SpringBoot系列: 与Spring Rest服务交互数据

不管是单体应用还是微服务应用, 现在都流行Restful风格,  下图是一个比较典型的使用rest的应用架构, 该应用不仅使用database数据源, 而且用到了一个Weather微服务, 另一方面, 该应用也是通过rest方式为web UI 或其他微服务应用提供服务.

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通过Postman 插件测试Rest接口
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之前使用postman 插件调试rest接口总报 415 Unsupported Media Type错误, 原因是: HEADERS中必须设置Content-type为application/json, 后台才能顺利接收到参数. 见下图截图. 
{
"timestamp": "2018-09-07T06:49:57.620+0000",
"status": 415,
"error": "Unsupported Media Type",
"message": "Content type 'text/plain;charset=UTF-8' not supported",
"path": "/books"
}

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与 Rest 服务交互的几个环节
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一. Spring 后台与其他Rest服务的数据交互
Spring 提供了 RestTemplate 类, 方便和其他Rest服务交互数据

二. 在web response中 返回 json 数据
对于Restful的视图方法, 其返回类型可以是 ResponseEntity<T> 或者 ResponseEntity<List<T>>, Spring会自动将返回值转换为json格式. 如果要输出多个对象的复合体json, 可以在java中定义一个Wrapper类组合多个Pojo类, 然后返回这个Wrapper对象即可.

三. 接收 web Request 中的 json 数据
视图方法的 @RequestBody 注释参数可以是Map类型, 也可以是Pojo类型. 如果是Pojo类型, Spring就自动完成json->object的转换, 如果是map类型, Spring就自动完成kv映射. 如果json数据是多个object的某种组合, 我们可以在java中定义一个Wrapper类组合多个Pojo类, 专门接收 Request 中的json数据.

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示例代码
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Pojo代码:

class Office {
    private String address;

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }
}

class Car {
    private String brand;

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }
}

/*
 * Boss 类是 Office 和 Office 类的组合
 */
class Boss {
    private Car car;
    private Office office;

    public Car getCar() {
        return car;
    }

    public void setCar(Car car) {
        this.car = car;
    }

    public Office getOffice() {
        return office;
    }

    public void setOffice(Office office) {
        this.office = office;
    }
}

Controller和主函数代码:

@SpringBootApplication
@RestController
public class Demo1Application {

    // 示例: 一个对象的json response
    // 测试url为 http://localhost:8080/oneOffice
    // 结果为 {"address":"address1"}
    @ResponseBody
    @RequestMapping(value = "/oneOffice", method = RequestMethod.GET)
    public ResponseEntity<Office> oneOffice() {
        Office office = new Office();
        office.setAddress("address1");
        return new ResponseEntity<Office>(office, HttpStatus.OK);
    }

    // 示例: 一个集合的json response
    // 测试url为 http://localhost:8080/offices
    // 结果为 [{"address":"address1"},{"address":"address2"}]
    @ResponseBody
    @RequestMapping(value = "/offices", method = RequestMethod.GET)
    public ResponseEntity<List<Office>> offices() {
        List<Office> offices = new ArrayList<Office>();
        Office office1 = new Office();
        office1.setAddress("address1");
        Office office2 = new Office();
        office2.setAddress("address2");
        offices.add(office1);
        offices.add(office2);
        return new ResponseEntity<List<Office>>(offices, HttpStatus.OK);
    }

    // 示例: 一个简单对象的 Post 示例
    // 测试url为 http://localhost:8080/offices
    // 提交的data为  { "address": "address1" }
    @RequestMapping(value = "/offices", method = RequestMethod.POST, consumes = "application/json")
    @ResponseBody
    public String createOffice(@RequestBody Office office) {
        if (office != null && office.getAddress() != null) {
            return "OK";
        } else {
            return "Empty";
        }
    }

    // 示例: 一个组合对象的 response 示例
    // 测试url为  http://localhost:8080/oneBoss
    // 结果为  {"car":null,"office":{"address":"address1"}}
    @RequestMapping(value = "/oneBoss", method = RequestMethod.GET)
    @ResponseBody
    public ResponseEntity<Boss> oneBoss() {
        Office office = new Office();
        office.setAddress("address1");
        Boss objectWrapper = new Boss();
        objectWrapper.setOffice(office);
        return new ResponseEntity<Boss>(objectWrapper, HttpStatus.OK);
    }

    // 示例: 一个组合对象的 Post 示例
    // 测试url为 http://localhost:8080/bosses
    // 提交的data为  {"car":null,"office":{"address":"address1"}}
    @RequestMapping(value = "/bosses", method = RequestMethod.POST, consumes = "application/json")
    @ResponseBody
    public String createBoss(@RequestBody Boss boss) {
        if (boss != null && boss.getOffice() != null
                && boss.getOffice().getAddress() != null) {
            return "OK";
        } else {
            return "Empty";
        }
    }

    public static void main(String[] args) {
        SpringApplication.run(Demo1Application.class, args);
    }
}

=========================
参考
=========================
https://www.leveluplunch.com/java/tutorials/014-post-json-to-spring-rest-webservice/
https://javabeat.net/rest-api-best-practices/
https://www.baeldung.com/building-a-restful-web-service-with-spring-and-java-based-configuration
截图来自: https://github.com/hamvocke/testing-microservices-ebook/blob/master/testing-microservices.adoc