Spring Boot自动配置实战

Spring Boot自动配置

Spring Boot可以在我们引入对应的jar包后进行和spring的自动配置；这是理解Spring Boot运作原理的关键。

Spring Boot关于自动配置的源码在spring-boot-autoconfigure-1.x.x.RELEASE.jar内，主要包含如下的配置

下面我们模仿Spring Boot的自动配置，自己写一个项目也具有这样的功能

开发环境

java.version=jdk8
spring-boot.version=1.5.2.RELEASE
os.version=win8.1
idea=Intellij 2017.3
apache.maven.version=3.3.1

实现步骤

我们实现一个当某个类存在的时候，自动配置这个类的Bean，并可将Bean的属性在application.properties中配置

新建一个maven项目，pom文件如下：

<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.knight</groupId>
    <artifactId>auto-config</artifactId>
    <version>1.0.0</version>
    <packaging>jar</packaging>

    <dependencies>
       <!--增加Spring Boot自身的自动配置作为依赖-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-autoconfigure</artifactId>
            <version>1.5.2.RELEASE</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>2.3.2</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

属性配置，代码如下：

package com.knight.spring_boot_starter_hello;

import org.springframework.boot.context.properties.ConfigurationProperties;

@ConfigurationProperties(prefix = "hello")
public class HelloServiceProperties {

    private static final String MSG = "world";

    private String msg = MSG;

    public static String getMSG() {
        return MSG;
    }

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }
}

这里使用了类型安全属性配置。在application.properties中通过hello.msg=来指定

判断依据类，当这个类存在时会自动配置这个Bean

package com.knight.spring_boot_starter_hello;

public class HelloService {
    private String msg;

    public String sayHello(){
        return "Hello "+msg;
    }

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }
}

自动配置类：

package com.knight.spring_boot_starter_hello;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
@EnableConfigurationProperties(HelloServiceProperties.class)
@ConditionalOnClass(HelloService.class) //判断HelloService这个类在类路径中是否存在，且当容器中没有这个bean的时候自动配置这个bean
@ConditionalOnProperty(prefix = "hello", value = "enabled", matchIfMissing = true)
public class HelloServiceAutoConfiguartion {

    @Autowired
    private HelloServiceProperties helloServiceProperties;

    @Bean
    @ConditionalOnMissingBean(HelloService.class)
    public HelloService helloService() {
        HelloService helloService = new HelloService();
        helloService.setMsg(helloServiceProperties.getMsg());
        return helloService;
    }
}

注册配置

若想自动配置生效，需要注册自动配置类。在sr/main/resources下创建META-INF/spring.factories,内容如下('\'为了换行使用)：

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
  com.knight.spring_boot_starter_hello.HelloServiceAutoConfiguartion

项目的整个结构如下图：


验证上面配置创建的自动配置是否可行，创建一个项目然后引入该项目pom.xml文件如下：

<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>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.2.RELEASE</version>
    </parent>

    <groupId>com.knight</groupId>
    <artifactId>auto-config-test</artifactId>
    <version>1.0.0</version>
    <packaging>war</packaging>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>com.knight</groupId>
            <artifactId>auto-config</artifactId>
            <version>1.0.0</version>
        </dependency>
    </dependencies>

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

创建一个Application类

package com.knight.ch6_5;


import com.knight.spring_boot_starter_hello.HelloService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@SpringBootApplication
public class Ch65Application {

    @Autowired
    private HelloService helloService;

    public static void main(String[] args) {
        SpringApplication.run(Ch65Application.class, args);
    }

    @RequestMapping("/")
    public String index() {
        return helloService.sayHello();
    }
}

访问结果如下：

测试通过application.properties自定义配置属性，在Resources 目录下新建一个application.properties文件，内容如下：

hello.msg=Spring Boot