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<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)    {    }  }

 

/**   * 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();    }

参考资料

https://github.com/FasterXML/jackson

 

blog.csdn.net/joyous/article/details/9448461
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