Spring Boot读取yml配置信息到配置对象

       Spring Boot允许配置外部化，这样同样的代码可以运行在不同的环境中，比如生产环境、测试环境用同一套代码，但是连的数据库信息可以放在应用的外部。可以使用properties文件，ymal文件，环境变量和命令行参数来使得配置外部化。属性值可以通过@Value注入到bean中，或者通过Spring的环境变量拿到配置，也可以通过@ConfigurationProperties把配置项绑定到结构化对象上。

       @Value只能注入一些key-value形式的配置，比如properites文件中的配置。对于yml文件中比较复杂的配置，推荐用@ConfigurationProperties绑定到结构化的对象的属性上。

例如，将下面的yml文件中的内容绑定到java对象上：

spring:
  kafka:
    #对应字符串列表(属于"spring.kafka"配置组)
    #下面的配置，如bootstrap-servers不能写成bootstrap.servers，用点号分隔取不到值
    bootstrap-servers: ["192.168.1.204:9092","192.168.1.100:9092","192.168.1.200:9092"]
    #对应字符串列表(属于"spring.kafka"配置组)
    schema-registry-url:
       - "http://192.168.1.204:18081"
       - "http://192.168.1.100:18081"
       - "http://192.168.1.200:18081"

    #下面的这些配置属于"spring.kafka.producer"配置组
    producer:
       retries: 100000
       buffer-memory: 33554432 #这个属性将绑定到@ConfigurationProperties(prefix = "spring.kafka.producer")注解的类的bufferMemory字段
       enableIdempotence: false #写成驼峰式
       max-in-flight-requests-per-connection: 1 #横线连接
       batch_size: 16384 #下划线连接
       linger-ms: 10
       ACKS: "-1" #大写字母
       topic: "role_operation_dev"
    #下面的这些配置属于"spring.kafka.consumer"配置组
    consumer:
       auto-offset-reset: "earliest"
       enable-auto-commit: false
       group.id: "record-service" #错误示范，用点号分割是无法绑定到对象属性上的
       topics: ["role_operation_dev"]

几点需要说明的是：

• java对象属性用驼峰式命名，可以有初始值，要为字段提供setter方法，用于注入值。
• 属于一个配置组的，即在yml文件中在一个层次上的，要绑定在同一个对象属性上。
• yml中的key可以用"-"、"_"连接单词，或者单词之间驼峰式命名，key也可以用大写字母。但是不能用点号连接单词。

对应的配置对象代码如下：

package cn.*.config;

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

import java.util.ArrayList;
import java.util.List;

/**
 * Kafka生产者和消费者共同的配置
 * @author pilaf
 * @create: 2018-08-08 20:36
 */
@Configuration
@ConfigurationProperties(prefix = "spring.kafka")
public class KafkaCommonConfig {

    private List<String> bootstrapServers = new ArrayList<>();

    private List<String> schemaRegistryUrl;

    public List<String> getBootstrapServers() {
        return bootstrapServers;
    }

    public void setBootstrapServers(List<String> bootstrapServers) {
        this.bootstrapServers = bootstrapServers;
    }

    public List<String> getSchemaRegistryUrl() {
        return schemaRegistryUrl;
    }

    public void setSchemaRegistryUrl(List<String> schemaRegistryUrl) {
        this.schemaRegistryUrl = schemaRegistryUrl;
    }


    @Override
    public String toString() {
        return "KafkaCommonConfig{" +
                "bootstrapServers=" + bootstrapServers +
                ", schemaRegistryUrl=" + schemaRegistryUrl +
                '}';
    }
}

package cn.superid.config;

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

/**
 * @author pilaf
 * @create: 2018-08-09 09:15
 */
@Configuration
@ConfigurationProperties(prefix = "spring.kafka.producer")
public class KafkaProducerConfig {

    private int retries = Integer.MAX_VALUE;

    private int bufferMemory =33554432;

    private boolean enableIdempotence = true;

    private int maxInFlightRequestsPerConnection = 1;

    private int batchSize = 16384;

    private int lingerMs =1;

    private String acks = "all";

    private String topic;

    public int getRetries() {
        return retries;
    }

    public void setRetries(int retries) {
        this.retries = retries;
    }

    public int getBufferMemory() {
        return bufferMemory;
    }

    public void setBufferMemory(int bufferMemory) {
        this.bufferMemory = bufferMemory;
    }

    public boolean isEnableIdempotence() {
        return enableIdempotence;
    }

    public void setEnableIdempotence(boolean enableIdempotence) {
        this.enableIdempotence = enableIdempotence;
    }

    public int getMaxInFlightRequestsPerConnection() {
        return maxInFlightRequestsPerConnection;
    }

    public void setMaxInFlightRequestsPerConnection(int maxInFlightRequestsPerConnection) {
        this.maxInFlightRequestsPerConnection = maxInFlightRequestsPerConnection;
    }

    public int getBatchSize() {
        return batchSize;
    }

    public void setBatchSize(int batchSize) {
        this.batchSize = batchSize;
    }

    public int getLingerMs() {
        return lingerMs;
    }

    public void setLingerMs(int lingerMs) {
        this.lingerMs = lingerMs;
    }

    public String getAcks() {
        return acks;
    }

    public void setAcks(String acks) {
        this.acks = acks;
    }

    public String getTopic() {
        return topic;
    }

    public void setTopic(String topic) {
        this.topic = topic;
    }

    @Override
    public String toString() {
        return "KafkaProducerConfig{" +
                "retries=" + retries +
                ", bufferMemory=" + bufferMemory +
                ", enableIdempotence=" + enableIdempotence +
                ", maxInFlightRequestsPerConnection=" + maxInFlightRequestsPerConnection +
                ", batchSize=" + batchSize +
                ", lingerMs=" + lingerMs +
                ", acks='" + acks + '\'' +
                ", topic='" + topic + '\'' +
                '}';
    }
}

package cn.superid.config;

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

import java.util.List;

/**
 * @author pilaf
 * @create: 2018-08-08 14:11
 */
@Configuration
@ConfigurationProperties(prefix = "spring.kafka.consumer")
public class KafkaConsumerConfig {

    private String autoOffsetReset ="earliest";

    private boolean enableAutoCommit = false;

    private String groupId;

    private List<String> topics;

    public String getAutoOffsetReset() {
        return autoOffsetReset;
    }

    public void setAutoOffsetReset(String autoOffsetReset) {
        this.autoOffsetReset = autoOffsetReset;
    }

    public boolean isEnableAutoCommit() {
        return enableAutoCommit;
    }

    public void setEnableAutoCommit(boolean enableAutoCommit) {
        this.enableAutoCommit = enableAutoCommit;
    }

    public String getGroupId() {
        return groupId;
    }

    public void setGroupId(String groupId) {
        this.groupId = groupId;
    }

    public List<String> getTopics() {
        return topics;
    }

    public void setTopics(List<String> topics) {
        this.topics = topics;
    }

    @Override
    public String toString() {
        return "KafkaConsumerConfig{" +
                "autoOffsetReset='" + autoOffsetReset + '\'' +
                ", enableAutoCommit=" + enableAutoCommit +
                ", groupId='" + groupId + '\'' +
                ", topics=" + topics +
                '}';
    }
}

POM.xml文件中的依赖如下：

		<dependency>
			<groupId>org.springframework.bootgroupId>
			<artifactId>spring-boot-starterartifactId>
			<version>2.0.3.RELEASEversion>
			<optional>trueoptional>
		dependency>
		<dependency>
			<groupId>org.springframework.bootgroupId>
			<artifactId>spring-boot-configuration-processorartifactId>
			<optional>trueoptional>
		dependency>

在程序中打印绑定后的内容如下：

commonConfig=KafkaCommonConfig{bootstrapServers=[192.168.1.204:9092, 192.168.1.100:9092, 192.168.1.200:9092], schemaRegistryUrl=[http://192.168.1.204:18081, http://192.168.1.100:18081, http://192.168.1.200:18081]}
producerConfig=KafkaProducerConfig{retries=100000, bufferMemory=33554432, enableIdempotence=false, maxInFlightRequestsPerConnection=1, batchSize=16384, lingerMs=10, acks='-1', topic='role_operation_dev'}
consumerConfig=KafkaConsumerConfig{autoOffsetReset='earliest', enableAutoCommit=false, groupId='null', topics=[role_operation_dev]}

结合上面yml文件中的规则可以看到，不符合规则的group.id确实没绑定成功。

参考文章：

• https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-external-config.html
• https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-Configuration-Binding