使用Jackson来实现Java对象与JSON的相互转换的教程

importjava.io.IOException;

importjava.text.ParseException;

importjava.text.SimpleDateFormat;

importcom.fasterxml.jackson.databind.ObjectMapper;

publicclassJacksonDemo {

publicstaticvoidmain(String[] args)throwsParseException, IOException {

User user =newUser();

user.setName("小民");

user.setEmail("xiaomin@sina.com");

user.setAge(20);

SimpleDateFormat dateformat =newSimpleDateFormat("yyyy-MM-dd");

user.setBirthday(dateformat.parse("1996-10-01"));

/**

* ObjectMapper是JSON操作的核心，Jackson的所有JSON操作都是在ObjectMapper中实现。

* ObjectMapper有多个JSON序列化的方法，可以把JSON字符串保存File、OutputStream等不同的介质中。

* writeValue(File arg0, Object arg1)把arg1转成json序列，并保存到arg0文件中。

* writeValue(OutputStream arg0, Object arg1)把arg1转成json序列，并保存到arg0输出流中。

* writeValueAsBytes(Object arg0)把arg0转成json序列，并把结果输出成字节数组。

* writeValueAsString(Object arg0)把arg0转成json序列，并把结果输出成字符串。

*/

ObjectMapper mapper =newObjectMapper();

//User类转JSON

//输出结果：{"name":"小民","age":20,"birthday":844099200000,"email":"xiaomin@sina.com"}

String json = mapper.writeValueAsString(user);

System.out.println(json);

//Java集合转JSON

//输出结果：[{"name":"小民","age":20,"birthday":844099200000,"email":"xiaomin@sina.com"}]

List<User> users =newArrayList<User>();

users.add(user);

String jsonlist = mapper.writeValueAsString(users);

System.out.println(jsonlist);

}

}

importjava.io.IOException;

importjava.text.ParseException;

importcom.fasterxml.jackson.databind.ObjectMapper;

publicclassJacksonDemo {

publicstaticvoidmain(String[] args)throwsParseException, IOException {

String json ="{\"name\":\"小民\",\"age\":20,\"birthday\":844099200000,\"email\":\"xiaomin@sina.com\"}";

/**

* ObjectMapper支持从byte[]、File、InputStream、字符串等数据的JSON反序列化。

*/

ObjectMapper mapper =newObjectMapper();

User user = mapper.readValue(json, User.class);

System.out.println(user);

}

}

privatestaticfinalString MODEL_BINDING ="{\"name\":\"name1\",\"type\":1}";

publicvoidfullDataBinding()throwsException{

ObjectMapper mapper =newObjectMapper();

Model user = mapper.readValue(MODEL_BINDING, Model.class);//readValue到一个实体类中.

System.out.println(user.getName());

System.out.println(user.getType());

}

privatestaticclassModel{

privateString name;

privateinttype;

publicString getName() {

returnname;

}

publicvoidsetName(String name) {

this.name = name;

}

publicintgetType() {

returntype;

}

publicvoidsetType(inttype) {

this.type = type;

}

}

/**

Concrete Java types that Jackson will use for simple data binding are:

JSON Type Java Type

object LinkedHashMap<String,Object>

array ArrayList<Object>

string String

number(no fraction) Integer, Long or BigInteger (smallest applicable)

number(fraction) Double(configurable to use BigDecimal)

true|false Boolean

null null

*/

publicvoidrawDataBinding()throwsException{

ObjectMapper mapper =newObjectMapper();

HashMap map = mapper.readValue(MODEL_BINDING,HashMap.class);//readValue到一个原始数据类型.

System.out.println(map.get("name"));

System.out.println(map.get("type"));

}

privatestaticfinalString GENERIC_BINDING ="{\"key1\":{\"name\":\"name2\",\"type\":2},\"key2\":{\"name\":\"name3\",\"type\":3}}";

publicvoidgenericDataBinding()throwsException{

ObjectMapper mapper =newObjectMapper();

HashMap<String,Model> modelMap = mapper.readValue(GENERIC_BINDING,newTypeReference<HashMap<String,Model>>(){});//readValue到一个范型数据中.

Model model = modelMap.get("key2");

System.out.println(model.getName());

System.out.println(model.getType());

}

privatestaticfinalString TREE_MODEL_BINDING ="{\"treekey1\":\"treevalue1\",\"treekey2\":\"treevalue2\",\"children\":[{\"childkey1\":\"childkey1\"}]}";

publicvoidtreeModelBinding()throwsException{

ObjectMapper mapper =newObjectMapper();

JsonNode rootNode = mapper.readTree(TREE_MODEL_BINDING);

//path与get作用相同,但是当找不到该节点的时候,返回missing node而不是Null.

String treekey2value = rootNode.path("treekey2").getTextValue();//

System.out.println("treekey2value:"+ treekey2value);

JsonNode childrenNode = rootNode.path("children");

String childkey1Value = childrenNode.get(0).path("childkey1").getTextValue();

System.out.println("childkey1Value:"+childkey1Value);

//创建根节点

ObjectNode root = mapper.createObjectNode();

//创建子节点1

ObjectNode node1 = mapper.createObjectNode();

node1.put("nodekey1",1);

node1.put("nodekey2",2);

//绑定子节点1

root.put("child",node1);

//数组节点

ArrayNode arrayNode = mapper.createArrayNode();

arrayNode.add(node1);

arrayNode.add(1);

//绑定数组节点

root.put("arraynode", arrayNode);

//JSON读到树节点

JsonNode valueToTreeNode = mapper.valueToTree(TREE_MODEL_BINDING);

//绑定JSON节点

root.put("valuetotreenode",valueToTreeNode);

//JSON绑定到JSON节点对象

JsonNode bindJsonNode = mapper.readValue(GENERIC_BINDING, JsonNode.class);//绑定JSON到JSON节点对象.

//绑定JSON节点

root.put("bindJsonNode",bindJsonNode);

System.out.println(mapper.writeValueAsString(root));

}

packagecom.jingshou.jackson;

importjava.io.File;

importjava.io.IOException;

importcom.fasterxml.jackson.core.JsonEncoding;

importcom.fasterxml.jackson.core.JsonFactory;

importcom.fasterxml.jackson.core.JsonGenerator;

importcom.fasterxml.jackson.core.JsonParser;

importcom.fasterxml.jackson.core.JsonToken;

publicclassJacksonTest6 {

publicstaticvoidmain(String[] args)throwsIOException {

JsonFactory jfactory =newJsonFactory();

/*** write to file ***/

JsonGenerator jGenerator = jfactory.createGenerator(newFile(

"c:\\user.json"), JsonEncoding.UTF8);

jGenerator.writeStartObject();// {

jGenerator.writeStringField("name","mkyong");// "name" : "mkyong"

jGenerator.writeNumberField("age",29);// "age" : 29

jGenerator.writeFieldName("messages");// "messages" :

jGenerator.writeStartArray();// [

jGenerator.writeString("msg 1");// "msg 1"

jGenerator.writeString("msg 2");// "msg 2"

jGenerator.writeString("msg 3");// "msg 3"

jGenerator.writeEndArray();// ]

jGenerator.writeEndObject();// }

jGenerator.close();

/*** read from file ***/

JsonParser jParser = jfactory.createParser(newFile("c:\\user.json"));

// loop until token equal to "}"

while(jParser.nextToken() != JsonToken.END_OBJECT) {

String fieldname = jParser.getCurrentName();

if("name".equals(fieldname)) {

// current token is "name",

// move to next, which is "name"'s value

jParser.nextToken();

System.out.println(jParser.getText());// display mkyong

}

if("age".equals(fieldname)) {

// current token is "age",

// move to next, which is "name"'s value

jParser.nextToken();

System.out.println(jParser.getIntValue());// display 29

}

if("messages".equals(fieldname)) {

jParser.nextToken();// current token is "[", move next

// messages is array, loop until token equal to "]"

while(jParser.nextToken() != JsonToken.END_ARRAY) {

// display msg1, msg2, msg3

System.out.println(jParser.getText());

}

}

}

jParser.close();

}

}