附录B.1. 元数据格式

配置元数据位于jars文件中的META-INF/spring-configuration-metadata.json，它们使用一个具有"groups"或"properties"分类节点的简单JSON格式：

{"groups": [
    {
        "name": "server",
        "type": "org.springframework.boot.autoconfigure.web.ServerProperties",
        "sourceType": "org.springframework.boot.autoconfigure.web.ServerProperties"
    },
    {
        "name": "spring.jpa.hibernate",
        "type": "org.springframework.boot.autoconfigure.orm.jpa.JpaProperties$Hibernate",
        "sourceType": "org.springframework.boot.autoconfigure.orm.jpa.JpaProperties",
        "sourceMethod": "getHibernate()"
    }
    ...
],"properties": [
    {
        "name": "server.port",
        "type": "java.lang.Integer",
        "sourceType": "org.springframework.boot.autoconfigure.web.ServerProperties"
    },
    {
        "name": "server.servlet-path",
        "type": "java.lang.String",
        "sourceType": "org.springframework.boot.autoconfigure.web.ServerProperties",
        "defaultValue": "/"
    },
    {
          "name": "spring.jpa.hibernate.ddl-auto",
          "type": "java.lang.String",
          "description": "DDL mode. This is actually a shortcut for the \"hibernate.hbm2ddl.auto\" property.",
          "sourceType": "org.springframework.boot.autoconfigure.orm.jpa.JpaProperties$Hibernate"
    }
    ...
],"hints": [
    {
        "name": "spring.jpa.hibernate.ddl-auto",
        "values": [
            {
                "value": "none",
                "description": "Disable DDL handling."
            },
            {
                "value": "validate",
                "description": "Validate the schema, make no changes to the database."
            },
            {
                "value": "update",
                "description": "Update the schema if necessary."
            },
            {
                "value": "create",
                "description": "Create the schema and destroy previous data."
            },
            {
                "value": "create-drop",
                "description": "Create and then destroy the schema at the end of the session."
            }
        ]
    }
]}

每个"property"是一个配置节点，用户可以使用特定的值指定它。例如，server.port和server.servlet-path可能在application.properties中如以下定义：

server.port=9090
server.servlet-path=/home

"groups"是高级别的节点，它们本身不指定一个值，但为properties提供一个有上下文关联的分组。例如，server.port和server.servlet-path属性是server组的一部分。

注：不需要每个"property"都有一个"group"，一些属性可以以自己的形式存在。