java Jackson 库操作 json 的基本演示

核心库下载地址

http://repo1.maven.org/maven2/com/fasterxml/jackson/core/

jackson-annotations-2.2.2.jar

jackson-core-2.2.2.jar

jackson-databind-2.2.2.jar

 

文件类型支持模块

http://repo1.maven.org/maven2/com/fasterxml/jackson/dataformat/

jackson-dataformat-xml-2.2.2.jar

 

导入库

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.node.ObjectNode;
import com.fasterxml.jackson.databind.node.ArrayNode;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonEncoding;
import com.fasterxml.jackson.core.JsonParseException;

 

  /**
   * Map 转换为 json
   */
  public static void MyTest01()
  {
    Map hashMap = new HashMap();
    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)
    {
    }
  }

 

/**
   * 解析 json 格式字符串
   */
  public static void MyTest03()
  {
    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)
    {
    }
  }

 

/**
   * json 直接提取 值
   */
  public static void MyTest05()
  {
    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)
    {

    }
  }

 

  /**
   * 创建一个 json，并向该 json 添加内容
   */
  public static void MyTest07()
  {
    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)
    {

    }
  }

 

  // 创建一个 array node
  public static void MyTest07()
  {
    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();
    }
  }

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);

 

将 java object 转化为 json string，被转换的对象类似 YourObject 这样，利用 ObjectWrite 进行转换。

 

public YourObject
{
  private str = "";
  public void setStr(String str)
  {
    this.str = str;
  }
  public String getStr()
  {
    return str;
  }
}

 

    // 将 java 对象 转换为 json string
    ObjectWriter objectWriter = new ObjectMapper().writer().withDefaultPrettyPrinter();
    String json = null;
    try
    {
      json = objectWriter.writeValueAsString(yourObject);
    }
    catch (JsonProcessingException e)
    {
      e.printStackTrace();
    }

 

XML 转换为 JSON 也可以利用 Jackson 完成

 

  /**
   * 将 XML 转换为 JSON
   * @param args
   */
  public void XML2JSON()
  {
    String xml = "id1val1"
        + "id2val2"
        + "id3val3";
    try
    {
      XmlMapper xmlMapper = new XmlMapper();
      Map entries = xmlMapper.readValue(xml, Map.class);
      ObjectMapper jsonMapper = new ObjectMapper();
      String json = jsonMapper.writeValueAsString(entries);
      System.out.println(json);
    }
    catch (JsonParseException e)
    {
      e.printStackTrace();
    }
    catch (JsonMappingException e)
    {
      e.printStackTrace();
    }
    catch (JsonProcessingException e)
    {
      e.printStackTrace();
    }
    catch (IOException e)
    {
      e.printStackTrace();
    }
  }

 

 

 

 

 

JsonNode 字符串类型：textValue 有效, asText 有效，toString 获取的结果带引号
JsonNode 数值类型：textValue 获得的是 null， asText 有效, toString 有效，各输出方式比较如下，附代码：

 

原始信息	toString()	asText()	textValue()	numberType()
123	123	123	null	INT
123.456	123.456	123.456	null	DOUBLE
"123.45600"	"123.45600"	123.456	123.456	null
""	""			null
"0"	"0"	0	0	null
"null"	"null"	null	null	null
null	null	null	null	null

 

 

package other;

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.node.ObjectNode;
import com.fasterxml.jackson.databind.node.ArrayNode;
import com.fasterxml.jackson.core.JsonGenerator;

import java.io.IOException;

import com.fasterxml.jackson.core.JsonEncoding;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.JsonParser.NumberType;
import com.fasterxml.jackson.core.JsonProcessingException;

public class Jackson1
{

  public static void main(String[] args)
  {
    String str = "{\"data\":{\"number1\":123,\"number2\":123.45600,\"number3\":\"123.45600\""
        + ",\"number4\":\"\",\"number5\":\"0\",\"number6\":\"null\",\"number7\":null}}";

    try
    {
      ObjectMapper mapper = new ObjectMapper();
      JsonNode root = mapper.readTree(str);

      JsonNode data = root.path("data");

      for (int i = 1; i <= 7; i++)
      {
        String strNodeName = "number" + String.valueOf(i);

        if (data.has(strNodeName) == true)
        {
          System.out.println(String.format("原始节点信息 %s", data.get(strNodeName)));

          String str1 = data.get(strNodeName).toString();
          System.out.println(String.format("toString() 输出: %s", str1));

          String str2 = data.get(strNodeName).asText();
          System.out.println(String.format("asText() 输出: %s", str2));

          String str3 = data.get(strNodeName).textValue();
          System.out.println(String.format("textValue() 输出: %s", str3));

          NumberType str4 = data.get(strNodeName).numberType();
          System.out.println(String.format("numberType() 显示: %s", str4));

          System.out.println("-----------------------------------------------");
        }
      }
    }
    catch (JsonProcessingException e)
    {
      e.printStackTrace();
    }
    catch (IOException e)
    {
      e.printStackTrace();
    }
  }
}

参考资料
https://github.com/FasterXML/jackson

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