Spring Boot中EC2实例查询接口如何返回规范JSON响应

你当前使用嵌套ArrayList返回数据，只会得到无字段含义的嵌套数组，调用方无法直接识别每个字段的意义，需要调整为结构化对象返回，序列化后就是带键名的规范JSON，具体调整步骤如下：

1. 定义EC2实例信息的结构化实体类 #

首先创建一个实体类存储EC2实例的对应属性，按需添加需要返回的字段即可：

// 可使用Lombok的@Data注解省略手动写构造、getter、setter的代码
public class Ec2InstanceInfo {
    private String instanceId;
    private String instanceType;
    private String state;
    // 还可以继续补充amiId、monitoringState等你日志中打印的字段

    public Ec2InstanceInfo() {}

    public Ec2InstanceInfo(String instanceId, String instanceType, String state) {
        this.instanceId = instanceId;
        this.instanceType = instanceType;
        this.state = state;
    }

    // 以下为Getter、Setter方法
    public String getInstanceId() { return instanceId; }
    public void setInstanceId(String instanceId) { this.instanceId = instanceId; }

    public String getInstanceType() { return instanceType; }
    public void setInstanceType(String instanceType) { this.instanceType = instanceType; }

    public String getState() { return state; }
    public void setState(String state) { this.state = state; }
}

2. 修改原接口的返回类型和逻辑 #

把原方法的嵌套ArrayList返回类型，改为存放实体类的List：

public List<Ec2InstanceInfo> getAllInstances() {
    boolean done = false;
    List<Ec2InstanceInfo> instances = new ArrayList<>();
    DescribeInstancesRequest request = new DescribeInstancesRequest();
    while (!done) {
        DescribeInstancesResult response = ec2Client.describeInstances(request);
        
        for (Reservation reservation : response.getReservations()) {
            for (Instance instance : reservation.getInstances()) {
                // 构造实体对象而非字符串列表
                Ec2InstanceInfo info = new Ec2InstanceInfo();
                info.setInstanceId(instance.getInstanceId());
                info.setInstanceType(instance.getInstanceType());
                info.setState(instance.getState().getName());
                instances.add(info);

                // 原有日志逻辑保留即可
                System.out.printf(
                        "Found instance with id %s, " +
                                "AMI %s, " +
                                "type %s, " +
                                "state %s " +
                                "and monitoring state %s",
                        instance.getInstanceId(),
                        instance.getImageId(),
                        instance.getInstanceType(),
                        instance.getState().getName(),
                        instance.getMonitoring().getState());
            }
        }
        request.setNextToken(response.getNextToken());
        if (response.getNextToken() == null) {
            done = true;
        }
        System.out.println("flag stats = "+done);
    }
    return instances;
}

3. 序列化得到规范JSON #

如果你用的是SpringBoot等自带JSON序列化的Web框架，接口直接返回上述List<Ec2InstanceInfo>，就会自动序列化为如下格式的响应：

[
  {
    "instanceId": "i-09xxxxxxf5b82",
    "instanceType": "t2.nano",
    "state": "running"
  },
  {
    "instanceId": "i-03ddxxxxx956d099",
    "instanceType": "t2.micro",
    "state": "running"
  }
]

如果没有使用自动序列化的框架，手动用Jackson、Gson等JSON工具序列化返回的List即可，以Jackson为例：

ObjectMapper objectMapper = new ObjectMapper();
String jsonResult = objectMapper.writeValueAsString(getAllInstances());

内容的提问来源于stack exchange，提问作者Amara