如何使用可用属性从json检索特定数据

I was asked to do a simple RESTful service using Go, that has to retrieve all the data about a particular book using its ID value.

type Book struct {
    ID     string  `json:"id"`
    Isbn   string  `json:"isbn"`
    Title  string  `json:"title"`
    Author *Author `json:"author"`
}

//Author struct
type Author struct{
    Firstname string `json:"firstname"`
    Lastname  string `json:"lastname"`
}

//variables

//slice-> variable link to array
var books []Book



// Get single book
func getBook(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "application/json")
    params := mux.Vars(r) // Gets params
    // Loop through books and find one with the id from the params
    for _, item := range books {
        if item.ID == params["id"] {
            json.NewEncoder(w).Encode(item)
            return
        }
    }
    json.NewEncoder(w).Encode(&Book{})
}

func main() {
    // r := mux.NewRouter()
    fmt.Println("hello api")
    //initialize mux router
    r := mux.NewRouter()
    //mock data
    books=append(books,Book{ID:"1",Isbn:"32123",Title:"Book   one",Author:&Author{Firstname:"J.K.", Lastname:"Rowling"}})
    books=append(books,Book{ID:"2",Isbn:"45434",Title:"Book two", Author:&Author{Firstname:"P.K.",Lastname:"Rowling"}})

    //router handler
    r.HandleFunc("/api/books",getBooks).Methods("GET")
    r.HandleFunc("/api/books/{id}",getBook).Methods("GET")
    r.HandleFunc("/api/books",createBook).Methods("POST")
    r.HandleFunc("/api/books/{id}",updateBook).Methods("PUT")
    r.HandleFunc("/api/books/{id}",deleteBook).Methods("DELETE")

    log.Fatal(http.ListenAndServe(":8080",r))    
}

expected output if i enter -> http://localhost:8080/api/books/1 this has to return me

{
    "id": "1",
    "isbn": "32123",
    "title": "Book one",
    "author": {
        "firstname": "J.K.",
        "lastname": "Rowling"
    }
}

instead, I'm getting nothing in my browser

I just format the code as below and it works fine (pay attention to WriteHeader function).

package main

import (
        "encoding/json"
        "fmt"
        "log"
        "net/http"

        "github.com/gorilla/mux"
)

type Book struct {
        ID     string  `json:"id"`
        Isbn   string  `json:"isbn"`
        Title  string  `json:"title"`
        Author *Author `json:"author"`
}

//Author struct
type Author struct {
        Firstname string `json:"firstname"`
        Lastname  string `json:"lastname"`
}

//variables

//slice-> variable link to array
var books []Book

// Get single book
func getBook(w http.ResponseWriter, r *http.Request) {
        w.Header().Set("Content-Type", "application/json")
        params := mux.Vars(r) // Gets params
        // Loop through books and find one with the id from the params
        for _, item := range books {
                if item.ID == params["id"] {
                        w.WriteHeader(http.StatusOK)
                        json.NewEncoder(w).Encode(item)
                        return
                }
        }
        w.WriteHeader(http.StatusNotFound)
        json.NewEncoder(w).Encode(&Book{})
}

func main() {
        fmt.Println("Listening on :8080")

        // initialize mux router
        r := mux.NewRouter()

        // mock data
        books = append(books, Book{ID: "1", Isbn: "32123", Title: "Book one", Author: &Author{Firstname: "J.K.", Lastname: "Rowling"}})
        books = append(books, Book{ID: "2", Isbn: "45434", Title: "Book two", Author: &Author{Firstname: "P.K.", Lastname: "Rowling"}})

        // router handler
        r.HandleFunc("/api/books/{id}", getBook).Methods("GET")

        log.Fatal(http.ListenAndServe(":8080", r))
}

After running the above program. The following command on the console:

curl 127.0.0.1:8080/api/books/1

returns:

{"id":"1","isbn":"32123","title":"Book one","author":{"firstname":"J.K.","lastname":"Rowling"}}

Finally, as a recommendation for implementing the ReST API with Golang, you can check here.