Java中Jackson库操作json的基本操作

这段工作中总会遇到使用Java处理JSON的情况，大部分都使用的是开源工具Jackson实现的。因此总结一下发上来，希望对看到的人有所帮助。

上一篇文档中，我已经讲过Java如何使用Jackson来对Json进行序列化，这边我再稍微回顾一下。

Jackson中有个ObjectMapper类很是实用，用于Java对象与JSON的互换。
1、Java对象转换为JSON：
User user=new User(); //Java Object
ObjectMapper mapper = new ObjectMapper();
mapper.writeValueAsString(user); //返回字符串
//输出格式化后的字符串(有性能损耗)
mapper.defaultPrettyPrintingWriter().writeValueAsString(user);
mapper.writeValue(new File("c:\\user.json"), user); //指定文件写入
//设置序列化配置(全局),设置序列化时不输出空值.
sharedMapper.getSerializationConfig().setSerializationInclusion(Inclusion.NON_NULL);

2、JSON反序列化为Java对象：
ObjectMapper mapper = new ObjectMapper();
//解析器支持解析单引号
mapper.configure(Feature.ALLOW_SINGLE_QUOTES,true);
//解析器支持解析结束符
mapper.configure(Feature.ALLOW_UNQUOTED_CONTROL_CHARS,true);
HashMap jsonMap = mapper.readValue(json,HashMap.class); //转换为HashMap对象

下面讲解一下Jackson对Json的基本操作：

Map转换为json

package com.pcmall;import java.io.IOException;
import java.util.HashMap;
import java.util.Map;import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;public class Map2Json {/** * Map 转换为 json */ public static void MyTest01()  {  Map<String, String> hashMap = new HashMap<String, String>();  hashMap.put("name", "zhang");  hashMap.put("sex", "1");  hashMap.put("login", "Jack");  hashMap.put("password", "123abc");  try  {  ObjectMapper objectMapper = new ObjectMapper();  String userMapJson = objectMapper.writeValueAsString(hashMap);  JsonNode node = objectMapper.readTree(userMapJson);  // 输出结果转意，输出正确的信息  System.out.println(node.get("password").asText());  // 输出不转意,输出结果会包含""，这是不正确的，除非作为json传递，如果是输出结果值，必须如上一行的操作  System.out.println(node.get("name"));  }  catch (IOException e)  {  }  }  public static void main(String[] args){MyTest01();}
}

输出结果如下：

123abc
"zhang"

解析json格式字符串

package com.pcmall;import java.io.IOException;import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;public class ResolveJson {/** * 解析 json 格式字符串 */  public static void MyTest02()  {  try  {  String str = "{\"data\":{\"birth_day\":7,\"birth_month\":6},\"errcode\":0,\"msg\":\"ok\",\"ret\":0}";  ObjectMapper mapper = new ObjectMapper();  JsonNode root = mapper.readTree(str);  JsonNode data = root.path("data");  JsonNode birth_day = data.path("birth_day");  System.out.println(birth_day.asInt());  JsonNode birth_month = data.path("birth_month");  System.out.println(birth_month.asInt());  JsonNode msg = root.path("msg");  System.out.println(msg.textValue());  }  catch (IOException e)  {  }  }  public static void main(String[] args){MyTest02();}
}

输出结果如下：

7
6
ok

json直接提取值

package com.pcmall;import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;public class GetPartJson {/** * json 直接提取 值 */  public static void MyTest03()  {  try  {  // 演示字符串  String str = "{\"data\":{\"hasnext\":0,\"info\":[{\"id\":\"288206077664983\",\"timestamp\":1371052476},{\"id\":\"186983078111768\",\"timestamp\":1370944068},{\"id\":\"297031120529307\",\"timestamp\":1370751789},{\"id\":\"273831022294863\",\"timestamp\":1369994812}],\"timestamp\":1374562897,\"totalnum\":422},\"errcode\":0,\"msg\":\"ok\",\"ret\":0,\"seqid\":5903702688915195270}";  ObjectMapper mapper = new ObjectMapper();  JsonNode root = mapper.readTree(str);  // 提取 data  JsonNode data = root.path("data");  // 提取 info  JsonNode info = data.path("info");  System.out.println(info.size());  // 得到 info 的第 0 个  JsonNode item = info.get(0);  System.out.println(item.get("id"));  System.out.println(item.get("timestamp"));  // 得到 info 的第 2 个  item = info.get(2);  System.out.println(item.get("id"));  System.out.println(item.get("timestamp"));  // 遍历 info 内的 array  if (info.isArray())  {  for (JsonNode objNode : info)  {  System.out.println(objNode);  }  }  }  catch (Exception e)  {  }  }  public static void main(String[] args){MyTest03();}
}

输出结果如下：

4
"288206077664983"
1371052476
"297031120529307"
1370751789
{"id":"288206077664983","timestamp":1371052476}
{"id":"186983078111768","timestamp":1370944068}
{"id":"297031120529307","timestamp":1370751789}
{"id":"273831022294863","timestamp":1369994812}

创建一个Json，并向该json添加内容

package com.pcmall;import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ArrayNode;
import com.fasterxml.jackson.databind.node.ObjectNode;public class CreateJson {/** * 创建一个 json，并向该 json 添加内容 */  public static void MyTest04()  {  try  {  ObjectMapper mapper = new ObjectMapper();  ObjectNode root1 = mapper.createObjectNode();  root1.put("nodekey1", 1);  root1.put("nodekey2", 2);  System.out.println(root1.toString());  //Create the root node  ObjectNode root = mapper.createObjectNode ();  //Create a child node  ObjectNode node1 = mapper.createObjectNode ();  node1.put ("nodekey1", 1);  node1.put ("nodekey2", 2);  //Bind the child nodes  root.put ("child", node1);  //Array of nodes  ArrayNode arrayNode = mapper.createArrayNode ();  arrayNode.add (node1);  arrayNode.add (1);  //Bind array node  root.put ("arraynode", arrayNode);  System.out.println (mapper.writeValueAsString (root));  // 得到的输出信息  // {"child":{"nodekey1":1,"nodekey2":2},"arraynode":[{"nodekey1":1,"nodekey2":2},1]}  }  catch (Exception e)  {  }  }  public static void main(String[] args){MyTest04();}
}

输出结果如下：

{"nodekey1":1,"nodekey2":2}
{"child":{"nodekey1":1,"nodekey2":2},"arraynode":[{"nodekey1":1,"nodekey2":2},1]}

创建一个array node

package com.pcmall;import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ArrayNode;
import com.fasterxml.jackson.databind.node.ObjectNode;public class CreateNodeArray {// 创建一个 array node  public static void MyTest05()  {  try  {  ObjectMapper mapper = new ObjectMapper();  ArrayNode arrayNode = mapper.createArrayNode();  int i = 0;  // 在 array 内创建 3 组 node 存入 array  for (i = 0; i < 3; i++)  {  // 创建一个 node  ObjectNode node = mapper.createObjectNode();  node.put("nodeA", i);  node.put("nodeB", i);  node.put("nodeC", i);  // 向 array 内添 node  arrayNode.add(node);  }  // 根  ObjectNode root = mapper.createObjectNode();  root.put("total", i);  root.put("rows", arrayNode);  System.out.println(mapper.writeValueAsString(root));  // 得到的输出信息  // {"total":3,"rows":[{"nodeA":0,"nodeB":0,"nodeC":0},{"nodeA":1,"nodeB":1,"nodeC":1},{"nodeA":2,"nodeB":2,"nodeC":2}]}  }  catch (Exception e)  {  e.printStackTrace();  }  }  public static void main(String[] args){MyTest05();}
}

输出结果如下：

{"total":3,"rows":[{"nodeA":0,"nodeB":0,"nodeC":0},{"nodeA":1,"nodeB":1,"nodeC":1},{"nodeA":2,"nodeB":2,"nodeC":2}]}

在添加 array 节点时，put node 的方法已经过时，将使用 set 方法添加 array 节点，举例：
root.set ("rows", arrayNode);

实际工作中应用

使用Firefox的RESTClient插件进行测试，输入URL，输出如下图所示的结果。

其中基础类如下：

import java.util.Date;public class SaleOrderItem {private String spxx01;private String spxx04;private float lsdi05;private Date lsdi11;private long lsd01;private long lsdi01;private float lsdi02;private String gsxx01;public String getSpxx01() {return spxx01;}public void setSpxx01(String spxx01) {this.spxx01 = spxx01;}public String getSpxx04() {return spxx04;}public void setSpxx04(String spxx04) {this.spxx04 = spxx04;}public float getLsdi05() {return lsdi05;}public void setLsdi05(float lsdi05) {this.lsdi05 = lsdi05;}public Date getLsdi11() {return lsdi11;}public void setLsdi11(Date lsdi11) {this.lsdi11 = lsdi11;}public long getLsd01() {return lsd01;}public void setLsd01(long lsd01) {this.lsd01 = lsd01;}public long getLsdi01() {return lsdi01;}public void setLsdi01(long lsdi01) {this.lsdi01 = lsdi01;}public float getLsdi02() {return lsdi02;}public void setLsdi02(float lsdi02) {this.lsdi02 = lsdi02;}public String getGsxx01() {return gsxx01;}public void setGsxx01(String gsxx01) {this.gsxx01 = gsxx01;}@Overridepublic String toString(){return  spxx04; }
}

业务类使用Spring RestTemplate解析RESTful服务获取到Json，然后调用ObjectMapper对象mapper的readValue(String,TypeReference)方法获取到SaleOrderItem列表。

代码如下：

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;import org.springframework.web.client.RestClientException;
import org.springframework.web.client.RestTemplate;import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;public class RestWebservice {/** * @param args * @throws IOException * @throws JsonProcessingException * @throws Exception * @throws RestClientException */ public static void main(String[] args) throws JsonProcessingException, IOException{ RestTemplate restTemplate = new RestTemplate();   //get方式*********************************************************************************************************** //参数直接放在URL中 String message = restTemplate.getForObject("http://xxx.xxx.xxx.xxx:8080/pad/interface/poslsd/saleOrderDetail?saleOrder=5078603&gsxx=0001", String.class ); System.out.println(message); List<SaleOrderItem> saleOrderItems = new ArrayList<SaleOrderItem>();ObjectMapper mapper = new ObjectMapper();JsonNode root = mapper.readTree(message);JsonNode data = root.path("data");String strData = data.toString();if(data.isArray()){saleOrderItems = mapper.readValue(strData, new TypeReference<List<SaleOrderItem>>(){});System.out.println(saleOrderItems.size());for(SaleOrderItem item : saleOrderItems){System.out.println(item);}}} 
}

输出结果如下：

{"code":10001,"message":"操作成功","total":1,"data":[{"spxx01":97321,"spxx04":"同方商用主机超越Z400","lsdi05":1.0,"lsdi11":1460044800000,"lsd01":5078603,"lsdi01":507860301,"lsdi02":2999.0,"gsxx01":"0001"}]}
1
同方商用主机超越Z400