Spring Boot：@ConfigurationProperties实现配置自动绑定

代码

​​pom.xml​​：

<?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 https://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>2.6.2</version>
    </parent>

    <packaging>jar</packaging>

    <groupId>com.kaven</groupId>
    <artifactId>springboot</artifactId>
    <version>0.0.1-SNAPSHOT</version>

    <name>springboot</name>
    <description>springboot</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.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>

配置类：

package com.kaven.springboot.config;

import lombok.Setter;
import lombok.ToString;

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

import java.util.List;
import java.util.Map;
import java.util.Set;

@ConfigurationProperties(prefix = "user")
@Setter
@ToString
public class UserProperties {
    private String username;
    private String password;
    private Set<String> hobbies;
    private Map<String, Integer> scores;
    private List<UserToken> userToken;
}

​​UserToken​​类：

package com.kaven.springboot.config;

import lombok.Setter;
import lombok.ToString;

@Setter
@ToString
public class UserToken {
    private String token;
}

接口：

package com.kaven.springboot.controller;

import com.kaven.springboot.config.UserProperties;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import javax.annotation.Resource;

@RestController
public class ConfigController {
    @Resource
    private UserProperties userProperties;

    @GetMapping("/config")
    public String getConfig() {
        return userProperties.toString();
    }
}

​​application.properties​​：

user.username="kaven"
user.password="itkaven"
user.hobbies[0]="A"
user.hobbies[1]="B"
user.hobbies[2]="C"
user.scores.mathematics=145
user.scores.english=80
user.user-token[0].token="A"
user.user-token[1].token="B"
user.user-token[2].token="C"

启动类：

package com.kaven.springboot;

import com.kaven.springboot.config.UserProperties;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.properties.EnableConfigurationProperties;

@SpringBootApplication
@EnableConfigurationProperties(value = {UserProperties.class})
//@ConfigurationPropertiesScan(basePackageClasses = {UserProperties.class})
public class SpringbootApplication {
    public static void main(String[] args) {
        SpringApplication application = new SpringApplication(SpringbootApplication.class);
        application.run(args);
    }
}

下面这两个注解都可以使得​​Spring Boot​​​基于被​​@ConfigurationProperties​​​注解修饰的类创建​​bean​​​，因此​​UserProperties​​实例可以自动注入到控制器中。

@EnableConfigurationProperties(value = {UserProperties.class})
@ConfigurationPropertiesScan(basePackageClasses = {UserProperties.class})

而​​@ConfigurationPropertiesScan​​注解还可以指定要被扫描的包数组。

@ConfigurationPropertiesScan(basePackages = {"com.kaven.springboot.config"})

启动应用，访问​​http://localhost:8080/config​​。

效果符合预期。

构造器绑定

​​Spring Boot​​​将配置文件中的配置自动绑定到配置类，无非就是通过反射等手段，创建配置类实例，而配置项需要绑定到配置类实例的属性，这一般通过属性的​​set​​​方法或者构造器来实现，上面的演示是通过​​set​​​方法来进行绑定，这是​​@Setter​​注解的效果。

@Setter

如果需要通过构造器将配置项绑定到配置类实例的属性，可以使用​​@ConstructorBinding​​注解。

package com.kaven.springboot.config;

import lombok.ToString;

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

import java.util.List;
import java.util.Map;
import java.util.Set;

@ConfigurationProperties(prefix = "user")
@ToString
@ConstructorBinding
public class UserProperties {
    private String username;
    private String password;
    private Set<String> hobbies;
    private Map<String, Integer> scores;
    private List<UserToken> userToken;

    public UserProperties(String username,
                          String password,
                          Set<String> hobbies,
                          Map<String, Integer> scores,
                          List<UserToken> userToken) {
        this.username = username;
        this.password = password;
        this.hobbies = hobbies;
        this.scores = scores;
        this.userToken = userToken;
    }
}

使用​​@ConstructorBinding​​注解修饰类的问题在于类中可能有多个构造器，如果出现这种情况就会有问题。

package com.kaven.springboot.config;

import lombok.ToString;

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

import java.util.List;
import java.util.Map;
import java.util.Set;

@ConfigurationProperties(prefix = "user")
@ToString
@ConstructorBinding
public class UserProperties {
    private String username;
    private String password;
    private Set<String> hobbies;
    private Map<String, Integer> scores;
    private List<UserToken> userToken;

    public UserProperties() {}

    public UserProperties(String username,
                          String password,
                          Set<String> hobbies,
                          Map<String, Integer> scores,
                          List<UserToken> userToken) {
        this.username = username;
        this.password = password;
        this.hobbies = hobbies;
        this.scores = scores;
        this.userToken = userToken;
    }
}

因为​​Spring Boot​​不知道调用哪个构造器。

可以将​​@ConstructorBinding​​注解修饰在构造器上。

package com.kaven.springboot.config;

import lombok.ToString;

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

import java.util.List;
import java.util.Map;
import java.util.Set;

@ConfigurationProperties(prefix = "user")
@ToString
public class UserProperties {
    private String username;
    private String password;
    private Set<String> hobbies;
    private Map<String, Integer> scores;
    private List<UserToken> userToken;

    public UserProperties() {}

    @ConstructorBinding
    public UserProperties(String username,
                          String password,
                          Set<String> hobbies,
                          Map<String, Integer> scores,
                          List<UserToken> userToken) {
        this.username = username;
        this.password = password;
        this.hobbies = hobbies;
        this.scores = scores;
        this.userToken = userToken;
    }
}

结合@PropertySource

​​SourceConfig​​类：

package com.kaven.springboot.config;

import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;

@Configuration
@PropertySource(value = "classpath:/static/user.properties")
public class SourceConfig {}

效果符合预期，​​@ConfigurationProperties​​实现配置自动绑定就介绍到这里，如果博主有说错的地方或者大家有不同的见解，欢迎大家评论补充。