Jackson 2 Convert Java Object to / from JSON
In this tutorial, we will show you how to use Jackson 2.x to convert Java objects to / from a JSON.
1. Basic
1.1 Convert a Staff object to from JSON.
writeValue(...) – Java Objects to JSON
ObjectMapper mapper = new ObjectMapper(); // Java object to JSON file mapper.writeValue(new File("c:\\test\\staff.json"), new Staff()); // Java object to JSON string String jsonString = mapper.writeValueAsString(object);
readValue(...) – JSON to Java Objects
ObjectMapper mapper = new ObjectMapper(); //JSON file to Java object Staff obj = mapper.readValue(new File("c:\\test\\staff.json"), Staff.class); //JSON URL to Java object Staff obj = mapper.readValue(new URL("http://some-domains/api/name.json"), Staff.class); //JSON string to Java Object Staff obj = mapper.readValue("{'name' : 'mkyong'}", Staff.class);
P.S Tested with Jackson 2.9.8
Read this How to parse JSON with Jackson, containing Jackson examples like Object to/from JSON, @JsonView, @JsonProperty, @JsonInclude, @JsonIgnore, and some FAQs.
1. Download Jackson
1.1 Declares jackson-databind, it will pull in jackson-annotations and jackson-core
<dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-databind</artifactId> <version>2.9.8</version> </dependency>
1.2 Review the Jackson dependencies :
$ mvn dependency:tree \- com.fasterxml.jackson.core:jackson-databind:jar:2.9.8:compile [INFO] +- com.fasterxml.jackson.core:jackson-annotations:jar:2.9.0:compile [INFO] \- com.fasterxml.jackson.core:jackson-core:jar:2.9.8:compile
Most of the APIs still maintains the same method name and signature, just the packaging is different.
- Jackson 1.x – org.codehaus.jackson.map
- Jackson 2.x – com.fasterxml.jackson.databind
2. POJO
A simple Java object for testing.
public class Staff { private String name; private int age; private String[] position; // Array private List<String> skills; // List private Map<String, BigDecimal> salary; // Map // getters , setters, some boring stuff
3. Java Objects to JSON
package com.mkyong; import com.fasterxml.jackson.databind.ObjectMapper; import java.io.File; import java.io.IOException; import java.math.BigDecimal; import java.util.Arrays; import java.util.HashMap; import java.util.Map; public class JacksonExample1 { public static void main(String[] args) { ObjectMapper mapper = new ObjectMapper(); Staff staff = createStaff(); try { // Java objects to JSON file mapper.writeValue(new File("c:\\test\\staff.json"), staff); // Java objects to JSON string - compact-print String jsonString = mapper.writeValueAsString(staff); System.out.println(jsonString); // Java objects to JSON string - pretty-print String jsonInString2 = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(staff); System.out.println(jsonInString2); } catch (IOException e) { e.printStackTrace(); private static Staff createStaff() { Staff staff = new Staff(); staff.setName("mkyong"); staff.setAge(38); staff.setPosition(new String[]{"Founder", "CTO", "Writer"}); Map<String, BigDecimal> salary = new HashMap() {{ put("2010", new BigDecimal(10000)); put("2012", new BigDecimal(12000)); put("2018", new BigDecimal(14000)); }}; staff.setSalary(salary); staff.setSkills(Arrays.asList("java", "python", "node", "kotlin")); return staff;
Output
{"name":"mkyong","age":38,"position":["Founder","CTO","Writer"],"skills":["java","python","node","kotlin"],"salary":{"2018":14000,"2012":12000,"2010":10000}}
{"name":"mkyong","age":38,"position":["Founder","CTO","Writer"],"skills":["java","python","node","kotlin"],"salary":{"2018":14000,"2012":12000,"2010":10000}} "name" : "mkyong", "age" : 38, "position" : [ "Founder", "CTO", "Writer" ], "skills" : [ "java", "python", "node", "kotlin" ], "salary" : { "2018" : 14000, "2012" : 12000, "2010" : 10000
4. JSON to Java Object
package com.mkyong; import com.fasterxml.jackson.databind.ObjectMapper; import java.io.File; import java.io.IOException; public class JacksonExample2 { public static void main(String[] args) { ObjectMapper mapper = new ObjectMapper(); try { // JSON file to Java object Staff staff = mapper.readValue(new File("c:\\test\\staff.json"), Staff.class); // JSON string to Java object String jsonInString = "{\"name\":\"mkyong\",\"age\":37,\"skills\":[\"java\",\"python\"]}"; Staff staff2 = mapper.readValue(jsonInString, Staff.class); // compact print System.out.println(staff2); // pretty print String prettyStaff1 = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(staff2); System.out.println(prettyStaff1); } catch (IOException e) { e.printStackTrace();
Output
Staff{name='mkyong', age=37, position=null, skills=[java, python], salary=null} "name" : "mkyong", "age" : 37, "position" : null, "skills" : [ "java", "python" ], "salary" : null
More Jackson examples read this – How to parse JSON with Jackson