Spring JDBC 抽象框架 core 包提供了 JDBC 模板类，其中 JdbcTemplate 是 core 包的核 心类，所以其他模板类都是基于它封装完成的，JDBC 模板类是第一种工作模式。 
      JdbcTemplate 类通过模板设计模式帮助我们消除了冗长的代码，只做需要做的事情（即 可变部分），并且帮我们做了固定部分，如连接的创建及关闭。 
      Spring Boot 自动配置了 JdbcTemplate 数据模板。

       JDBC 默认采用 org.apache.tomcat.jdbc.pool.DataSource 数据源，数据源的相关配置参考都封装在 org.springframework.boot.autoconfigure.jdbc.DataSourceConfiguration 类中。默认使 用 Tomcat 连接池，可以使用 spring.datasource.type 指定自定义的数据源类型。

<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.jdbctemplate</groupId>
    <artifactId>jdbctemplate</artifactId>
    <version>0.0.1-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.0.RELEASE</version>
        <relativePath /> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <!-- 声明项目配置依赖编码格式为 utf-8 -->
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <fastjson.version>1.2.24</fastjson.version>
    </properties>

    <dependencies>
        <!--Spring Data Jpa依赖 -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <!--mysql驱动 -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
            <version>8.0.13</version><!--$NO-MVN-MAN-VER$-->
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <optional>true</optional>
        </dependency>

        <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>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

server.port =8089
server.servlet.context-path=/

spring.datasource.url=jdbc:mysql://localhost:3306/springbootdb?serverTimezone=UTC&autoReconnect=true
spring.datasource.username=root
spring.datasource.password=admin
##spring.datasource.driver-class-name=com.mysql.jdbc.Driver
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver

spring.jpa.hibernate.ddl-auto=create-drop
spring.jpa.database=MySQL
spring.jpa.database-platform=org.hibernate.dialect.MySQL5InnoDBDialect
spring.jpa.show-sql=true

package com.tszr.jpa.entity;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name = "t_user")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;

    @Column(name = "username", unique = true, nullable = false, length = 64)
    private String username;

    @Column(name = "password", nullable = false, length = 64)
    private String password;

    @Column(name = "email", length = 64)
    private String email;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}

package com.tszr.jpa.dao;

import java.util.List;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;

import com.tszr.jpa.entity.User;

public interface UserRepository extends JpaRepository<User, Integer> {
    /* 相当于select * from t_user where username = ? and password = ? */
    public User findByUsernameAndPassword(String username, String password);

    @Query("select u from User u where u.username like %?1%")
    public List<User> getUserByUsername(@Param("username") String username);
}

package com.tszr.jpa.controller;

import java.util.List;
import java.util.Optional;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;
import org.springframework.web.bind.annotation.DeleteMapping;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.PutMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

import com.tszr.jpa.entity.User;
import com.tszr.jpa.dao.UserRepository;

@RestController
@RequestMapping("/users")
public class UserController {
    @Autowired
    private UserRepository userRepository;

    @PostMapping() // 添加
    public User saveUser(@RequestBody User user) {
//        response.setContentType("application/json;charset=UTF-8");
        return userRepository.save(user);
    }

    @DeleteMapping("/{id}") // 删除
    public void deleteUser(@PathVariable("id") int id) {
        userRepository.deleteById(id);
    }

    @PutMapping("/{id}")
    public User updateUser(@PathVariable("id") int userId, @RequestBody User user) {
        user.setId(userId);
        return userRepository.saveAndFlush(user);
    }

    @GetMapping("/{id}")
    public User getUserInfo(@PathVariable("id") int userId) {
        Optional<User> optional = userRepository.findById(userId);
        return optional.orElseGet(User::new);
    }

    @GetMapping("/list")
    public Page<User> pageQuery(@RequestParam(value = "pageNum", defaultValue = "1") Integer pageNum,
            @RequestParam(value = "pageSize", defaultValue = "10") Integer pageSize) {
        return userRepository.findAll(PageRequest.of(pageNum - 1, pageSize));
    }

    @GetMapping("/ops")
    public List<User> getOPs(String username) {
        return userRepository.getUserByUsername(username);
    }

    @PostMapping("/login")
    public User getPerson(String username, String password) {
        return userRepository.findByUsernameAndPassword(username, password);
    }
}

package com.tszr.jpa;

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

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}