如何使用 Spring 的 JdbcTemplate 连接一个简单的 MySql 数据库？

Posted 2023-02-19

【中文标题】如何使用 Spring 的 JdbcTemplate 连接一个简单的 MySql 数据库？

【英文标题】：How to use Spring's JdbcTemplate to connect to a simple MySql database?

【发布时间】：2015-05-08 06:08:42

【问题描述】：

我正在尝试使用 Spring 的 JdbcTemplate 类连接到基于 this 教程的简单 mysql 数据库。事实上，我使用了他们的项目设置：

pom.xml

    <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>test</groupId>
    <artifactId>jdbc-test</artifactId>
    <version>0.0.1-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.2.2.RELEASE</version>
    </parent>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.14.8</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

Lombok 依赖项适用于 getter 和 setter。

然后是Application类：

package test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.jdbc.core.JdbcTemplate;

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

    @Autowired
    JdbcTemplate jdbcTemplate;

    @Override
    public void run(String... arg0) throws Exception 
        System.out.println("Creating tables");
        jdbcTemplate.execute("drop table customers if exists");
        jdbcTemplate.execute("create table customers(" +
                "id serial, first_name varchar(255), last_name varchar(255))");
    

最后是客户 pojo：

package test;

import lombok.AllArgsConstructor;
import lombok.Data;

@Data
@AllArgsConstructor
public class Customer 
    private long id;
    private String firstName, lastName;

对于数据源配置，我的资源文件夹中有一个 application.properties 文件：

spring.datasource.url=jdbc:mysql://localhost:3306/test
spring.datasource.username=test
spring.datasource.password=test
spring.datasource.driver-class-name=com.mysql.jdbc.Driver

spring.jpa.database = MYSQL

spring.jpa.show-sql = true

spring.jpa.hibernate.ddl-auto = update
spring.jpa.hibernate.dialect = org.hibernate.dialect.MySQL5Dialect
spring.jpa.hibernate.naming_strategy = org.hibernate.cfg.ImprovedNamingStrategy

数据库已启动并正在运行，但 autowirig 似乎仍然无法正常工作。 这是我尝试运行它时遇到的异常：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'application': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.
BeanCreationException: Could not autowire field: org.springframework.jdbc.core.JdbcTemplate test.Application.jdbcTemplate; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException:
No qualifying bean of type [org.springframework.jdbc.core.JdbcTemplate] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations:
@org.springframework.beans.factory.annotation.Autowired(required=true)
        at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:334)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1202)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:537)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
        at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:303)
        at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:299)
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:755)
        at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:757)
        at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480)
        at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:686)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:320)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:957)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:946)
        at test.Application.main(Application.java:12)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
        at java.lang.reflect.Method.invoke(Unknown Source)
        at org.springframework.boot.loader.MainMethodRunner.run(MainMethodRunner.java:53)
        at java.lang.Thread.run(Unknown Source)
Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: org.springframework.jdbc.core.JdbcTemplate test.Application.jdbcTemplate; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException:
No qualifying bean of type [org.springframework.jdbc.core.JdbcTemplate] found for dependency: expected at least 1 bean which qualifies as autowire
candidate for this dependency. Dependency annotations: @org.springframework.beans.factory.annotation.Autowired(required=true)
        at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:561)
        at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88)
        at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:331)
        ... 21 common frames omitted
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [org.springframework.jdbc.core.JdbcTemplate] found for dependency: expected at least 1 bean which
 qualifies as autowire candidate for this dependency. Dependency annotations: @org.springframework.beans.factory.annotation.Autowired(required=true)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(DefaultListableBeanFactory.java:1301)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1047)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:942)
        at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:533)
        ... 23 common frames omitted

我觉得奇怪的是，如果我用 com.h2 数据库替换 mysql-connector-java 依赖项，它就可以正常工作（就像在 spring 示例中一样）。

我需要以不同的方式配置 mysql 数据源吗？ 有什么建议吗？

【问题讨论】：

请确保为您启用了DataSourceAutoConfiguration。在运行启动应用程序并查看日志时添加 --debug java 参数。

【参考方案1】：

在下面添加依赖：

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

这将自动配置数据源

【讨论】：

成功了！数据源已配置。然而，我发现了另一个错误：第一个 sql 语句必须是：create table if not exists customers 才能在 mysql 中工作。欢呼