Jacksonを使用してJavaオブジェクトとJSONの相互変換を実現するチュートリアル
10216 ワード
一、入門JacksonにはObjectMapperクラスがあり、JavaオブジェクトとJSONの交換に使用されています.1.JAVA対象転JSON[JSONシーケンス化]
2.JSON回転Java類[JSON逆シーケンス化]
二、Jacksonは3種類の使用方式をサポートする:1、Data Binding:最も使いやすい.(1)Full Data Binding:
Modelクラス:
(2)Raw Data Binding:
(3)generic Data Binding:
2、Tree Model:最も柔軟です.
3、Streaming API:最適な性能.パフォーマンスが要求されるプログラムでは、ストリームAPIの使用を推奨します.そうしないと、JsonGeneratorの作成にかかわらず、JsonParserの作成にかかわらず、JsonFactoryを使用する他の方法が推奨されます.
import java.io.IOException;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import com.fasterxml.jackson.databind.ObjectMapper;
public class JacksonDemo {
public static void main(String[] args) throws ParseException, IOException {
User user = new User();
user.setName(" ");
user.setEmail("[email protected]");
user.setAge(20);
SimpleDateFormat dateformat = new SimpleDateFormat("yyyy-MM-dd");
user.setBirthday(dateformat.parse("1996-10-01"));
/**
* ObjectMapper JSON ,Jackson JSON ObjectMapper 。
* ObjectMapper JSON , JSON File、OutputStream 。
* writeValue(File arg0, Object arg1) arg1 json , arg0 。
* writeValue(OutputStream arg0, Object arg1) arg1 json , arg0 。
* writeValueAsBytes(Object arg0) arg0 json , 。
* writeValueAsString(Object arg0) arg0 json , 。
*/
ObjectMapper mapper = new ObjectMapper();
//User JSON
// :{"name":" ","age":20,"birthday":844099200000,"email":"[email protected]"}
String json = mapper.writeValueAsString(user);
System.out.println(json);
//Java JSON
// :[{"name":" ","age":20,"birthday":844099200000,"email":"[email protected]"}]
List users = new ArrayList();
users.add(user);
String jsonlist = mapper.writeValueAsString(users);
System.out.println(jsonlist);
}
}
2.JSON回転Java類[JSON逆シーケンス化]
import java.io.IOException;
import java.text.ParseException;
import com.fasterxml.jackson.databind.ObjectMapper;
public class JacksonDemo {
public static void main(String[] args) throws ParseException, IOException {
String json = "{\"name\":\" \",\"age\":20,\"birthday\":844099200000,\"email\":\"[email protected]\"}";
/**
* ObjectMapper byte[]、File、InputStream、 JSON 。
*/
ObjectMapper mapper = new ObjectMapper();
User user = mapper.readValue(json, User.class);
System.out.println(user);
}
}
二、Jacksonは3種類の使用方式をサポートする:1、Data Binding:最も使いやすい.(1)Full Data Binding:
private static final String MODEL_BINDING = "{\"name\":\"name1\",\"type\":1}";
public void fullDataBinding() throws Exception{
ObjectMapper mapper = new ObjectMapper();
Model user = mapper.readValue(MODEL_BINDING, Model.class);//readValue .
System.out.println(user.getName());
System.out.println(user.getType());
}
Modelクラス:
private static class Model{
private String name;
private int type;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getType() {
return type;
}
public void setType(int type) {
this.type = type;
}
}
(2)Raw Data Binding:
/**
Concrete Java types that Jackson will use for simple data binding are:
JSON Type Java Type
object LinkedHashMap
array ArrayList
(3)generic Data Binding:
private static final String GENERIC_BINDING = "{\"key1\":{\"name\":\"name2\",\"type\":2},\"key2\":{\"name\":\"name3\",\"type\":3}}";
public void genericDataBinding() throws Exception{
ObjectMapper mapper = new ObjectMapper();
HashMap modelMap = mapper.readValue(GENERIC_BINDING,new TypeReference>(){});//readValue .
Model model = modelMap.get("key2");
System.out.println(model.getName());
System.out.println(model.getType());
}
2、Tree Model:最も柔軟です.
private static final String TREE_MODEL_BINDING = "{\"treekey1\":\"treevalue1\",\"treekey2\":\"treevalue2\",\"children\":[{\"childkey1\":\"childkey1\"}]}";
public void treeModelBinding() throws Exception{
ObjectMapper mapper = new ObjectMapper();
JsonNode rootNode = mapper.readTree(TREE_MODEL_BINDING);
//path get , , missing node 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);
//
ObjectNode root = mapper.createObjectNode();
// 1
ObjectNode node1 = mapper.createObjectNode();
node1.put("nodekey1",1);
node1.put("nodekey2",2);
// 1
root.put("child",node1);
//
ArrayNode arrayNode = mapper.createArrayNode();
arrayNode.add(node1);
arrayNode.add(1);
//
root.put("arraynode", arrayNode);
//JSON
JsonNode valueToTreeNode = mapper.valueToTree(TREE_MODEL_BINDING);
// JSON
root.put("valuetotreenode",valueToTreeNode);
//JSON JSON
JsonNode bindJsonNode = mapper.readValue(GENERIC_BINDING, JsonNode.class);// JSON JSON .
// JSON
root.put("bindJsonNode",bindJsonNode);
System.out.println(mapper.writeValueAsString(root));
}
3、Streaming API:最適な性能.パフォーマンスが要求されるプログラムでは、ストリームAPIの使用を推奨します.そうしないと、JsonGeneratorの作成にかかわらず、JsonParserの作成にかかわらず、JsonFactoryを使用する他の方法が推奨されます.
package com.jingshou.jackson;
import java.io.File;
import java.io.IOException;
import com.fasterxml.jackson.core.JsonEncoding;
import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
public class JacksonTest6 {
public static void main(String[] args) throws IOException {
JsonFactory jfactory = new JsonFactory();
/*** write to file ***/
JsonGenerator jGenerator = jfactory.createGenerator(new File(
"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(new File("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();
}
}