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Implement browser servlet database interaction

2022-07-18 07:44:00 【Rong, who has to learn every day】

Catalog

1、 Create a new project module
2、 add to web modular
3、 Import jar package
4、 Add module dependencies
5、 Deploy Tomcat
- 5.1 The first way
- 5.2 The second way
6、 To configure Web Containers
- 6.1 The first method of configuration
- 6.2 The second method of configuration
7、 Create client's html Request file
8、 newly build JDBC Connect to the operation database
- 8.1 Database operation
- 8.2 Change user name and password
9、 newly build Servlet Components
10、 To configure servlet mapping
- 10.1 The first method
- 10.2 The second method
11、 Check whether the data can be successfully added to the database

1、 Create a new project module

stay project So let's make a new one module
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2、 add to web modular

Built in your module Right click to select add framework support
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3、 Import jar package

In the project project Create a new directory in , Name it lib Folder .
We can also put lib Create a new folder directly in WEB-INF Next , Such a bad place is this lib It can only be the current moudle exclusive . If there is a second moudle New... We need to repeat again lib .
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Connect what you want to use with the database jar Package import in , That is, copy and paste into lib Under the folder , Download here jar The package and database versions should be consistent ,java Connect mysql Download the driver package of

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stay lib Folder right click Add as Library

4、 Add module dependencies

Click on File - Project Structure , Perform the following steps to configure
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First import Tomcat Dependence and Lib rely on , It includes JSP and Servlet Need to use some API, as well as JDBC A library that connects to a database
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5、 Deploy Tomcat

5.1 The first way

After adding dependencies above , here Problems It will show a problem , Click on Fix Just fix it
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5.2 The second way

To Artifacts Delete this module before adding it again , The steps are as follows ：

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Be careful not to choose the wrong one Archive（ representative War package , Namely Web The package ）, Although there's nothing wrong ,Tomcat Will automatically decompress it for you , But it's better to choose the one above

After selecting, click OK , The project is deployed
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Don't forget to apply after completion , Click on Apply And then click OK That's all right.

6、 To configure Web Containers

Be careful ： Here is tomcat Server, No tomcatEE Server
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The first use here is to import Tomcat application , Choose all here Tomcat Just install the directory

Then jump to the deployment page , Add deployment

6.1 The first method of configuration

It's direct here Fix That's all right.
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6.2 The second method of configuration

In this way, if there are multiple items, you can add them selectively
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Then on this page , Change this file directory to a /, Set the jump later URL You can have one less layer of folders

① Fill in web Container name , It's usually tomcat+ Version number
② After Launch It means Tomcat After loading, the browser selected in the back will open by default URL Corresponding resources
③ Set up your URL Resources to address , Upper general Application context Set as a / , If so, set the link here directly as http://localhost:8080/add.html that will do , If you have no settings , The link set here has one more level of directory http://localhost:8080/ Your directory name /add.html

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Be careful ：

Here, if you haven't made any changes , If the URL is ：http://localhost:8080/ Your directory / , So it shows that we are visiting index.html（Tomcat At the end of the default welcome page ）, But you didn't write this resource , Will report 404（ Resource not found ） error .
We can go through <welcome-file-list> Tab to set the welcome page ( stay tomcat Of web.xml Set in , Or in your own project web.xml Set in )

And remember apply - ok That's all right.
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7、 Create client's html Request file

stay web Right click... Under the folder new One HTML file , Notice the new one here html The document is and WEB-INF In the same directory , Don't put the new file in WEB-INF Directory
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The file after construction is shown in the following figure

stay add.html Create a new form in

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <form action="add" method="post">
         name ：<input type="text" name="fname"/><br/>
         Price ：<input type="text" name="price"/><br/>
         stock ：<input type="text" name="fcount"/><br/>
         remarks ：<input type="text" name="remark"/><br/>
        <input type="submit" value=" add to " />
    </form>
</body>
</html>

Be careful ：

Null pointer or NumberFormatException . Because there is price and inventory ,
If the price is not available , As a result, you want to be right null Conduct Integer.parseInt() You're going to report a mistake .
The reason for the mistake is mostly because name=“price” There is a mistake here , It turns out that Servlet End or use request.getParameter(“price”) To get .（ No spaces , It has to be exactly the same ）

8、 newly build JDBC Connect to the operation database

In this one module Under the src Create a new package under the folder ,fruit Package placement is related to database connection interaction DAO Interface file 、 Implementation classes and fruit Fruits, etc , You can go to the official official account of shangsilicon Valley to reply JavaWeb To get relevant information , Just copy and paste it directly ,DAO The specific principle of implementation can be seen in my previous article （ Silicon Valley ）JDBC Always review
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That's it when it's built ：

8.1 Database operation

The default database here is enabled , And there are already fruit This form , If not , Click the following directory in the Shang Silicon Valley information to find fruitdb.sql Run it in the database , It will generate a fruitdb Database and fruit form , After this step, keep the database open
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8.2 Change user name and password

Pasted here BaseDAO The file is used directly in Java How to configure the four elements in the code , So we found BaseDAO file , Modify the user name and password to be your own user name and password （ If you don't modify this connection, you won't be able to connect to the database , After adding data in a while, the server will respond with 500 FALSE ）
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9、 newly build Servlet Components

We will be having atguigu Create a new servlets Folder , stay servlet Create a new folder AddServlet class , Inherit one HttpServlet class （ This class is in the Tomcat Inside servlet-api jar In the bag , So remember to import Tomcat rely on ）, And because we add.html The method defined in is post, So we're going to rewrite it doPost Method （ If it is not rewritten, it will report 405 error ）, At the same time through request Object to get the information sent by the user
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AddServlet The components are written as follows ：

package atguigu.servlets;

import atguigu.fruit.dao.FruitDAO;
import atguigu.fruit.dao.impl.FruitDAOImpl;
import atguigu.fruit.pojo.Fruit;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class AddServlet extends HttpServlet {
    
    // Respond to your http request , The client sends a... To the server http request , The server encapsulates it into a HttpServletRequest object 
    @Override
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
        String fname = request.getParameter("fname");

        String priceStr = request.getParameter("price");
        Integer price = Integer.parseInt(priceStr);

        String fcountStr = request.getParameter("fcount");
        Integer fcount = Integer.parseInt(fcountStr);

        String remark = request.getParameter("remark");

        FruitDAO fruitDAO = new FruitDAOImpl();
        boolean flag = fruitDAO.addFruit(new Fruit(0, fname, price, fcount, remark));

        System.out.println(flag ? " Add success ！" : " Add failure ！");
    }
}

Be careful ：

405 problem ： The currently requested method does not support . such as , Our form method=post , that Servlet Must correspond to doPost, Otherwise the newspaper 405 error .

10、 To configure servlet mapping

How do we put add This action is similar to AddServlet What about the correspondence , Just click the Add button on my side , Send to server , The server knows which component I want to use to process this information

10.1 The first method

stay module Under the module of web In the catalog WEB-INF Found in folder web.xml file , Set... In it servlet and servlet-mapping Tag for connection mapping
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The document is modified as follows ：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd" version="4.0">
    <servlet>
        <servlet-name>AddServlet</servlet-name>
        <servlet-class>com.atguigu.servlets.AddServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>AddServlet</servlet-name>
        <url-pattern>/add</url-pattern>
    </servlet-mapping>
</web-app>

Be careful ：

Among them url-pattern In order to / At the beginning , This can't be lost , Unknown cause .

xml File mapping process ：

1.   Request from user ,action=add
2.   In the project ,web.xml  Find  url-pattern = /add   ->  The first 12 That's ok 
3.   Find the first 11 Yes  servlet-name = AddServlet
4.   Find a peace  servlet-mapping  in  servlet-name  coincident  servlet ,  Find No 7 That's ok 
5.   Find the first 8 Yes  servlet-class -> com.atguigu.servlets.AddServlet
6.   The user sent post request （method=post） ,  therefore  tomcat Will execute  AddServlet  Medium doPost Method

10.2 The second method

Use annotations , No need to modify web.xml file , Directly in your AddServlet Class using annotations

@WebServlet(“/add”), This one in double quotation marks /add Just like your original url-pattern The contents in the label are consistent .

The code is as follows （ Only modify in the first line ）：

@WebServlet("/add")
public class AddServlet extends HttpServlet {
    
    // Respond to your http request , The client sends a... To the server http request , The server encapsulates it into a HttpServletRequest object 
    @Override
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
        String fname = request.getParameter("fname");

        String priceStr = request.getParameter("price");
        Integer price = Integer.parseInt(priceStr);

        String fcountStr = request.getParameter("fcount");
        Integer fcount = Integer.parseInt(fcountStr);

        String remark = request.getParameter("remark");

        FruitDAO fruitDAO = new FruitDAOImpl();
        boolean flag = fruitDAO.addFruit(new Fruit(0, fname, price, fcount, remark));

        System.out.println(flag ? " Add success ！" : " Add failure ！");
    }
}

Be careful ：

Choose one of the two ways , Otherwise, an error will be reported

11、 Check whether the data can be successfully added to the database

Click on debug Carry out commissioning and operation
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Tomcat Successfully deployed and Web After the container is successfully configured, the interface

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The resource interface to respond after successful operation ：

The database interface ：

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After writing something inside, click the Add button , Let's see what happens , A successful addition is the return 200 Status code for ,
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Now look at the database interface , Successful user database interaction .

At this time, the console prints and adds the word success （ There may be a garbled code problem here , stay servlet Code set settings in ）