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"
}
]
}
当前回答
A -解释
您可以使用Jackson库，将JSON字符串绑定到POJO(普通旧Java对象)实例中。POJO只是一个只有私有字段和公共getter/setter方法的类。Jackson将遍历这些方法(使用反射)，并将JSON对象映射到POJO实例，因为类的字段名与JSON对象的字段名相匹配。
在JSON对象中，它实际上是一个复合对象，主对象由两个子对象组成。因此，我们的POJO类应该具有相同的层次结构。我将把整个JSON对象称为Page对象。Page对象由PageInfo对象和Post对象数组组成。
所以我们必须创建三个不同的POJO类;
页面类，PageInfo类和Post实例数组的组合 PageInfo类 文章类
我唯一用过的包是Jackson ObjectMapper，我们做的是绑定数据;
com.fasterxml.jackson.databind.ObjectMapper
所需的依赖项，jar文件如下所示;
jackson-core-2.5.1.jar jackson-databind-2.5.1.jar jackson-annotations-2.5.0.jar
这里是所需的代码;
主POJO类:页
package com.levo.jsonex.model;
public class Page {
private PageInfo pageInfo;
private Post[] posts;
public PageInfo getPageInfo() {
return pageInfo;
}
public void setPageInfo(PageInfo pageInfo) {
this.pageInfo = pageInfo;
}
public Post[] getPosts() {
return posts;
}
public void setPosts(Post[] posts) {
this.posts = posts;
}
}
C -儿童POJO类:PageInfo
package com.levo.jsonex.model;
public class PageInfo {
private String pageName;
private String pagePic;
public String getPageName() {
return pageName;
}
public void setPageName(String pageName) {
this.pageName = pageName;
}
public String getPagePic() {
return pagePic;
}
public void setPagePic(String pagePic) {
this.pagePic = pagePic;
}
}
D -儿童POJO类:Post
package com.levo.jsonex.model;
public class Post {
private String post_id;
private String actor_id;
private String picOfPersonWhoPosted;
private String nameOfPersonWhoPosted;
private String message;
private int likesCount;
private String[] comments;
private int timeOfPost;
public String getPost_id() {
return post_id;
}
public void setPost_id(String post_id) {
this.post_id = post_id;
}
public String getActor_id() {
return actor_id;
}
public void setActor_id(String actor_id) {
this.actor_id = actor_id;
}
public String getPicOfPersonWhoPosted() {
return picOfPersonWhoPosted;
}
public void setPicOfPersonWhoPosted(String picOfPersonWhoPosted) {
this.picOfPersonWhoPosted = picOfPersonWhoPosted;
}
public String getNameOfPersonWhoPosted() {
return nameOfPersonWhoPosted;
}
public void setNameOfPersonWhoPosted(String nameOfPersonWhoPosted) {
this.nameOfPersonWhoPosted = nameOfPersonWhoPosted;
}
public String getMessage() {
return message;
}
public void setMessage(String message) {
this.message = message;
}
public int getLikesCount() {
return likesCount;
}
public void setLikesCount(int likesCount) {
this.likesCount = likesCount;
}
public String[] getComments() {
return comments;
}
public void setComments(String[] comments) {
this.comments = comments;
}
public int getTimeOfPost() {
return timeOfPost;
}
public void setTimeOfPost(int timeOfPost) {
this.timeOfPost = timeOfPost;
}
}
E -样本JSON文件:sampleJSONFile.json
我刚刚将JSON示例复制到这个文件中，并将其放在项目文件夹下。
{
"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"
}
]
}
F -演示代码
package com.levo.jsonex;
import java.io.File;
import java.io.IOException;
import java.util.Arrays;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.levo.jsonex.model.Page;
import com.levo.jsonex.model.PageInfo;
import com.levo.jsonex.model.Post;
public class JSONDemo {
public static void main(String[] args) {
ObjectMapper objectMapper = new ObjectMapper();
try {
Page page = objectMapper.readValue(new File("sampleJSONFile.json"), Page.class);
printParsedObject(page);
} catch (IOException e) {
e.printStackTrace();
}
}
private static void printParsedObject(Page page) {
printPageInfo(page.getPageInfo());
System.out.println();
printPosts(page.getPosts());
}
private static void printPageInfo(PageInfo pageInfo) {
System.out.println("Page Info;");
System.out.println("**********");
System.out.println("\tPage Name : " + pageInfo.getPageName());
System.out.println("\tPage Pic : " + pageInfo.getPagePic());
}
private static void printPosts(Post[] posts) {
System.out.println("Page Posts;");
System.out.println("**********");
for(Post post : posts) {
printPost(post);
}
}
private static void printPost(Post post) {
System.out.println("\tPost Id : " + post.getPost_id());
System.out.println("\tActor Id : " + post.getActor_id());
System.out.println("\tPic Of Person Who Posted : " + post.getPicOfPersonWhoPosted());
System.out.println("\tName Of Person Who Posted : " + post.getNameOfPersonWhoPosted());
System.out.println("\tMessage : " + post.getMessage());
System.out.println("\tLikes Count : " + post.getLikesCount());
System.out.println("\tComments : " + Arrays.toString(post.getComments()));
System.out.println("\tTime Of Post : " + post.getTimeOfPost());
}
}
G -演示输出
Page Info;
****(*****
Page Name : abc
Page Pic : http://example.com/content.jpg
Page Posts;
**********
Post Id : 123456789012_123456789012
Actor Id : 1234567890
Pic Of Person Who Posted : http://example.com/photo.jpg
Name Of Person Who Posted : Jane Doe
Message : Sounds cool. Can't wait to see it!
Likes Count : 2
Comments : []
Time Of Post : 1234567890
其他回答
为了便于示例，让我们假设您有一个只有名称的Person类。
private class Person {
public String name;
public Person(String name) {
this.name = name;
}
}
谷歌GSON (Maven)
我个人最喜欢的JSON对象序列化/反序列化。
Gson g = new Gson();
Person person = g.fromJson("{\"name\": \"John\"}", Person.class);
System.out.println(person.name); //John
System.out.println(g.toJson(person)); // {"name":"John"}
更新
如果你想获取单个属性，你可以很容易地使用谷歌库:
JsonObject jsonObject = new JsonParser().parse("{\"name\": \"John\"}").getAsJsonObject();
System.out.println(jsonObject.get("name").getAsString()); //John
Org。JSON (Maven)
如果您不需要对象反序列化，而只是获得一个属性，您可以尝试org。json(或查看上面的GSON示例!)
JSONObject obj = new JSONObject("{\"name\": \"John\"}");
System.out.println(obj.getString("name")); //John
杰克逊(Maven)
ObjectMapper mapper = new ObjectMapper();
Person user = mapper.readValue("{\"name\": \"John\"}", Person.class);
System.out.println(user.name); //John
{
"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"
}
]
}
Java code :
JSONObject obj = new JSONObject(responsejsonobj);
String pageName = obj.getJSONObject("pageInfo").getString("pageName");
JSONArray arr = obj.getJSONArray("posts");
for (int i = 0; i < arr.length(); i++)
{
String post_id = arr.getJSONObject(i).getString("post_id");
......etc
}
我们可以使用JSONObject类将JSON字符串转换为JSON对象， 和遍历JSON对象。使用下面的代码。
JSONObject jObj = new JSONObject(contents.trim());
Iterator<?> keys = jObj.keys();
while( keys.hasNext() ) {
String key = (String)keys.next();
if ( jObj.get(key) instanceof JSONObject ) {
System.out.println(jObj.getString(String key));
}
}
由于还没有人提到它，这里是一个使用Nashorn (Java 8的JavaScript运行时部分，但在Java 11中已弃用)的解决方案的开始。
解决方案
private static final String EXTRACTOR_SCRIPT =
"var fun = function(raw) { " +
"var json = JSON.parse(raw); " +
"return [json.pageInfo.pageName, json.pageInfo.pagePic, json.posts[0].post_id];};";
public void run() throws ScriptException, NoSuchMethodException {
ScriptEngine engine = new ScriptEngineManager().getEngineByName("nashorn");
engine.eval(EXTRACTOR_SCRIPT);
Invocable invocable = (Invocable) engine;
JSObject result = (JSObject) invocable.invokeFunction("fun", JSON);
result.values().forEach(e -> System.out.println(e));
}
性能比较
我编写的JSON内容包含三个数组，分别为20、20和100个元素。我只想从第三个数组中获取100个元素。我使用下面的JavaScript函数来解析和获取我的条目。
var fun = function(raw) {JSON.parse(raw).entries};
使用Nashorn运行一百万次调用需要7.5~7.8秒
(JSObject) invocable.invokeFunction("fun", json);
org。Json需要20~21秒
new JSONObject(JSON).getJSONArray("entries");
杰克逊用时6.5~7秒
mapper.readValue(JSON, Entries.class).getEntries();
在这种情况下，Jackson的性能比Nashorn好，后者的性能比org.json好得多。 Nashorn API比org更难使用。json或Jackson的。根据您的需求，Jackson和Nashorn都是可行的解决方案。
使用minimal-json，它非常快速和容易使用。 你可以从String obj和Stream中解析。
样本数据:
{
"order": 4711,
"items": [
{
"name": "NE555 Timer IC",
"cat-id": "645723",
"quantity": 10,
},
{
"name": "LM358N OpAmp IC",
"cat-id": "764525",
"quantity": 2
}
]
}
解析:
JsonObject object = Json.parse(input).asObject();
int orders = object.get("order").asInt();
JsonArray items = object.get("items").asArray();
创建JSON:
JsonObject user = Json.object().add("name", "Sakib").add("age", 23);
Maven:
<dependency>
<groupId>com.eclipsesource.minimal-json</groupId>
<artifactId>minimal-json</artifactId>
<version>0.9.4</version>
</dependency>
