Advance d usage of Spr ing Boot

SpringBoot configuration file description

About the configuration file description

Explanation: When the Spring program st arts, it needs to load the default configuration file, the default name: application.properties

Modify character set encoding

Note: The following operations modify the character set format when parsing code in IDEA

properties configuration file description

grammar:

​ 1. Data structure key-value structure
​ 2. Writing key=value “key2”=“value2”
​ 3. Data type The data types of properties are all strings, so there is no need to add a ""
​ 4. Disadvantages The configuration information has no hierarchical structure, and the full name of the configuration must be written
​ 5. When the program loads the pro file through the IO stream, the default character set encoding IS0-8859-1

YML configuration file description

#About YML configuration file description
# 1. Data structure key=value
# 2. Data types are strings by default. If type conversion is required, the framework has already completed it internally
# 3.yml writing: 1.key: (space )  value 2. There is a hierarchical structure, pay attention when editing
# 4. Character set encoding: The default program loading is UTF-8
server:
  port: 8080
  #project release path
  servlet:
    #  /default localhost:8080/jt/xxxx request path
    context-path: /

SpringBoot assign s a property

Business description

Note: because the business needs some attribute information, if it is written directly in the code, the later of expansion is not good, so dynamic assignment is required. Since objects are generally managed by Spring container, the assign of operation should also have Spring container assign ment

Edit the YML configuration file

server:
  port: 8080
  # project release path
  server:
  	# / default localhost:8080/jt/xxxx request path
    context-path: /
# 2. Assign the attribute hello to represent the prefix key=hello.msg
hello:    
	msg: "Hello SpringBoot"

assign a value to a property

@RestController	//Returns a specially formatted string of JSON to the front end
public class HelloController{
    
    //Requirement: get attribute data from container springel=spel expression
    @Value("${hello.msg }")	//Automatically generate get/set methods
    private String msg ; //  = "Hello SpringBoot"
}

hot deployment

explain

​ Note: Hot deployment is generally more applicable in the development phase, but this function is generally canceled in the release phase.

​ Function: When the program is modified for a period of time, the tomcat server will automatically restart

​ Disadvantages: Eclipse is compatible with perfect restart immediately, IDEA restarts after 3~5 seconds

Add hot deployment jar package

CV import in the project's pom.xml file

<!--Support hot deployment -->
<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-devtools</artifactId>
</dependency>

Modify IDEA configuration

Description: In order to allow IDEA to automatically hot deploy

Key combination: ctrl + alt + shift + /

[External link image transfer failed, the source site may have an anti-leech mechanism, it is recommended to save the image and upload it directly (img-6jUmuCZp-1622595282808)(C:\Users\MTA\AppData\Roaming\Typora\typora-user-images\ image-20210527114331281.png)]

[External link image transfer failed, the source site may have an anti-leech mechanism, it is recommended to save the image and upload it directly (img-1qnAvIqk-1622595282811)(C:\Users\MTA\Desktop...png)]

Lombok bag

Annotated automatic generation of Get, Set, toString

<!--	Annotated automatic generation Get，Set，toString  similar method	-->
		<dependency>
			<groupId>org.projectlombok</groupId>
			<artifactId>lombok</artifactId>
		</dependency>

Self-annotated meaning:

​ @Data is written on the specified class to automatically generate get, set, toString and other methods for the specified class

​ @Accessors(chain = true) enable chain loading

​ @NoArgsConstructor No-argument constructor

​ @AllArgsConstructor full parameter constructor

import database

Check if the database is available

Enter cmd in the DOS command window to open the command window and enter the command: mysql -u account -p password

Check database service items

Description: Sometimes an abnormal situation may occur when starting the computer, resulting in the mysql database service not starting normally, and the display effect indicates that the database connection is abnormal.

Check: Check if the MYSQL service item is available

Spring container

Explanation: Spring container = HashMap<k,v>

@Controller
public class HelloController{
}
// Instantiation: Reflection Mechanism

SpringBoot integrates MyBatis

Configure pom.xml file

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.jt</groupId>
    <artifactId>springboot_demo_2</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.5.0</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <name>springboot_demo_2</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <!--Support hot deployment -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
        </dependency>
        <!--	Annotated automatic generation Get，Set，toString  similar method	-->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

Prepare the main boot class

package com.jt;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class SpringBootRun {

    public stat  ic v  oid main(String[] args) {
        SpringApplication.run(SpringBootRun.class ); 
    }
}

Solution if the port is occupied after startup

Create an application.yml file in the resources package under module and enter the following code

server:  port: 8090  #8090 is the new port number that can be specified by yourself

Create pojo package

Create a subpackage in the main startup class

This package is used to store the instantiated object classes required by the program

[External link image transfer failed, the source site may have anti-leech mechanism, it is recommended to save the image and upload it directly (img-fACNIsat-1622595282813)(C:\Users\MTA\AppData\Roaming\Typora\typora-user-images\ image-20210527151923310.png)]

Add jar to pom.xml

Introduce database driver

<dependency>        <groupId>mysql</groupId>        <artifactId>mysql-connector-java</artifactId>        <scope>runtime</scope>        <version></version></dependency>

SpringBoot database connection

<dependency>        <groupId>org.springframework.boot</groupId>        <artifactId>spring-boot-starter-jdbc</artifactId></dependency>

Spring integrates Mybatis (temporarily)

<dependency>        <groupId>org.mybatis.spring.boot</groupId>        <artifactId>mybatis-spring-boot-starter</artifactId>        <version>2.1.4</version></dependency>

Create an application.yml file to import data source information

server:  port: 8090  servlet:    context-path: /spring:  datasource:    driver-class-name: com.mysql.jdbc.Driver    url: jdbc :mys  ql://127.0.0.1:3306/jtdb? Servertimezone=gmt%2b8&useunicode=true&characterencoding=utf8&autoreconnect=true&allowmultiqueries=true username: root \ pojo  mapper-locations: classpath:/mybatis/mappers/*. XML # enable hump mapping configuration: Map underscore to camel case: true

About Mybatis Summary

What is Mybatis?

Mybatis is the framework of the persistence layer, which mainly interacts with the database. Mybatis encapsulates JDBC internally.

Mybatis calls it a "semi-automated ORM framework"

JDBC source code

package cn.tedu.example.jdbc;import java.sql.*;import java.util.Scanner;/** * Test JDBC * used to connect the java program with the database, the purpose is to operate the database through java code * @author Cloud */public class TestJdbc extends JDBCUtils{    public static void main(String[] args) {//        //Normal method(); / /// SQL injection attack solution method2(); //// JDBC connection SQL,java exercise method1()// Query Wu Yangyang of all data method3() in the user table// Insert data into dept table method4(); }  private static void method4() { try { Class.forName("com.mysq l.jdb c.Driver"); Connecti on con = DriverManager.getConnect i on("jdbc : mysql : //localhost:3306 /jdbcte st","root","root"); String sql = "insert into dept(dname,loc) values(?,?)";  PreparedStatement ps = con.prepareStatement(sql ) ;  ps .setString ( 1,"Sales Department");  ps.setString(2,"Second Area"); // Specially execute SQL ps.executeUpdate(sql); }  catch (Cla ssNotFoundException | SQLException e) { e. prin tStac kT race ( ) ; }  finally { try { ps .close(); }  catch (SQLException throwables) { throwables.printStackTrace(); }  try { con.close(); }  catch (SQLException throwables) { throwa bles.  pri ntS tac kT ace ( ) ; } } }   pri va t e st atic voi d m et hod 3 ( ) { String g g g g [] s tr = { " jd b c :m y s q l: / / l o c a lho s t: 3 3 0 6 / j d bc t e s t " , " roo t ", " r o  ot " } ;  C onn ecti on c on n = JD BCUt ils .getConnection( str ) ;  String [ ] pw1 = { "Wu Yangyang " , " 123456 " } ;  String str1 = " select id , name e , pwd from user  where e e name = ? and pwd = ? " ;  JDBCUtils . getPreparedStatement ( str1 , pw1 ) ) ; } / * * *  Use JDBC to query the user table of data in the data library through Java * / private static void method1() {try {/ / register the driver jar package class. Forname ("com. Mysql. JDBC. Driver"); / / connect to the data library connection con = drivermanager. Getconnection (/ / domain name: server name: / / data library of port number / data library name "jdbc: mysql://lo Calhost:3306 /jdbctest ", / / data library account data library password" ro OT "," root "); //get the transmitter state ent st = con.Cr EA tstatement(); //e xecute the SQL s state NT string SQL =" select id, name, p w d from us e r w here r e na me = ' Wu Y ng ya ng' a nd p wd = ' 123 4 56 ' "  ; Resu ltSe t rs = s t.e e xe cute Que r y ( sql ) ) ) ) ; // Process | Parse the res ult set while e e ( rs . next( ) ) { String id = rs . getString ( 1 ) ; String  g na me = rs . getString g g ( 2 ) ; String pwd = rs . getString ( 3 ) ; System . out . println ( id+ " \ n " + name+ " \ n " + pwd ) ) ) ; } //  Release resources  rs . close ( ) ;  st . close ( ) ;  con . close ( ) ; }  catch ( ClassNotFoundException | SQLException e ) { e . printStackTrace ( ) ; } } / * * *  use JDBC query user table of data * / private static  void method ( ) { try { // 1 .Register the driver jar package Class.forName ( " com .mysql.jdbc.Driver " ) ; // 2 . Connect to the data library // getConnection ( 1 , 2 , 3 )   ​​​​​​​​​​​​​​​​​​​​​​​​1 is which data to connect to the library 2 is the username 3 is the password Connection con = DriverManager  manage r.ge tC onnection( //Pro toc ol: server name ://data l ibrary of end s log an/dat a library name "jd bc: mysql ://localhost :3306/ jdbctest" , " root " ,  " root") ;/ /  3 . Get the transmitter Statement st = con.createStatement ( ); //  4. Exe cute e SQL String sql = " select ect id, nam e , pwd from user whe re na me = ' j    ack ' and pwd  =   '123456'";  ResultSet rs = st.executeQuery(sql); //  5. Procedures sin g|par sing th e re sult set// tr AV erse all the numbers in the user table according to next() is used to determine if there is data.If there is no data, return false while (rs.next()) {string id = rs.getstring (1); string name = rs.getstring (2); string PWD = rs.getstring (3); system.Out.Println (id+ "\t" + name+ "\ T" + PWD);}a// 6 . Release resource rs . close ( ) ;  st . close ( ) ;  con . close  ( ) ; }  catch ( ClassNotFoundException | SQLException e ) { e. printStackTrace (); } } / * * *  SQL injection attack of solution * Yes It mean s tha t when the  e use r o n ly ente rs s d ata, the specia l of SQL * is i included , which results in only the name and no passwor d. You can an view all data * After the name is enter e d ,  Both value s ​​​​​​​​​​w ill ca  use SQL attack problems:  jack '  #  or jack' or '1 = 1 */public s tatic v oid method d d d2(){ Scanner sc = new Scanner(Syst e m .in ); //Solve SQL Injection Problems try { Class.forName("com.mysql.jdb c.Driver " ); String url = " jd bc : mysql : //l oca lho st : 330 6 / jdb cte st " ; String  name = " roo t " ; String pwd = " root "  ;  Connection c on = DriverMan a g er .ge tC connecti o n ( url , name , p w d ) ; //  here ?  call alled placeholder Str in g sql = " select id ,  name , pwd from user where name = ? and pwd = ? " ;  Prepare dStatement ps = con . prepareStatement( sql ) ;  ps .setString( 1 , sc . nextLine( ) ) ;  ps . setString( 2 , sc . nextLine( )  ) ;  ResultSet rs = ps .executeQuery( ) ;  while ( rs . next( ) ) { String id = rs. getString( 1 ); String name1 = rs .getString( 2 ) ; String g p wd1 = rs . ge tString(3 ) ; System . out . prin t l n( id + "\ t" + name 1 + " \t "+pw d 1 ); } //  6 .  Release capital source rs.close( );  ps .close();  con.close(); }  catch (ClassNotFoundException | SQLException e) { e.printStackTrace(); } // Expose SQL injection probl ems try { Class.forName(  " com.mysql.jdbc.Driver "); String url = " jdbc :mysql: // localhost : 3306 / jdbct es t " ; String name = " root " ; String pw d = " roo t " ; con = Drive e  rManager .get Connection( u rl , name, pwd ) ; State t s t = con.createStationionment ( ) ; System .out .pri ntl n ( " Plea se enter y ou r u s ern am e " ) ; St ring n = sc .next  Line  ( ) ;  System . o ut .pr int ln ( " P le ase enter r y our password " ) ;  String p = sc .nextLine ( ) ;  String sql = " select id , name , pwd from user er wh ere name =     '"+n+"'and pwd ='"+p+"'";  R resultSet rs = st .executeQuery (sql);  while (rs.next()){ String id = rs .getString(1); String name1 = rs.ge tString(2); S  tring pw d1 = rs.get String(3) ; System m m .out.print ln( i d+ "\t" + name1+ "\t" + pwd 1 ); } // 6. Release resou rce es s ou rc e  rs .close( ) ;  st .c l ose() ;  con .close( ); }  catch (Cla ssNotFoundException | SQLExc eption e ) { e.prin tStackTrace(); } } }

ORM idea

Object Relational Mapping (English: Object Relational Mapping, ORM for short, or O/RM, or O/R mapping), is a programming technology for implementing object oriented different programming languages type system of data conversion between. Effectively, it actually creates a Programming language The "virtual object database" used here. There are many free and paid ORM products available today, and some programmers prefer to create their own ORM tools.

Summary: Operate the database in an object-oriented way,

Difficulties: 1. Objects should form a one-to-one mapping with tables

​ 2. The properties in the object should map one-to-one with the fields in the table

Classification:

​ 1. Update operation: handwritten SQL, parameters are generally encapsulated in the form of objects, and then executed through #{attribute}

​ 2. Query operation: handwritten SQL, the result set is automatically encapsulated

Thinking: Why has Mybatis not implemented a fully automated ORM for so many years? ? ?

Reason: Mybatis believes that the execution efficiency of SQL written by yourself is the highest, and it is also more general, such as multi-table association.

Summary: performance issues, if fully automated, object-oriented will affect performance

expand

Fully automated ORM

user object (…) userMapper.insert(user); the program is automatically stored in the library, the configuration is cumbersome