SpringBoot入门三（java代码方式配置之使用@ConfigurationProperties实现Spring Boot配置文件配置项读取）

目的：能够使用@ConfigurationProperties实现Spring Boot配置文件配置项读取（对象中）和应用

分析：
需求：将配置文件中的配置项读取到一个对象中；
实现：可以使用Spring Boot提供的注解@ConfigurationProperties,该注解可以将Spring Boot的配置文件（默认必须application.properties或application.yml）中的配置项读取到一个对象中

实现步骤：

1.加入注解依赖（不加入依赖@ConfigurationProperties会报错）
2.创建配置项类（jdbcProperties类），在改类名上添加注解@ConfigurationProperties，就可以把配置文件读取到此类上.
3.将jdbc.properties修改名称为application.properties
4.将jdbcProperites对象注入到JdbcConfig
5.测试

===========================

1.加入注解依赖（不加入依赖@ConfigurationProperties会报错）

<?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>

    <!--SpringBoot父工程-->
    <parent>
        <artifactId>spring-boot-starter-parent</artifactId>
        <groupId>org.springframework.boot</groupId>
        <version>2.3.4.RELEASE</version>
    </parent>

    <groupId>org.cc8w</groupId>
    <artifactId>javaboot_test</artifactId>
    <version>1.0-SNAPSHOT</version>

    <!--java编译版本，父工程已经指定了这样的变量-->
    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <!--SpringBoot Web启动器(不用写版本跟随父版本)-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <!--在配置注解@ConfigurationProperties加的-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>

        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>1.1.20</version>
        </dependency>

    </dependencies>

</project>

2.创建配置项类（jdbcProperties类），在改类名上添加注解@ConfigurationProperties，就可以把配置文件读取到此类上.

package com.cc8w.config;


import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.context.properties.ConfigurationProperties;

/**
 * @ConfigurationProperties从application配置文件中读取配置项
 * prefix 表示配置项的前缀,配置了就不用写前缀了
 * 配置项类中的类变量必须要和前缀之后的配置项名称一致
 */

@ConfigurationProperties(prefix = "jdbc")
public class JdbcProperties {

    private String driverClassName;
    private String url;
    private String username;
    private String password;

    public String getDriverClassName() {
        return driverClassName;
    }

    public void setDriverClassName(String driverClassName) {
        this.driverClassName = driverClassName;
    }

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    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;
    }
}

3.将jdbc.properties修改名称为application.properties （略）

4.将jdbcProperites对象注入到JdbcConfig

package com.cc8w.config;

import com.alibaba.druid.pool.DruidDataSource;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;

import javax.sql.DataSource;

@Configuration
//@PropertySource("classpath:jdbc.properties")
@EnableConfigurationProperties(JdbcProperties.class)
public class JdbcConfig {
/* 上一个案例写的
    @Value("${jdbc.driverClassName}")
    private String driverClassName;
    @Value("${jdbc.url}")
    private String url;
    @Value("${jdbc.username}")
    private String username;
    @Value("${jdbc.password}")
    private String password;

    @Bean
    public DataSource dataSource(){
        DruidDataSource dataSource = new DruidDataSource();
        dataSource.setDriverClassName(driverClassName);
        dataSource.setUrl(url);
        dataSource.setUsername(username);
        dataSource.setPassword(password);
        return dataSource;
    }
*/


    @Bean
    public DataSource dataSource(JdbcProperties jdbcProperties){
        DruidDataSource dataSource = new DruidDataSource();
        dataSource.setDriverClassName(jdbcProperties.getDriverClassName());
        dataSource.setUrl(jdbcProperties.getUrl());
        dataSource.setUsername(jdbcProperties.getUsername());
        dataSource.setPassword(jdbcProperties.getPassword());
        return dataSource;
    }

}

5.目录结构和测试