應用Jackson來完成Java對象與JSON的互相轉換的教程。本站提示廣大學習愛好者：（應用Jackson來完成Java對象與JSON的互相轉換的教程）文章只能為提供參考，不一定能成為您想要的結果。以下是應用Jackson來完成Java對象與JSON的互相轉換的教程正文
1、入門
Jackson中有個ObjectMapper類很是適用，用於Java對象與JSON的交換。
1.JAVA對象轉JSON[JSON序列化]
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("小平易近");
user.setEmail("[email protected]");
user.setAge(20);
SimpleDateFormat dateformat = new SimpleDateFormat("yyyy-MM-dd");
user.setBirthday(dateformat.parse("1996-10-01"));
/**
* ObjectMapper是JSON操作的焦點，Jackson的一切JSON操作都是在ObjectMapper中完成。
* ObjectMapper有多個JSON序列化的辦法，可以把JSON字符串保留File、OutputStream等分歧的介質中。
* writeValue(File arg0, Object arg1)把arg1轉成json序列，並保留到arg0文件中。
* writeValue(OutputStream arg0, Object arg1)把arg1轉成json序列，並保留到arg0輸入流中。
* writeValueAsBytes(Object arg0)把arg0轉成json序列，並把成果輸入成字節數組。
* writeValueAsString(Object arg0)把arg0轉成json序列，並把成果輸入成字符串。
*/
ObjectMapper mapper = new ObjectMapper();
//User類轉JSON
//輸入成果：{"name":"小平易近","age":20,"birthday":844099200000,"email":"[email protected]"}
String json = mapper.writeValueAsString(user);
System.out.println(json);
//Java聚集轉JSON
//輸入成果：[{"name":"小平易近","age":20,"birthday":844099200000,"email":"[email protected]"}]
List<User> users = new ArrayList<User>();
users.add(user);
String jsonlist = mapper.writeValueAsString(users);
System.out.println(jsonlist);
}
}
2.JSON轉Java類[JSON反序列化]
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\":\"小平易近\",\"age\":20,\"birthday\":844099200000,\"email\":\"[email protected]\"}";
/**
* ObjectMapper支撐從byte[]、File、InputStream、字符串等數據的JSON反序列化。
*/
ObjectMapper mapper = new ObjectMapper();
User user = mapper.readValue(json, User.class);
System.out.println(user);
}
}
2、Jackson支撐3種應用方法:
1、Data Binding：最便利應用.
(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到一個實體類中.
System.out.println(user.getName());
System.out.println(user.getType());
}
Model類：
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<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
*/
public void rawDataBinding() throws Exception{
ObjectMapper mapper = new ObjectMapper();
HashMap map = mapper.readValue(MODEL_BINDING,HashMap.class);//readValue到一個原始數據類型.
System.out.println(map.get("name"));
System.out.println(map.get("type"));
}
(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<String,Model> modelMap = mapper.readValue(GENERIC_BINDING,new TypeReference<HashMap<String,Model>>(){});//readValue到一個范型數據中.
Model model = modelMap.get("key2");
System.out.println(model.getName());
System.out.println(model.getType());
}
2、Tree Model：最靈巧。
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與get感化雷同,然則當找不到該節點的時刻,前往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);
//創立根節點
ObjectNode root = mapper.createObjectNode();
//創立子節點1
ObjectNode node1 = mapper.createObjectNode();
node1.put("nodekey1",1);
node1.put("nodekey2",2);
//綁定子節點1
root.put("child",node1);
//數組節點
ArrayNode arrayNode = mapper.createArrayNode();
arrayNode.add(node1);
arrayNode.add(1);
//綁定命組節點
root.put("arraynode", arrayNode);
//JSON讀到樹節點
JsonNode valueToTreeNode = mapper.valueToTree(TREE_MODEL_BINDING);
//綁定JSON節點
root.put("valuetotreenode",valueToTreeNode);
//JSON綁定到JSON節點對象
JsonNode bindJsonNode = mapper.readValue(GENERIC_BINDING, JsonNode.class);//綁定JSON到JSON節點對象.
//綁定JSON節點
root.put("bindJsonNode",bindJsonNode);
System.out.println(mapper.writeValueAsString(root));
}
3、Streaming API：最好機能。
關於機能請求高的法式,推舉應用流API,不然應用其他辦法
不論是創立JsonGenerator照樣JsonParser,都是應用JsonFactory。
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();
}
}
