我有以下JSON文本。我如何解析它以获得pageName, pagePic, post_id等的值?
{
"pageInfo": {
"pageName": "abc",
"pagePic": "http://example.com/content.jpg"
},
"posts": [
{
"post_id": "123456789012_123456789012",
"actor_id": "1234567890",
"picOfPersonWhoPosted": "http://example.com/photo.jpg",
"nameOfPersonWhoPosted": "Jane Doe",
"message": "Sounds cool. Can't wait to see it!",
"likesCount": "2",
"comments": [],
"timeOfPost": "1234567890"
}
]
}
主要有两种选择……
Object mapping. When you deserialize JSON data to a number of instances of:
1.1. Some predefined classes, like Maps. In this case, you don't have to design your own POJO classes. Some libraries: org.json.simple https://www.mkyong.com/java/json-simple-example-read-and-write-json/
1.2. Your own POJO classes. You have to design your own POJO classes to present JSON data, but this may be helpful if you are going to use them into your business logic as well. Some libraries: Gson, Jackson (see http://tutorials.jenkov.com/java-json/index.html)
映射的主要缺点是它会导致大量内存分配(以及GC压力)和CPU占用。
面向流的解析。例如,Gson和Jackson都支持这种轻量级解析。另外,您还可以查看一个自定义的、快速的、无gc的解析器示例https://github.com/anatolygudkov/green-jelly。在需要解析大量数据和对延迟敏感的应用程序中,更倾向于使用这种方式。
您可以使用DSM流解析库来解析复杂的json和XML文档。DSM只解析一次数据,不会将所有数据加载到内存中。
假设我们有一个Page类来反序列化给定的json数据。
页面类
public class Page {
private String pageName;
private String pageImage;
private List<Sting> postIds;
// getter/setter
}
创建一个yaml Mapping文件。
result:
type: object # result is array
path: /posts
fields:
pageName:
path: /pageInfo/pageName
pageImage:
path: /pageInfo/pagePic
postIds:
path: post_id
type: array
使用DSM提取字段。
DSM dsm=new DSMBuilder(new File("path-to-yaml-config.yaml")).create(Page.class);
Page page= (Page)dsm.toObject(new path-to-json-data.json");
页面变量序列化为json:
{
"pageName" : "abc",
"pageImage" : "http://example.com/content.jpg",
"postIds" : [ "123456789012_123456789012" ]
}
DSM非常适合处理复杂的json和xml。