jackson包提供了java对象与json相互转换的API。java
Jackson要求java对象是一个POJO对象,即它是一个普通JavaBean对象。此外,若是字段是用private修饰的,则必须有getXXX()方法,不然字段用public修饰。json
json常见格式以下数组
{ "key1" : value, "key2" : [...], "key3" : {...} }
jackson把JavaBean对象的每一个字段映射为json的键,json键值由JavaBean的getXXX()方法肯定。app
json键值从形式上看,能够分为基本类型(字符串、数值)、数组、字典。当JavaBean的字段声明为基本类型时对应json的基本类型,当JavaBean声明为数组或链表时对应json的数组类型,当JavaBean声明为字典或对象时对应json的字典类型。this
定义一个符合JavaBean规则的类code
package com.weixia.Json; import java.util.ArrayList; import java.util.HashMap; import java.util.Map; public class Bean { private String name; private int[] stature; private Friend friend; private ArrayList<String> song; private Map<String,Integer> score = new HashMap<String,Integer>(); public Bean(String name) { this.name = name; } public String getName() { return this.name; } public void setStature(int[] stature) { this.stature = stature; } public int[] getStature() { return this.stature; } public void setSong(ArrayList<String> song) { this.song = song; } public ArrayList<String> getSong() { return this.song; } public void setFriend(Friend friend) { this.friend = friend; } public Friend getFriend() { return this.friend; } public void addScore(String subject,Integer score) { this.score.put(subject, score); } public Map getScore() { return this.score; } } class Friend { public String name; public int age; }
将Bean对象序列化为json以下xml
package com.weixia.Json; import java.util.ArrayList; import com.fasterxml.jackson.databind.ObjectMapper; import com.fasterxml.jackson.databind.SerializationFeature; import com.fasterxml.jackson.annotation.JsonInclude.Include; public class App { public static void main( String[] args ) throws Exception { Bean bean = new Bean("Album"); ObjectMapper mapper = new ObjectMapper(); bean.setStature(new int[] {88,60,89}); ArrayList<String> song = new ArrayList<String>(); song.add("奇异恩典"); song.add("东京的都"); bean.setSong(song); Friend friend = new Friend(); friend.name = "小明"; friend.age = 24; bean.setFriend(friend); bean.addScore("Math", 100); bean.addScore("PE", 88); mapper.configure(SerializationFeature.INDENT_OUTPUT, true); //格式化输出 mapper.configure(SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS, true); //键按天然顺序输出 mapper.setSerializationInclusion(Include.NON_EMPTY); //忽略POJO中属性为空的字段 mapper.writeValue(System.out, bean); } }
json文件以下:对象
{ "name": "weixia", "age": 24, "stature":[89,66,89], "friend":{ "name":"zhiye", "age":24 }, "test":"" }
定义一个符合JaveBean规则的类字符串
package com.weixia.Json; public class People { private String name; private int age; private Friend friend; private int[] stature; public String getName() { return this.name; } public int getAge() { return this.age; } public Friend getFriend() { return this.friend; } public int[] getStature() { return this.stature; } } class Friend { public String name; public int age; }
将json反序列化为java对象get
package com.weixia.Json; import java.io.File; import com.fasterxml.jackson.databind.DeserializationFeature; import com.fasterxml.jackson.databind.ObjectMapper; public class Json2Bean { public static void main(String[] args) throws Exception { ObjectMapper mapper = new ObjectMapper(); mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false); //忽略未知的属性 People people = mapper.readValue(new File("F:\\test.json"), People.class); System.out.println(people.getName()); System.out.println(people.getAge()); System.out.println(people.getFriend()); int[] stature = people.getStature(); for (int num : stature) { System.out.println(num); } } }