第5节.Nacos中建造者设计模式的使用

一、建造者模式的定义

将一个复杂对象的构建与其表示分离，使得同样的构建过程可以创建不同的表示。

二、建造模式的使用场景

当一个类的构造函数参数个数超过4个，而且这些参数有些是可选的参数，考虑使用构造者模式。

建造者模式一般是链式调用。

三、Nacos中的使用位置

3.1、实例元数据信息构造

nacos中的注册实例的接口，对于接收到的实例信息，采用了InstanceBuilder这个类完成构造，避免这个定义多个构造函数导致的需求变化问题，InstanceBuilder类的使用代码如下所示：

public String register(@RequestParam(defaultValue = Constants.DEFAULT_NAMESPACE_ID) String namespaceId,
        @RequestParam String serviceName, @RequestParam String ip,
        @RequestParam(defaultValue = UtilsAndCommons.DEFAULT_CLUSTER_NAME) String cluster,
        @RequestParam Integer port, @RequestParam(defaultValue = "true") Boolean healthy,
        @RequestParam(defaultValue = "1") Double weight, @RequestParam(defaultValue = "true") Boolean enabled,
        @RequestParam String metadata, @RequestParam Boolean ephemeral) throws Exception {
    // 
    NamingUtils.checkServiceNameFormat(serviceName);
    checkWeight(weight);
  	// 使用构造者设计模式建造实例对象
    final Instance instance = InstanceBuilder.newBuilder().setServiceName(serviceName).setIp(ip)
            .setClusterName(cluster).setPort(port).setHealthy(healthy).setWeight(weight).setEnabled(enabled)
            .setMetadata(UtilsAndCommons.parseMetadata(metadata)).setEphemeral(ephemeral).build();
    if (ephemeral == null) {
        instance.setEphemeral((switchDomain.isDefaultInstanceEphemeral()));
    }
    instanceServiceV2.registerInstance(namespaceId, serviceName, instance);
    return "ok";
}

其中，InstanceBuilder类的代码如下，并采用了非内部类的方式进行定义：

public class InstanceBuilder {
    
    private String instanceId;
    
    private String ip;
    
    private Integer port;
    
    private Double weight;
    
    private Boolean healthy;
    
    private Boolean enabled;
    
    private Boolean ephemeral;
    
    private String clusterName;
    
    private String serviceName;
    
    private Map<String, String> metadata = new HashMap<>();
    
    private InstanceBuilder() {
    }
    
    public InstanceBuilder setInstanceId(String instanceId) {
        this.instanceId = instanceId;
        return this;
    }
    
    public InstanceBuilder setIp(String ip) {
        this.ip = ip;
        return this;
    }
    
    public InstanceBuilder setPort(Integer port) {
        this.port = port;
        return this;
    }
    
    public InstanceBuilder setWeight(Double weight) {
        this.weight = weight;
        return this;
    }
    
    public InstanceBuilder setHealthy(Boolean healthy) {
        this.healthy = healthy;
        return this;
    }
    
    public InstanceBuilder setEnabled(Boolean enabled) {
        this.enabled = enabled;
        return this;
    }
    
    public InstanceBuilder setEphemeral(Boolean ephemeral) {
        this.ephemeral = ephemeral;
        return this;
    }
    
    public InstanceBuilder setClusterName(String clusterName) {
        this.clusterName = clusterName;
        return this;
    }
    
    public InstanceBuilder setServiceName(String serviceName) {
        this.serviceName = serviceName;
        return this;
    }
    
    public InstanceBuilder setMetadata(Map<String, String> metadata) {
        this.metadata = metadata;
        return this;
    }
    
    public InstanceBuilder addMetadata(String metaKey, String metaValue) {
        this.metadata.put(metaKey, metaValue);
        return this;
    }
    
    /**
     * Build a new {@link Instance}.
     *
     * @return new instance
     */
    public Instance build() {
        Instance result = new Instance();
        if (!Objects.isNull(instanceId)) {
            result.setInstanceId(instanceId);
        }
        if (!Objects.isNull(ip)) {
            result.setIp(ip);
        }
        if (!Objects.isNull(port)) {
            result.setPort(port);
        }
        if (!Objects.isNull(weight)) {
            result.setWeight(weight);
        }
        if (!Objects.isNull(healthy)) {
            result.setHealthy(healthy);
        }
        if (!Objects.isNull(enabled)) {
            result.setEnabled(enabled);
        }
        if (!Objects.isNull(ephemeral)) {
            result.setEphemeral(ephemeral);
        }
        if (!Objects.isNull(clusterName)) {
            result.setClusterName(clusterName);
        }
        if (!Objects.isNull(serviceName)) {
            result.setServiceName(serviceName);
        }
        result.setMetadata(metadata);
        return result;
    }
    
    public static InstanceBuilder newBuilder() {
        return new InstanceBuilder();
    }
}

通过这个方法，可以看到将对象的构造过程封装为了单独的builder类。