 9 fold
• If the access resource path is /svip
• The price of the goods hit 5 fold
• If the accessed resource path is another
• There is no discount on the price of goods
• Code implementation
• getRequestURI() Method
• getRequestURI() Method returns a string , The content is the whole access url Of path Content , No query;
• example ： Input url The address is http://localhost:8080/testproject/test
• getRequestURI() return /testproject/test, For one String
• To configure
• Use the second
• / start + The way of wildcards
• 
• Code
• 
• test
• http://localhost:8080/demo2/cpc/vip
• 
• http://localhost:8080/demo2/cpc/svip
• 
• http://localhost:8080/demo2/cpc
• 

• Servlet Create time

• Create... On first visit
• advantage ： Reduce the waste of server memory ; Improve the efficiency of server startup
• disadvantages ： If there are some initialization operations to be done when the application is loaded , Cannot complete
• Created when the server loads
• advantage ： Create objects ahead of time , Improve the efficiency of first time execution ; You can complete some initialization operations when loading applications
• disadvantages ： It takes up a lot of server memory , It affects the efficiency of server startup
• To be modified Servlet Create a time ：
• Will be in <servlet> In the label , add to <load-on-startup> label
• Write an integer
• A positive integer represents the number created when the server loads , The smaller the value. , The higher the priority
• A negative integer or no write represents the first access to create

• Default Servlet

• Default Servlet It's one provided by the server Servlet
• It's configured in Tomcat Of conf In the directory web.xml in
• Its mapping path is <url-pattern>/<url-pattern>
• When we send a request , First of all, it will be in our project web.xml Find mapping configuration in , If found, execute
• But when we can't find the corresponding Servlet When the path
• Just go to the default Servlet, By default Servlet Handle
• therefore , Everything is Servlet
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