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Spring Boot：@ConfigurationProperties實作配置自動綁定

代碼

​

​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>

配置類：

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​

​類：

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"

啟動類：

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);
    }
}

下面這兩個注解都可以使得​

​Spring Boot​

​​基于被​

​@ConfigurationProperties​

​​注解修飾的類建立​

​bean​

​​，是以​

​UserProperties​

​執行個體可以自動注入到控制器中。

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

而​

​@ConfigurationPropertiesScan​

​注解還可以指定要被掃描的包數組。

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

啟動應用，通路​

​http://localhost:8080/config​

​。

Spring Boot：@ConfigurationProperties實作配置自動綁定

效果符合預期。

構造器綁定

​

​Spring Boot​

​​将配置檔案中的配置自動綁定到配置類，無非就是通過反射等手段，建立配置類執行個體，而配置項需要綁定到配置類執行個體的屬性，這一般通過屬性的​

​set​

​​方法或者構造器來實作，上面的示範是通過​

​set​

​​方法來進行綁定，這是​

​@Setter​

​注解的效果。

@Setter

如果需要通過構造器将配置項綁定到配置類執行個體的屬性，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​

​注解修飾類的問題在于類中可能有多個構造器，如果出現這種情況就會有問題。

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;
    }
}

因為​

​Spring Boot​

​不知道調用哪個構造器。

Spring Boot：@ConfigurationProperties實作配置自動綁定

可以将​

​@ConstructorBinding​

​注解修飾在構造器上。

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;
    }
}
Spring Boot：@ConfigurationProperties實作配置自動綁定

結合@PropertySource

​

​SourceConfig​

​類：

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 {}
Spring Boot：@ConfigurationProperties實作配置自動綁定
Spring Boot：@ConfigurationProperties實作配置自動綁定
spring boot java spring 構造器
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