Java 如何使用 Spring Boot 返回一组对象？

How to return a set of objects with Spring Boot?

提问by faoxis

I did a lessonabout Spring Bootand it works perfectly. But what if I want to return a set of objects ? I tried doing thisbut it doesn't work. How can I do it correctly ?

我做了一个关于Spring Boot它的课程，它完美地工作。但是如果我想返回一组对象呢？我试着做这个，但它不工作。我怎样才能正确地做到这一点？

With one object (it works):

使用一个对象（它有效）：

@RequestMapping("/greeting")
public Greeting greeting(@RequestParam(value="name", defaultValue = "World") String name) {
    return new Greeting(counter.incrementAndGet(),
            String.format(template, name));
}

With many objects (it doesn't work):

有很多对象（它不起作用）：

@RequestMapping(value = "/greeting", method = RequestMethod.GET, consumes = MediaType.APPLICATION_JSON_VALUE, produces = MediaType.APPLICATION_JSON_VALUE)
public @ResponseBody List<Greeting> greeting() {
    Greeting greeting1 = new Greeting(1, "One");
    Greeting greeting2 = new Greeting(2, "Two");
    List<Greeting> list = new ArrayList<>();
    list.add(greeting1);
    list.add(greeting2);
    return list;
}

采纳答案by g00glen00b

If you compare your original method to your newly made one (with a List), you'll notice a few differences.

如果您将原始方法与新制作的方法（带有List）进行比较，您会发现一些不同之处。

First of all, within the @RequestMappingannotation you're now using the properties consumesand produces. producesis not a problem here, because you are producing a response that should be JSON. Howeveryou're not consuming anything, so you should leave away the consumes.

首先，在@RequestMapping注释中，您现在正在使用属性consumes和produces。produces在这里不是问题，因为您正在生成一个应该是 JSON 的响应。但是你没有消耗任何东西，所以你应该离开consumes.

@RequestMapping(value = "/greeting", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)
public @ResponseBody
List<Greeting> greeting() {
    Greeting greeting1 = new Greeting(1, "One");
    Greeting greeting2 = new Greeting(2, "Two");
    List<Greeting> list = new ArrayList<>();
    list.add(greeting1);
    list.add(greeting2);
    return list;
}

As a sidenote, you might also notice that you used the @ResponseBodyannotation. Putting it here won't cause any errors, but it is not necessary, because if you followed the Spring tutorial correctly, you should have annotated your controller with @RestControllerand by doing that, you already tell Spring that it will use a response body.

作为旁注，您可能还会注意到您使用了@ResponseBody注释。把它放在这里不会导致任何错误，但它不是必需的，因为如果你正确地遵循了 Spring 教程，你应该已经注释了你的控制器，@RestController通过这样做，你已经告诉 Spring 它将使用响应主体。

回答by johnpili

Here is the code snippet I did for this. Remove the "consume" from your @RequestMapping annotation because you are not using that in your method.

这是我为此所做的代码片段。从 @RequestMapping 注释中删除“consume”，因为您没有在方法中使用它。

@RestController
public class GreetingsController
{
    @RequestMapping(value = "greetings", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)
    public @ResponseBody
    List<Greeting> greeting() {
        Greeting greeting1 = new Greeting(1, "One");
        Greeting greeting2 = new Greeting(2, "Two");
        List<Greeting> list = new ArrayList<>();
        list.add(greeting1);
        list.add(greeting2);
        return list;
    }

    public class Greeting
    {
        private String message;
        private int count;

        public Greeting(int count, String message)
        {
            this.count = count;
            this.message = message;
        }

        public String getMessage()
        {
            return message;
        }

        public void setMessage(String message)
        {
            this.message = message;
        }
    }
}

回答by Vipul Gulhane

Let Say we have list of CarDetails Pojo and we want to return them back

假设我们有 CarDetails Pojo 列表，我们想将它们返回

@RestController
public class CarDetailController {
  @GetMapping("/viewAllCarDetailList")
    public List<CarDetail> retrieveAllCarDetails() {
        List<CarDetail> contacts = new ArrayList<CarDetail>();

        CarDetail objt = new CarDetail();
        objt.setCarModel("hyundai");
        objt.setSubModel("I10");
        CarDetail objt2 = new CarDetail();
        objt2.setCarModel("hyundai");
        objt2.setSubModel("I20");        
        contacts.add(objt);
        contacts.add(objt2);
        return contacts;
    }
}
    public class CarDetails {

            private String carModel;
            private String subModel;
// Will haave Setter getter and hash code equls method
//and constructor
    }

This JSON will be output:-

此 JSON 将被输出：-

[
    {
        "carModel": "hyundai",
        "subModel": "I10"
    },
    {
        "carModel": "hyundai",
        "subModel": "I20"
    }
]