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;

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/**
* 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)
{
}
}

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/**
* 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)
{
}
}

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/**
* 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)
{

}
}

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/**
* 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)
{

}
}

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// 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);

参考资料

https://github.com/FasterXML/jackson

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

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