java如何在API中返回单例列表？

Question

我正在学习使用Eclipse IDE和Spring Boog框架创建java API。因此，我面临一个我无法解决的语法问题。以下是我的代码供您参考：

package first.microservice.moviecatalogservice.resources;

import java.util.Collections;
import java.util.List;

import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import first.microservice.moviecatalogservice.models.CatalogItem;

@RestController 
@RequestMapping("/catalog")
public class MovieCatalogResource {
        
    @RequestMapping("/{user_id}")   
    public List<CatalogItem> getCatalog(@PathVariable("user_id") String user_id)
        {
            return Collections.singletonList(
                     <CatalogItem> new CatalogItem(name: "DonJon", desc: "Test", rating: 4)
                    );
        }
}

另一个具有CatalogItem类的代码：

package first.microservice.moviecatalogservice.models;

public class CatalogItem {

    private String Name;
    private String Desc;
    private int Rating;
    
    public CatalogItem(String name, String desc, int rating) {
        Name = name;
        Desc = desc;
        Rating = rating;
    }
    
    public String getName() {
        return Name;
    }
    public void setName(String name) {
        Name = name;
    }
    public String getDesc() {
        return Desc;
    }
    public void setDesc(String desc) {
        Desc = desc;
    }
    public int getRating() {
        return Rating;
    }
    public void setRating(int rating) {
        Rating = rating;
    }
    
    
}

我希望输入URL模式以显示要在浏览器上显示的catalogitem的硬编码值

我在以下行中遇到错误：

return Collections.singletonList(
                     <CatalogItem> new CatalogItem(name: "DonJon", desc: "Test", rating: 4)
                    );

错误说明：

The method singletonList(T) in the type Collections is not applicable for the arguments (CatalogItem)

Multiple markers at this line
    - Syntax error on token "<", invalid Expression
    - Syntax error on token ":", invalid     AssignmentOperator
    - name cannot be resolved to a variable
    - Syntax error on token ":", invalid     AssignmentOperator
    - desc cannot be resolved to a variable
    - Syntax error on token ":", invalid     AssignmentOperator
    - rating cannot be resolved to a variable

Answer 1

我希望您的getCatalog方法中存在编译时错误。请更改退货声明，如下所示：

public List<CatalogItem> getCatalog(@PathVariable("user_id") String user_id)
        {
            return Collections.singletonList(new CatalogItem("DonJon", "Test", 4));
        }

Answer 2

AFAIK Java不支持命名参数。所以这条线

<CatalogItem> new CatalogItem(name: "DonJon", desc: "Test", rating: 4)

将给出您面临的语法错误。换成

new CatalogItem("DonJon", "Test", 4)

它应该会起作用

Answer 3

在月食中

1. 点击Windows>；首选项，然后选择左侧的Maven
2. 选中“启动时下载存储库索引更新”框。
   • 或者，选中下载工件源和下载工件JavaDoc复选框
3. 点击OK。警告将不再出现
4. 重新启动Eclipse