JackSon fasterxml学习

概述

Jackson框架是基于Java平台的一套数据处理工具，被称为“最好的Java Json解析器”。 
Jackson框架包含了3个核心库：streaming,databind,annotations.Jackson还包含了其它数据处理类库，此外不作说明。
Jackson版本： 1.x (目前版本从1.1~1.9)与2.x。1.x与2.x从包的命名上可以看出来，1.x的类库中，包命名以：org.codehaus.jackson.xxx开头，而2.x类库中包命令：com.fastxml.jackson.xxx开头

Jackson Home Page：https://github.com/FasterXML/jackson
Jackson Wiki：http://wiki.fasterxml.com/JacksonHome
Jackson doc: https://github.com/FasterXML/jackson-docs
Jackson Download Page：http://wiki.fasterxml.com/JacksonDownload

准备工作

本文所有程序都基于JDK1.7,依赖jackon的三个核心类库：
jackson-core-2.5.3.jar
jackson-annotations-2.5.3.jar
jackson-databind-2.5.3.jar

Jackson处理Json

Jackson提供了三种可选的Json处理方法：流式API(Streaming API) 、树模型(Tree Model)、数据绑定(Data Binding)。从使用角度来看，比较一下这三种处理Json的方式的特性：

Streaming API：是效率最高的处理方式(开销低、读写速度快，但程序编写复杂度高)
Tree Model：是最灵活的处理方式
Data Binding：是最常用的处理方式

下面我们通过例子程序分别使用DataBinding,TreeModel,Streaming的方式来创建和解析Json字符串

1.DataBinding处理Json

Jackson支持Java对象与Json之间的相互转化。java对象序列化为json字符串，json字符串也可以反序列化为相同的java对象。

(1)java对象转化成json:

Province.java

package com.jackson.json.databinding;

public class Province {
    public String name;
    public int population;
    public String[] city;
}

package com.jackson.json.databinding;
public class Province {

public String name;

public int population;

public String[] city;

}

Country.java

package com.jackson.json.databinding;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Country {
    // 注意：被序列化的bean的private属性字段需要创建getter方法或者属性字段应该为public
    private String country_id;
    private Date birthDate;
    private List<String> nation = new ArrayList<String>();
    private String[] lakes;
    private List<Province> provinces = new ArrayList<Province>();
    private Map<String, Integer> traffic = new HashMap<String, Integer>();

    public Country() {
        // TODO Auto-generated constructor stub
    }

    public Country(String countryId) {
        this.country_id = countryId;
    }

    public String getCountry_id() {
        return country_id;
    }

    public void setCountry_id(String country_id) {
        this.country_id = country_id;
    }

    public Date getBirthDate() {
        return birthDate;
    }

    public void setBirthDate(Date birthDate) {
        this.birthDate = birthDate;
    }

    public List<String> getNation() {
        return nation;
    }

    public void setNation(List<String> nation) {
        this.nation = nation;
    }

    public String[] getLakes() {
        return lakes;
    }

    public void setLakes(String[] lakes) {
        this.lakes = lakes;
    }

    public Integer get(String key) {
        return traffic.get(key);
    }

    public Map<String, Integer> getTraffic() {
        return traffic;
    }

    public void setTraffic(Map<String, Integer> traffic) {
        this.traffic = traffic;
    }

    public void addTraffic(String key, Integer value) {
        traffic.put(key, value);
    }

    public List<Province> getProvinces() {
        return provinces;
    }

    public void setProvinces(List<Province> provinces) {
        this.provinces = provinces;
    }

    @Override
    public String toString() {
        return “Country [country_id=” + country_id + “, birthDate=” + birthDate
                + ”, nation=” + nation + “, lakes=” + Arrays.toString(lakes)
                + ”, province=” + provinces + “, traffic=” + traffic + “]”;
    }

}

package com.jackson.json.databinding;
import java.util.ArrayList;

import java.util.Arrays;

import java.util.Date;

import java.util.HashMap;

import java.util.List;

import java.util.Map;
public class Country {

// 注意：被序列化的bean的private属性字段需要创建getter方法或者属性字段应该为public

private String country_id;

private Date birthDate;

private List<String> nation = new ArrayList<String>();

private String[] lakes;

private List<Province> provinces = new ArrayList<Province>();

private Map<String, Integer> traffic = new HashMap<String, Integer>();
public Country() {
    // TODO Auto-generated constructor stub
}

public Country(String countryId) {
    this.country_id = countryId;
}

public String getCountry_id() {
    return country_id;
}

public void setCountry_id(String country_id) {
    this.country_id = country_id;
}

public Date getBirthDate() {
    return birthDate;
}

public void setBirthDate(Date birthDate) {
    this.birthDate = birthDate;
}

public List&lt;String&gt; getNation() {
    return nation;
}

public void setNation(List&lt;String&gt; nation) {
    this.nation = nation;
}

public String[] getLakes() {
    return lakes;
}

public void setLakes(String[] lakes) {
    this.lakes = lakes;
}

public Integer get(String key) {
    return traffic.get(key);
}

public Map&lt;String, Integer&gt; getTraffic() {
    return traffic;
}

public void setTraffic(Map&lt;String, Integer&gt; traffic) {
    this.traffic = traffic;
}

public void addTraffic(String key, Integer value) {
    traffic.put(key, value);
}

public List&lt;Province&gt; getProvinces() {
    return provinces;
}

public void setProvinces(List&lt;Province&gt; provinces) {
    this.provinces = provinces;
}

@Override
public String toString() {
    return "Country [country_id=" + country_id + ", birthDate=" + birthDate
            + ", nation=" + nation + ", lakes=" + Arrays.toString(lakes)
            + ", province=" + provinces + ", traffic=" + traffic + "]";
}

}

JavaBeanSerializeToJson.java

package com.jackson.json.databinding;

import java.io.File;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.List;

import com.fasterxml.jackson.annotation.JsonInclude.Include;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

public class JavaBeanSerializeToJson {

    public static void convert() throws Exception {
        // 使用ObjectMapper来转化对象为Json
        ObjectMapper mapper = new ObjectMapper();
        // 添加功能，让时间格式更具有可读性
        SimpleDateFormat dateFormat = new SimpleDateFormat(“yyyy-MM-dd”);
        mapper.setDateFormat(dateFormat);

        Country country = new Country(“China”);
        country.setBirthDate(dateFormat.parse(”1949-10-01”));
        country.setLakes(new String[] { “Qinghai Lake”, “Poyang Lake”,
                ”Dongting Lake”, “Taihu Lake” });

        List<String> nation = new ArrayList<String>();
        nation.add(”Han”);
        nation.add(”Meng”);
        nation.add(”Hui”);
        nation.add(”WeiWuEr”);
        nation.add(”Zang”);
        country.setNation(nation);

        Province province = new Province();
        province.name = ”Shanxi”;
        province.population = 37751200;
        Province province2 = new Province();
        province2.name = ”ZheJiang”;
        province2.population = 55080000;
        List<Province> provinces = new ArrayList<Province>();
        provinces.add(province);
        provinces.add(province2);
        country.setProvinces(provinces);

        country.addTraffic(”Train(KM)”, 112000);
        country.addTraffic(”HighWay(KM)”, 4240000);
        // 为了使JSON视觉上的可读性，增加一行如下代码，注意，在生产中不需要这样，因为这样会增大Json的内容
        mapper.configure(SerializationFeature.INDENT_OUTPUT, true);
        // 配置mapper忽略空属性
        mapper.setSerializationInclusion(Include.NON_EMPTY);
        // 默认情况，Jackson使用Java属性字段名称作为 Json的属性名称,也可以使用Jackson annotations(注解)改变Json属性名称
        mapper.writeValue(new File(“country.json”), country);
    }

    public static void main(String[] args) throws Exception {
        convert();
    }

}

package com.jackson.json.databinding;
import java.io.File;

import java.text.SimpleDateFormat;

import java.util.ArrayList;

import java.util.List;
import com.fasterxml.jackson.annotation.JsonInclude.Include;

import com.fasterxml.jackson.databind.ObjectMapper;

import com.fasterxml.jackson.databind.SerializationFeature;
public class JavaBeanSerializeToJson {
public static void convert() throws Exception {
    // 使用ObjectMapper来转化对象为Json
    ObjectMapper mapper = new ObjectMapper();
    // 添加功能，让时间格式更具有可读性
    SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
    mapper.setDateFormat(dateFormat);

    Country country = new Country("China");
    country.setBirthDate(dateFormat.parse("1949-10-01"));
    country.setLakes(new String[] { "Qinghai Lake", "Poyang Lake",
            "Dongting Lake", "Taihu Lake" });

    List<String> nation = new ArrayList<String>();
    nation.add("Han");
    nation.add("Meng");
    nation.add("Hui");
    nation.add("WeiWuEr");
    nation.add("Zang");
    country.setNation(nation);

    Province province = new Province();
    province.name = "Shanxi";
    province.population = 37751200;
    Province province2 = new Province();
    province2.name = "ZheJiang";
    province2.population = 55080000;
    List<Province> provinces = new ArrayList<Province>();
    provinces.add(province);
    provinces.add(province2);
    country.setProvinces(provinces);

    country.addTraffic("Train(KM)", 112000);
    country.addTraffic("HighWay(KM)", 4240000);
    // 为了使JSON视觉上的可读性，增加一行如下代码，注意，在生产中不需要这样，因为这样会增大Json的内容
    mapper.configure(SerializationFeature.INDENT_OUTPUT, true);
    // 配置mapper忽略空属性
    mapper.setSerializationInclusion(Include.NON_EMPTY);
    // 默认情况，Jackson使用Java属性字段名称作为 Json的属性名称,也可以使用Jackson annotations(注解)改变Json属性名称
    mapper.writeValue(new File("country.json"), country);
}

public static void main(String[] args) throws Exception {
    convert();
}

}

程序运行后生成country.json，内容如下：

{
  “country_id” : “China”,
  “birthDate” : “1949-10-01”,
  “nation” : [ “Han”, “Meng”, “Hui”, “WeiWuEr”, “Zang” ],
  “lakes” : [ “Qinghai Lake”, “Poyang Lake”, “Dongting Lake”, “Taihu Lake” ],
  “provinces” : [ {
    “name” : “Shanxi”,
    “population” : 37751200
  }, {
    “name” : “ZheJiang”,
    “population” : 55080000
  } ],
  “traffic” : {
    “HighWay(KM)” : 4240000,
    “Train(KM)” : 112000
  }
}

{
  "country_id" : "China",
  "birthDate" : "1949-10-01",
  "nation" : [ "Han", "Meng", "Hui", "WeiWuEr", "Zang" ],
  "lakes" : [ "Qinghai Lake", "Poyang Lake", "Dongting Lake", "Taihu Lake" ],
  "provinces" : [ {
    "name" : "Shanxi",
    "population" : 37751200
  }, {
    "name" : "ZheJiang",
    "population" : 55080000
  } ],
  "traffic" : {
    "HighWay(KM)" : 4240000,
    "Train(KM)" : 112000
  }
}

(2)Json字符串反序列化为java对象：

package com.jackson.json.databinding;

import java.io.File;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Iterator;
import java.util.List;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

/**
 * 将Json字符串反序列化为Java对象
 */
public class JsonDeserializeToJava {

    public static void main(String[] args) throws Exception {
        //ObjectMapper类用序列化与反序列化映射器
        ObjectMapper mapper = new ObjectMapper();
        File json = new File(“country.json”);
        //当反序列化json时，未知属性会引起的反序列化被打断，这里我们禁用未知属性打断反序列化功能，
        //因为，例如json里有10个属性，而我们的bean中只定义了2个属性，其它8个属性将被忽略
        mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);

        //从json映射到java对象，得到country对象后就可以遍历查找,下面遍历部分内容，能说明问题就可以了
        Country country = mapper.readValue(json, Country.class);
        System.out.println(”country_id:”+country.getCountry_id());
        //设置时间格式，便于阅读
        SimpleDateFormat dateformat = new SimpleDateFormat(“yyyy-MM-dd”);
        String birthDate = dateformat.format(country.getBirthDate());
        System.out.println(”birthDate:”+birthDate);

        List<Province> provinces = country.getProvinces();
        for (Province province : provinces) {
            System.out.println(”province:”+province.name + “
” + “population:”+province.population);
        }
    }
}

package com.jackson.json.databinding;
import java.io.File;

import java.io.IOException;

import java.text.SimpleDateFormat;

import java.util.Iterator;

import java.util.List;
import com.fasterxml.jackson.core.JsonParseException;

import com.fasterxml.jackson.databind.DeserializationFeature;

import com.fasterxml.jackson.databind.JsonMappingException;

import com.fasterxml.jackson.databind.ObjectMapper;
/**


将Json字符串反序列化为Java对象

*/

public class JsonDeserializeToJava {
public static void main(String[] args) throws Exception {

//ObjectMapper类用序列化与反序列化映射器

ObjectMapper mapper = new ObjectMapper();

File json = new File("country.json");

//当反序列化json时，未知属性会引起的反序列化被打断，这里我们禁用未知属性打断反序列化功能，

//因为，例如json里有10个属性，而我们的bean中只定义了2个属性，其它8个属性将被忽略

mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
 //从json映射到java对象，得到country对象后就可以遍历查找,下面遍历部分内容，能说明问题就可以了
 Country country = mapper.readValue(json, Country.class);
 System.out.println("country_id:"+country.getCountry_id());
 //设置时间格式，便于阅读
 SimpleDateFormat dateformat = new SimpleDateFormat("yyyy-MM-dd");
 String birthDate = dateformat.format(country.getBirthDate());
 System.out.println("birthDate:"+birthDate);

 List<Province> provinces = country.getProvinces();
 for (Province province : provinces) {
     System.out.println("province:"+province.name + "
" + "population:"+province.population);
 }

}

}