Java操作JSON数据(4,end)--Jackson操作JSON数据

jackson是springboot默认使用的json处理库，它可以轻松的将java对象转换成json对象，同样也可以将json转换成java对象。本文介绍下jackson的基本使用方法，包括序列化和反序列化；文中所使用到的软件版本：java 1.8.0_191、jackson 2.10.0。

1、引入依赖

<dependency>
  <groupid>com.fasterxml.jackson.core</groupid>
  <artifactid>jackson-core</artifactid>
  <version>2.10.0</version>
</dependency>
<dependency>
  <groupid>com.fasterxml.jackson.core</groupid>
  <artifactid>jackson-databind</artifactid>
  <version>2.10.0</version>
</dependency>
<dependency>
  <groupid>com.fasterxml.jackson.core</groupid>
  <artifactid>jackson-annotations</artifactid>
  <version>2.10.0</version>
</dependency>

如果使用的是springboot，默认就使用了jackson，则无需引入。

2、序列化

    public static string serialize() {
        mybean bean = new mybean();
        bean.sets("测试字符串");
        calendar calendar = calendar.getinstance();
        calendar.add(calendar.hour_of_day, -1);
        bean.setd(calendar.gettime());

        list<mybean> list = new arraylist<mybean>();
        list.add(bean);
        map<string, list<mybean>> map = new hashmap<string, list<mybean>>();
        map.put("data", list);
        string result = "";
        try {
            objectmapper objectmapper = new objectmapper();
            //设置日期格式，也可在类属性上使用@jsonformat(pattern="yyyy-mm-dd hh:mm:ss")来设置
            objectmapper.setdateformat(new simpledateformat("yyyy-mm-dd hh:mm:ss"));
            objectmapper.setserializationinclusion(include.always);
            //字符串如果为null则输出""
            objectmapper.setserializerfactory(objectmapper.getserializerfactory().withserializermodifier(new beanserializermodifier() {
                @override
                public list<beanpropertywriter> changeproperties(serializationconfig config, beandescription beandesc, list<beanpropertywriter> beanproperties) {
                    for (beanpropertywriter writer : beanproperties) {
                        class<?> clazz = writer.gettype().getrawclass();
                        if (charsequence.class.isassignablefrom(clazz) || character.class.isassignablefrom(clazz)) {
                            writer.assignnullserializer(new jsonserializer<object>() {
                                @override
                                public void serialize(object o, jsongenerator jsongenerator, serializerprovider serializerprovider) throws ioexception {
                                    jsongenerator.writestring("");
                                }
                            });
                        }
                    }
                    return beanproperties;
                }
            }));

            result = objectmapper.writevalueasstring(map);
            system.out.println(result);
        } catch (exception e) {
            e.printstacktrace();
        }

        return result;
    }

3、反序列化

    public static void deserialize() {
        string s = serialize();
        try {
            objectmapper objectmapper = new objectmapper();
            objectmapper.setdateformat(new simpledateformat("yyyy-mm-dd hh:mm:ss"));
            typereference<map<string, list<mybean>>> type = new typereference<map<string, list<mybean>>>(){};
            map<string, list<mybean>> map = objectmapper.readvalue(s, type);
            system.out.println(map);
            
            //树模型api
            jsonnode root = objectmapper.readtree(s);
            jsonnode bean = root.get("data").get(0);
            system.out.println(bean.get("s").astext());
            //...
        } catch (exception e) {
            e.printstacktrace();
        }
    }

4、完整例子

package com.inspur.demo.json;

import java.io.ioexception;
import java.text.simpledateformat;
import java.util.arraylist;
import java.util.calendar;
import java.util.hashmap;
import java.util.list;
import java.util.map;

import com.fasterxml.jackson.annotation.jsoninclude.include;
import com.fasterxml.jackson.core.jsongenerator;
import com.fasterxml.jackson.core.type.typereference;
import com.fasterxml.jackson.databind.beandescription;
import com.fasterxml.jackson.databind.jsonnode;
import com.fasterxml.jackson.databind.jsonserializer;
import com.fasterxml.jackson.databind.objectmapper;
import com.fasterxml.jackson.databind.serializationconfig;
import com.fasterxml.jackson.databind.serializerprovider;
import com.fasterxml.jackson.databind.ser.beanpropertywriter;
import com.fasterxml.jackson.databind.ser.beanserializermodifier;

/**
 * jackson操作json数据
 */
public class jacksoncase {
    /**
     * 序列化
     */
    public static string serialize() {
        mybean bean = new mybean();
        bean.sets("测试字符串");
        calendar calendar = calendar.getinstance();
        calendar.add(calendar.hour_of_day, -1);
        bean.setd(calendar.gettime());

        list<mybean> list = new arraylist<mybean>();
        list.add(bean);
        map<string, list<mybean>> map = new hashmap<string, list<mybean>>();
        map.put("data", list);
        string result = "";
        try {
            objectmapper objectmapper = new objectmapper();
            //设置日期格式，也可在类属性上使用@jsonformat(pattern="yyyy-mm-dd hh:mm:ss")来设置
            objectmapper.setdateformat(new simpledateformat("yyyy-mm-dd hh:mm:ss"));
            objectmapper.setserializationinclusion(include.always);
            //字符串如果为null则输出""
            objectmapper.setserializerfactory(objectmapper.getserializerfactory().withserializermodifier(new beanserializermodifier() {
                @override
                public list<beanpropertywriter> changeproperties(serializationconfig config, beandescription beandesc, list<beanpropertywriter> beanproperties) {
                    for (beanpropertywriter writer : beanproperties) {
                        class<?> clazz = writer.gettype().getrawclass();
                        if (charsequence.class.isassignablefrom(clazz) || character.class.isassignablefrom(clazz)) {
                            writer.assignnullserializer(new jsonserializer<object>() {
                                @override
                                public void serialize(object o, jsongenerator jsongenerator, serializerprovider serializerprovider) throws ioexception {
                                    jsongenerator.writestring("");
                                }
                            });
                        }
                    }
                    return beanproperties;
                }
            }));

            result = objectmapper.writevalueasstring(map);
            system.out.println(result);
        } catch (exception e) {
            e.printstacktrace();
        }

        return result;
    }

    /**
     * 反序列化
     */
    public static void deserialize() {
        string s = serialize();
        try {
            objectmapper objectmapper = new objectmapper();
            objectmapper.setdateformat(new simpledateformat("yyyy-mm-dd hh:mm:ss"));
            typereference<map<string, list<mybean>>> type = new typereference<map<string, list<mybean>>>(){};
            map<string, list<mybean>> map = objectmapper.readvalue(s, type);
            system.out.println(map);
            
            //树模型api
            jsonnode root = objectmapper.readtree(s);
            jsonnode bean = root.get("data").get(0);
            system.out.println(bean.get("s").astext());
            //...
        } catch (exception e) {
            e.printstacktrace();
        }
    }
    
    public static void main(string[] args) {
        serialize();
        deserialize();
    }

}

package com.inspur.demo.json;

import java.util.arrays;
import java.util.date;

public class mybean {
    private string s = "字符串";
    private string s2;
    private string s3 = "字符串3";
    private int i = 123;
    private integer i2;
    private char c = '到';
    private char[] c2 = new char[]{'a', 'b'};
    private date d = new date();
    private date[] d2 = new date[]{new date(), new date()};
    public string gets() {
        return s;
    }
    public void sets(string s) {
        this.s = s;
    }
    public string gets2() {
        return s2;
    }
    public void sets2(string s2) {
        this.s2 = s2;
    }
    public string gets3() {
        return s3;
    }
    public void sets3(string s3) {
        this.s3 = s3;
    }
    public int geti() {
        return i;
    }
    public void seti(int i) {
        this.i = i;
    }
    public integer geti2() {
        return i2;
    }
    public void seti2(integer i2) {
        this.i2 = i2;
    }
    public char getc() {
        return c;
    }
    public void setc(char c) {
        this.c = c;
    }
    public char[] getc2() {
        return c2;
    }
    public void setc2(char[] c2) {
        this.c2 = c2;
    }
    public date getd() {
        return d;
    }
    public void setd(date d) {
        this.d = d;
    }
    public date[] getd2() {
        return d2;
    }
    public void setd2(date[] d2) {
        this.d2 = d2;
    }
    @override
    public string tostring() {
        return "mybean [s=" + s + ", s2=" + s2 + ", s3=" + s3 + ", i=" + i + ", i2=" + i2 + ", c=" + c + ", c2="
                + arrays.tostring(c2) + ", d=" + d + ", d2=" + arrays.tostring(d2) + "]";
    }
}