GraphQL--springBoot java demo

GraphQL is a query language :

搭建server，供前端与后端使用的时候参考：howtoGraphQL
简单的语法学习： learn

GraphQL 是一个新的API标准，可以比Rest更有效的强大的灵活；它是由FaceBook开发并开源
API defines how a clientcan load data from a server.
Graph QL是一种都API的查询语言，不是数据库查询语言，比Rest更优越

GraphiQL An in-browser IDE for exploring GraphQL.

自己创建参看： readme

简单的搭建一个自己的server

参考 Getting started with GraphQL Java and Spring Boot

安装Java： download JDK1.8，然后安装JDK与JRE，配置环境变量
安装Gradle： download zip文件，解压到相关路径，并配置环境变量；参考install
显示如下便成功了：

gradle -v

Welcome to Gradle 5.6!

按照文档中的示例，创建spring app： https://start.spring.io/.
选择
--Gradle Project
--Java
--Spring Boot 2.1.x
--Group: com.graphql-java.tutorial
--Artifact: book-details
-- select Web.这个我自己选择的是

点击后，会生成一个项目文件的压缩包，直接解压到电脑中，然后倒入Idea IDE，注意导入后，自己去seeting中设置JDK与Gradle为自己电脑上安装的location
粘贴文档中的代码作者放在了github中
build 项目

代码分析

报错了：

在浏览器中输入： http://localhost:8080/graphql
显示的结果是：

Whitelabel Error Page
This application has no explicit mapping for /error, so you are seeing this as a fallback.

Tue Aug 27 14:59:09 CST 2019
There was an unexpected error (type=Bad Request, status=400).
Required String parameter 'query' is not present

在idea中显示如下：

"D:\Install\IdeaUI\IntelliJ IDEA 2019.2.1\jbr\bin\java.exe" -XX:TieredStopAtLevel=1 -noverify -Dspring.output.ansi.enabled=always -Dcom.sun.management.jmxremote -Dspring.jmx.enabled=true -Dspring.liveBeansView.mbeanDomain -Dspring.application.admin.enabled=true "-javaagent:D:\Install\IdeaUI\IntelliJ IDEA 2019.2.1\lib\idea_rt.jar=59523:D:\Install\IdeaUI\IntelliJ IDEA 2019.2.1\bin" -Dfile.encoding=UTF-8 -classpath 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-streams\1.0.2\323964c36556eb0e6209f65c1cef72b53b461ab8\reactive-streams-1.0.2.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\com.google.code.findbugs\jsr305\3.0.2\25ea2e8b0c338a877313bd4672d3fe056ea78f0d\jsr305-3.0.2.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\org.checkerframework\checker-qual\2.5.2\cea74543d5904a30861a61b4643a5f2bb372efc4\checker-qual-2.5.2.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\com.google.errorprone\error_prone_annotations\2.1.3\39b109f2cd352b2d71b52a3b5a1a9850e1dc304b\error_prone_annotations-2.1.3.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\com.google.j2objc\j2objc-annotations\1.1\ed28ded51a8b1c6b112568def5f4b455e6809019\j2objc-annotations-1.1.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\org.codehaus.mojo\animal-sniffer-annotations\1.14\775b7e22fb10026eed3f86e8dc556dfafe35f2d5\animal-sniffer-annotations-1.14.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\javax.annotation\javax.annotation-api\1.3.2\934c04d3cfef185a8008e7bf34331b79730a9d43\javax.annotation-api-1.3.2.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\com.fasterxml.jackson.datatype\jackson-datatype-jdk8\2.9.9\4b04126963103216c9c43b0f34bbc36315654204\jackson-datatype-jdk8-2.9.9.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\com.fasterxml.jackson.datatype\jackson-datatype-jsr310\2.9.9\a33df137557793b0404a486888dbe049f7abeeeb\jackson-datatype-jsr310-2.9.9.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\com.fasterxml.jackson.module\jackson-module-parameter-names\2.9.9\a92facb55a2538e7b2fe14294570a18b823ad431\jackson-module-parameter-names-2.9.9.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\org.yaml\snakeyaml\1.23\ec62d74fe50689c28c0ff5b35d3aebcaa8b5be68\snakeyaml-1.23.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\com.fasterxml.jackson.core\jackson-databind\2.9.9\d6eb9817d9c7289a91f043ac5ee02a6b3cc86238\jackson-databind-2.9.9.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\org.apache.tomcat.embed\tomcat-embed-websocket\9.0.22\45974d3443cc15ad9d10239d762d5e15759e6364\tomcat-embed-websocket-9.0.22.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\org.apache.tomcat.embed\tomcat-embed-core\9.0.22\79f39903498b28adacb18fe2ea046edd306295a6\tomcat-embed-core-9.0.22.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\org.apache.tomcat.embed\tomcat-embed-el\9.0.22\4da4b778b635a7e78ca7cd7288253e2e47b88a9f\tomcat-embed-el-9.0.22.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\javax.validation\validation-api\2.0.1.Final\cb855558e6271b1b32e716d24cb85c7f583ce09e\validation-api-2.0.1.Final.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\org.jboss.logging\jboss-logging\3.3.2.Final\3789d00e859632e6c6206adc0c71625559e6e3b0\jboss-logging-3.3.2.Final.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\com.fasterxml\classmate\1.4.0\291658ac2ce2476256c7115943652c0accb5c857\classmate-1.4.0.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\com.fasterxml.jackson.core\jackson-annotations\2.9.0\7c10d545325e3a6e72e06381afe469fd40eb701\jackson-annotations-2.9.0.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\com.fasterxml.jackson.core\jackson-core\2.9.9\bfff5af9fb8347d26bbb7959cb9b4fe9a2b0ca5e\jackson-core-2.9.9.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\ch.qos.logback\logback-core\1.2.3\864344400c3d4d92dfeb0a305dc87d953677c03c\logback-core-1.2.3.jar;C:\Users\Winfery_Wen\.gradle\caches\modules-2\files-2.1\org.apache.logging.log4j\log4j-api\2.11.2\f5e9a2ffca496057d6891a3de65128efc636e26e\log4j-api-2.11.2.jar com.graphqljava.tutorial.bookdetails.BookDetailsApplication

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.1.7.RELEASE)

2019-08-27 16:20:05.959  INFO 12308 --- [           main] c.g.t.b.BookDetailsApplication           : Starting BookDetailsApplication on EPCNSZUW0073 with PID 12308 (D:\springBoot\book-details\build\classes\java\main started by Winfery_Wen in D:\springBoot\book-details)
2019-08-27 16:20:05.960  INFO 12308 --- [           main] c.g.t.b.BookDetailsApplication           : No active profile set, falling back to default profiles: default
2019-08-27 16:20:06.639  INFO 12308 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2019-08-27 16:20:06.658  INFO 12308 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2019-08-27 16:20:06.659  INFO 12308 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.22]
2019-08-27 16:20:06.743  INFO 12308 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2019-08-27 16:20:06.749  INFO 12308 --- [           main] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 757 ms
2019-08-27 16:20:07.035  INFO 12308 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2019-08-27 16:20:07.178  INFO 12308 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2019-08-27 16:20:07.181  INFO 12308 --- [           main] c.g.t.b.BookDetailsApplication           : Started BookDetailsApplication in 1.444 seconds (JVM running for 1.923)
2019-08-27 16:21:15.060  INFO 12308 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring DispatcherServlet 'dispatcherServlet'
2019-08-27 16:21:15.060  INFO 12308 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Initializing Servlet 'dispatcherServlet'
2019-08-27 16:21:15.066  INFO 12308 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Completed initialization in 6 ms
2019-08-27 16:21:15.092  WARN 12308 --- [nio-8080-exec-1] .w.s.m.s.DefaultHandlerExceptionResolver : Resolved [org.springframework.web.bind.MissingServletRequestParameterException: Required String parameter 'query' is not present]

Resolution

follow the log
install GraphQL Playground; open new workspace and
use url: http://localhost:8080/graphql?query=%7B__schema%20%7B%20types%20%7Bname%7D%20%7D%7D

一下的结果是在浏览器的url中输入的结果
{"data":{
    "__schema":
        {"types":
        [
            {"name":"__TypeKind"},
            {"name":"__Field"},
            {"name":"Query"},
            {"name":"__Schema"},
            {"name":"__Type"},
            {"name":"__EnumValue"},
            {"name":"__DirectiveLocation"},
            {"name":"String"},
            {"name":"Int"},
            {"name":"Book"},
            {"name":"Author"},
            {"name":"ID"},
            {"name":"__InputValue"},
            {"name":"Boolean"},
            {"name":"__Directive"}
            ]
           }
        }
}

打开GraphQL playground后就能进行使用；但是只能使用他规定的query语句

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

return:

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

schema:

directive @defer on FIELD
type Author {
  id: ID
  firstName: String
  lastName: String
}

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

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

introspection

在该示例代码中，其实是使用了GraphQL的schema来定义了只能使用的query；其实就是使用了graphQL中的introSpection(自我检测)；我们定义了type，但是有时候我们并不知道里面包含了哪些type，这个时候我们就可以通过query： __schema来获取这个系统相关的信息：

{
  __schema {
    types {
      name
    }
  }
}

对应的结果就是

{
  "data": {
    "__schema": {
      "types": [
        {
          "name": "Query"
        },
        {
          "name": "Episode"
        },
        {
          "name": "Character"
        },
        {
          "name": "ID"
        },
        {
          "name": "String"
        },
        {
          "name": "Int"
        },
        {
          "name": "FriendsConnection"
        },
        {
          "name": "FriendsEdge"
        },
        {
          "name": "PageInfo"
        },
        {
          "name": "Boolean"
        },
        {
          "name": "Review"
        },
        {
          "name": "SearchResult"
        },
        {
          "name": "Human"
        },
        {
          "name": "LengthUnit"
        },
        {
          "name": "Float"
        },
        {
          "name": "Starship"
        },
        {
          "name": "Droid"
        },
        {
          "name": "Mutation"
        },
        {
          "name": "ReviewInput"
        },
        {
          "name": "__Schema"
        },
        {
          "name": "__Type"
        },
        {
          "name": "__TypeKind"
        },
        {
          "name": "__Field"
        },
        {
          "name": "__InputValue"
        },
        {
          "name": "__EnumValue"
        },
        {
          "name": "__Directive"
        },
        {
          "name": "__DirectiveLocation"
        }
      ]
    }
  }
}

而上面的例子中，其实输入的就是该query。
现在，我们需要知道哪些query是我们可以做的，当我们定义type系统的时候，我们需要指定所有query的起始type，这个时候需要使用introspection来帮我们得到：

所以query 是我们开始的类型；
查询某个type对象的信息

{
  __type(name:"Author"){
    name
    kind
    description
    
  }
}

{
  "data": {
    "__type": {
      "name": "Author",
      "kind": "OBJECT",
      "description": null
    }
  }
}

查询type内容中子域的type信息

{
  __type(name:"Author"){
    name
    kind
    fields{
      name
      type{
        name
        kind
      }
    }
    
  }
}

return

{
  "data": {
    "__type": {
      "name": "Author",
      "kind": "OBJECT",
      "fields": [
        {
          "name": "id",
          "type": {
            "name": "ID",
            "kind": "SCALAR"
          }
        },
        {
          "name": "firstName",
          "type": {
            "name": "String",
            "kind": "SCALAR"
          }
        },
        {
          "name": "lastName",
          "type": {
            "name": "String",
            "kind": "SCALAR"
          }
        }
      ]
    }
  }
}

创建一个GraphQL service就是通过定义type和field，然后为每一个type中的每一个field提供functions，例如:

type Query {
  me: User
}

type User {
  id: ID
  name: String
}

function Query_me(request) {
  return request.auth.user;
}

function User_name(user) {
  return user.getName();
}

一旦一个service开始运行（一般是web sevice上的url），这个服务器上就能发送query并执行，收到的query首先会被检查并确保所涉及的type都是正确的，然后运行代码中对应的函数来得到结果。
例如：

{
  me {
    name
  }
}