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This article mainly introduces how to achieve a Servlet-based hello world program, the article introduces in great detail, has a certain reference value, interested friends must read it!

one。 Introduce related jar packages

First of all, let's create a Maven project in idea. Except for the path you want to fill in, you can next and finish all the way.

Once created, we need to add a set of tags to the pom.xml and introduce servlet api's jar package into the tags. The introduction method is to copy and paste from the maven central warehouse to maven the central warehouse.

After opening it, we type servlet in the search box, and the first one is the result we want.

We chose the Java Servlet API of the version number corresponding to Tomcat (the blogger's Tomcat version is 8, so we chose the version number 3.1.0)

At this point, we can directly copy the middle code into the tag we have created.

Note: at the beginning, the code may be red, indicating that maven is downloading resources. You only need to wait a while, or refresh it for a while, and then you can successfully introduce it.

two。 Write java code 1. Create a class

The code we created needs to be inherited from the HttpServlet class before it can be called by Tomcat. If the Maven dependency is downloaded incorrectly, the HttpServlet cannot be completed (marked red).

two。 Delete the super method / / super.doGet (req, resp); this method directly constructs an incorrect response (the response with a status code of 405), be sure to delete it

Add:

Protected void doGet (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException

DoGet is the method of the parent class HttpServlet. The parameters of this method are HttpServletRequest (HTTP request) and HttpServletResponse (HTTP response). All you need to do in the doGet method is to generate a response based on the request.

@ Override

After we rewrite the doGet here, we do not need to call doGet manually, but by Tomcat automatically; nor do we need to manually create HelloServlet instances, which are also automatically created by Tomcat.

3. Construct related strings

This operation is to write a "hello world" string to the body of the HTTP response.

4. Associate a class with a HTTP-specific request

Just now we have successfully constructed the relevant string, but we do not know what kind of request to send to execute the code of the HelloServlet class, so we need to associate the class with a HTTP-specific request by adding this note to the class:

Just associate with the url path according to the HTTP request

If our Tomcat receives a request with a path of / hello, the code to HelloServlet will be called

If the request is a GET request, the doGet method of HelloServlet is called

Similarly, if the request is a POST request, the doPost method of HelloServlet will be called

At this point, the complete code is shown above

three。 Create some necessary directories and files

If we want this program to run on Tomcat, it is not enough to rely on the directories and files created by Maven. We have to create some extra content ourselves.

First we create a new webapp directory under the main directory

Next, create a WEB-INF directory under the directory you just created

Then, we can create another xml file under the directory we just created (if it is a static page deployed on Tomcat, we do not need a xml file, but if it is servlet code, it is necessary for Tomcat to recognize it)

Archetype Created Web Application

Finally, we can just write these things in.

four。 Packaging program

After completing the above steps, we need to compile our current code and generate a compressed package. At this point, we can continue to complete it through maven because the package we typed through maven is in jar format, Tomcat cannot directly recognize the package in jar format, jar package is usually run using the java-jar command, and the format recognized by Tomcat is war, so we should break it into a package in war format.

We can manually modify it directly in pom.xml.

At this point, double-click directly and you can pack.

The results are shown above.

When the war package is deployed to tomcat, tomcat will automatically extract it to generate a directory with the same name.

Later, when you access the webapp through the browser URL, put the name of the directory in the URL.

So we'd better change to a simpler name so that we can visit it.

At this point, the blogger sets the name to servlet1.

At this point, we can continue to package and generate the package we want to name.

five。 Deployment program

After packing the package, we can deploy the generated war package to Tomcat (copy the war package to the webapps directory of Tomcat)

Then after we start Tomcat, we will generate a directory with the same name as the war package under webapps

The web.xml and the .class file generated after compilation are included in WEB-INF.

META-INF contains third-party jar packages that are currently dependent on webapp

six。 Verify that the program is working properly

When all the previous steps have been completed, we can verify that we only need to access Tomcat through the browser, construct a specific request, and trigger it to the specific code.

The above is all the contents of the article "how to implement a hello world program based on Servlet". Thank you for reading! Hope to share the content to help you, more related knowledge, welcome to follow the industry information channel!

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