jackson json字符串、map、java对象的转换例子

jackson框架 json字符串、map、java对象的转换例子

先下载框架jar包:



下面是一些例子：

package jackson;

import java.io.File;

import java.io.FileInputStream;

import java.util.Arrays;

import java.util.HashMap;

import java.util.Iterator;

import java.util.Map;

import org.codehaus.jackson.JsonEncoding;

import org.codehaus.jackson.JsonFactory;

import org.codehaus.jackson.JsonGenerator;

import org.codehaus.jackson.JsonNode;

import org.codehaus.jackson.JsonParser;

import org.codehaus.jackson.JsonToken;

import org.codehaus.jackson.map.ObjectMapper;

import org.codehaus.jackson.node.ArrayNode;

import org.codehaus.jackson.node.ObjectNode;

import org.junit.Test;

public class Testjackson {

//@Test

public void test1(){

try{

ObjectMapper mapper = new ObjectMapper();

String jsonString = "{\"name\":\"Mahesh\", \"age\":21}";

//json字符串转对象

Student student = mapper.readValue(jsonString, Student.class);

System.out.println(student);

//对象转json字符串

jsonString = mapper.writeValueAsString(student);

System.out.println(jsonString);

//json字符串转为Map对象

Map map=mapper.readValue(jsonString, Map.class);

System.out.println(map);

}catch(Exception e) {

e.printStackTrace();

}

}

//@Test

public void test2(){

try{

Student student = new Student();

student.setAge(10);

student.setName("Mahesh");

ObjectMapper mapper = new ObjectMapper();

//将Java对象序列化到一个JSON文件

mapper.writeValue(new File("d:/student.json"), student);

System.out.println("d:/student.json文件生成结束");

//读取JSON文件转换为对象

Student student2 = mapper.readValue(new File("student.json"), Student.class);

System.out.println(student2);

}catch(Exception e) {

e.printStackTrace();

}

}

//@Test

public void test3(){

try {

ObjectMapper mapper = new ObjectMapper();

Map<String,Object> studentDataMap = new HashMap<String,Object>();

int[] marks = {1,2,3};

Student student = new Student();

student.setAge(10);

student.setName("Mahesh");

studentDataMap.put("student", student);

studentDataMap.put("name", "Mahesh Kumar");

studentDataMap.put("verified", Boolean.FALSE);

studentDataMap.put("marks", marks);

//Map转换为joson文件

mapper.writeValue(new File("d:/student2.json"), studentDataMap);

//result student.json

//{

// "student":{"name":"Mahesh","age":10},

// "marks":[1,2,3],

// "verified":false,

// "name":"Mahesh Kumar"

//}

//json文件转换为map

studentDataMap = mapper.readValue(new File("d:/student2.json"), Map.class);

System.out.println(studentDataMap.get("student"));

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

System.out.println(studentDataMap.get("verified"));

System.out.println(studentDataMap.get("marks"));

} catch (Exception e) {

e.printStackTrace();

}

}

//@Test//树遍历

public void test4(){

try {

ObjectMapper mapper = new ObjectMapper();

String jsonString = "{\"name\":\"Mahesh Kumar\", \"age\":21,\"verified\":false,\"marks\": [100,90,85]}";

JsonNode rootNode = mapper.readTree(jsonString);

JsonNode nameNode = rootNode.path("name");

System.out.println("Name: "+ nameNode.getTextValue());

JsonNode ageNode = rootNode.path("age");

System.out.println("Age: " + ageNode.getIntValue());

JsonNode verifiedNode = rootNode.path("verified");

System.out.println("Verified: " + (verifiedNode.getBooleanValue() ? "Yes":"No"));

JsonNode marksNode = rootNode.path("marks");

Iterator<JsonNode> iterator = marksNode.getElements();

System.out.print("Marks: [ ");

while (iterator.hasNext()) {

JsonNode marks = iterator.next();

System.out.print(marks.getIntValue() + " ");

}

System.out.println("]");

} catch (Exception e) {

e.printStackTrace();

}

}

//@Test//树到JSON转换

public void test5(){

try {

ObjectMapper mapper = new ObjectMapper();

JsonNode rootNode = mapper.createObjectNode();

JsonNode marksNode = mapper.createArrayNode();

((ArrayNode)marksNode).add(100);

((ArrayNode)marksNode).add(90);

((ArrayNode)marksNode).add(85);

((ObjectNode) rootNode).put("name", "Mahesh Kumar");

((ObjectNode) rootNode).put("age", 21);

((ObjectNode) rootNode).put("verified", false);

((ObjectNode) rootNode).put("marks",marksNode);

mapper.writeValue(new File("d:/student3.json"), rootNode);

rootNode = mapper.readTree(new FileInputStream("student.json"));

JsonNode nameNode = rootNode.path("name");

System.out.println("Name: "+ nameNode.getTextValue());

JsonNode ageNode = rootNode.path("age");

System.out.println("Age: " + ageNode.getIntValue());

JsonNode verifiedNode = rootNode.path("verified");

System.out.println("Verified: " + (verifiedNode.getBooleanValue() ? "Yes":"No"));

JsonNode marksNode1 = rootNode.path("marks");

Iterator<JsonNode> iterator = marksNode1.getElements();

System.out.print("Marks: [ ");

while (iterator.hasNext()) {

JsonNode marks = iterator.next();

System.out.print(marks.getIntValue() + " ");

}

System.out.println("]");

}catch (Exception e) {

e.printStackTrace();

}

}

//@Test//树到java对象

public void test6(){

try {

ObjectMapper mapper = new ObjectMapper();

JsonNode rootNode = mapper.createObjectNode();

JsonNode marksNode = mapper.createArrayNode();

((ArrayNode)marksNode).add(100);

((ArrayNode)marksNode).add(90);

((ArrayNode)marksNode).add(85);

((ObjectNode) rootNode).put("name", "Mahesh Kumar");

((ObjectNode) rootNode).put("age", 21);

((ObjectNode) rootNode).put("verified", false);

((ObjectNode) rootNode).put("marks",marksNode);

mapper.writeValue(new File("student.json"), rootNode);

rootNode = mapper.readTree(new FileInputStream("student.json"));

Student2 student = mapper.treeToValue(rootNode, Student2.class);

System.out.println("Name: "+ student.getName());

System.out.println("Age: " + student.getAge());

System.out.println("Verified: " + (student.isVerified() ? "Yes":"No"));

System.out.println("Marks: "+Arrays.toString(student.getMarks()));

} catch (Exception e) {

e.printStackTrace();

}

}

@Test//Jackson流式API

public void test7(){

try {

JsonFactory jasonFactory = new JsonFactory();

JsonGenerator jsonGenerator = jasonFactory.createJsonGenerator(new File("d:/student7.json"),

JsonEncoding.UTF8);

jsonGenerator.writeStartObject();

jsonGenerator.writeStringField("name", "Mahesh Kumar");

jsonGenerator.writeNumberField("age", 21);

jsonGenerator.writeBooleanField("verified", false);

jsonGenerator.writeFieldName("marks");

jsonGenerator.writeStartArray();

jsonGenerator.writeNumber(100);

jsonGenerator.writeNumber(90);

jsonGenerator.writeNumber(85);

jsonGenerator.writeEndArray();

jsonGenerator.writeEndObject();

jsonGenerator.close();

//result student.json

//{

// "name":"Mahesh Kumar",

// "age":21,

// "verified":false,

// "marks":[100,90,85]

//}

ObjectMapper mapper = new ObjectMapper();

Map<String,Object> dataMap = mapper.readValue(new File("d:/student7.json"), Map.class);

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

System.out.println(dataMap.get("age"));

System.out.println(dataMap.get("verified"));

System.out.println(dataMap.get("marks"));

} catch (Exception e) {

e.printStackTrace();

}

}

@Test//使用JsonParser 读取JSON

public void test8(){

try {

JsonFactory jasonFactory = new JsonFactory();

JsonGenerator jsonGenerator = jasonFactory.createJsonGenerator(new File(

"student.json"), JsonEncoding.UTF8);

jsonGenerator.writeStartObject();

jsonGenerator.writeStringField("name", "Mahesh Kumar");

jsonGenerator.writeNumberField("age", 21);

jsonGenerator.writeBooleanField("verified", false);

jsonGenerator.writeFieldName("marks");

jsonGenerator.writeStartArray();

jsonGenerator.writeNumber(100);

jsonGenerator.writeNumber(90);

jsonGenerator.writeNumber(85);

jsonGenerator.writeEndArray();

jsonGenerator.writeEndObject();

jsonGenerator.close();

//result student.json

//{

// "name":"Mahesh Kumar",

// "age":21,

// "verified":false,

// "marks":[100,90,85]

//}

JsonParser jsonParser = jasonFactory.createJsonParser(new File("d:/student7.json"));

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

//get the current token

String fieldname = jsonParser.getCurrentName();

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

//move to next token

jsonParser.nextToken();

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

}

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

//move to next token

jsonParser.nextToken();

System.out.println(jsonParser.getNumberValue());

}

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

//move to next token

jsonParser.nextToken();

System.out.println(jsonParser.getBooleanValue());

}

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

//move to [

jsonParser.nextToken();

// loop till token equal to "]"

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

System.out.println(jsonParser.getNumberValue());

}

}

}

} catch (Exception e) {

e.printStackTrace();

}

}

}

class Student2 {

String name;

int age;

boolean verified;

int[] marks;

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public int getAge() {

return age;

}

public void setAge(int age) {

this.age = age;

}

public boolean isVerified() {

return verified;

}

public void setVerified(boolean verified) {

this.verified = verified;

}

public int[] getMarks() {

return marks;

}

public void setMarks(int[] marks) {

this.marks = marks;

}

}