GraphQL是一种从服务器检索数据的查询语言 ，可替代 REST SOAP gRPC 等 

GraphQL is a query language 
API defines how a client can load data from a server.


获取id为 book-1 的书籍的详细信息
{
  bookById(id: "book-1"){
    id
    name
    pageCount
    author {
      firstName
      lastName
    }
  }
}

查询指定ID的书籍
返回书的id，名字，页数和作者
对于作者，返回名字和姓氏


响应为JSON

{
  "bookById":
  {
    "id":"book-1",
    "name":"Java is good",
    "pageCount":221,
    "author": {
      "firstName":"hello",
      "lastName":"java"
    }
  }
}


GraphQL 特性  静态类型
GraphQL模式

type Query {
  bookById(id: ID): Book
}

type Book {
  id: ID
  name: String
  pageCount: Int
  author: Author
}

type Author {
  id: ID
  firstName: String
  lastName: String
}




Java 实现 GraphQL服务器的主要步骤
1. 定义GraphQL模式
2. 决定如何获取查询的实际数据


GraphQL  GraphQLSchema  DataFetcher




springboot 2.7.10
org.springframework.boot:spring-boot-starter-web
org.springframework.boot:spring-boot-starter-graphql

com/graphql-java/graphql-java/18.4/graphql-java-18.4.jar
com/graphql-java/java-dataloader/3.1.2/java-dataloader-3.1.2.jar


s.b.a.g.s.GraphQlWebMvcAutoConfiguration : GraphQL endpoint HTTP POST /graphql
o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8060 (http) with context path ''



postman  post 
http://127.0.0.1:8060/graphql


{
  bookById(id: "book-1"){
    id
    name
    pageCount
    author {
      firstName
      lastName
    }
  }
}

返回值

{
    "data": {
        "bookById": {
            "id": "book-1",
            "name": "Harry Potter and the Philosopher's Stone",
            "pageCount": 223,
            "author": {
                "firstName": "Joanne",
                "lastName": "Rowling"
            }
        }
    }
}


{
  bookById(id: "book-21"){
    id
    name
    pageCount
    author {
      firstName
      lastName
    }
  }
}


{
    "data": {
        "bookById": null
    }
}



使用参数

query($id:ID){
  bookById(id: $id){
    id
    name
    pageCount
    author {
      firstName
      lastName
    }
  }
}


GRAPHQL VARIABLES


{"id":"book-2"}




post

{
  "query":"{查询语句}"
  "variables":"{参数和参数值}"
}






例子代码
https://gitee.com/dyyx/work2024/tree/master/demo/graphql-java-demo

https://www.graphql-java.com/tutorials/getting-started-with-spring-boot

graphql入门 
https://graphql.github.io/learn/