How to parse JSON string with Jackson
This article uses the Jackson framework to parse JSON strings in Java.
Table of contents:
- 1. Download Jackson
- 2. Parse JSON String with Jackson
- 3. Parse JSON Array with Jackson
- 4. Convert Java Object to JSON String
- 5. Convert JSON String to Java Object
- 6. Download Source Code
- 7. References
P.S Tested with Jackson 2.17.0
1. Download Jackson
Simply declare jackson-databind in the pom.xml, and it will automatically pull in jackson-annotations, jackson-core, and other necessary dependencies.
pom.xml
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.17.0</version>
</dependency>
Terminal
$ mvn dependency:tree
[INFO] +- com.fasterxml.jackson.core:jackson-databind:jar:2.17.0:compile
[INFO] | +- com.fasterxml.jackson.core:jackson-annotations:jar:2.17.0:compile
[INFO] | +- com.fasterxml.jackson.core:jackson-core:jar:2.17.0:compile
[INFO] | \- net.bytebuddy:byte-buddy:jar:1.14.9:compile
[INFO] \- com.fasterxml.jackson.datatype:jackson-datatype-jsr310:jar:2.17.0:compile
2. Parse JSON String with Jackson
A simple JSON string.
{
"name": "mkyong",
"age": 20
}
BasicJsonStringExample
package com.mkyong.json.jackson;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
public class BasicJsonStringExample {
public static void main(String[] args) {
try {
// a simple JSON string
String json = "{\"name\": \"mkyong\", \"age\": 20}";
// Jackson main object
ObjectMapper mapper = new ObjectMapper();
// read the json strings and convert it into JsonNode
JsonNode node = mapper.readTree(json);
// display the JsonNode
System.out.println("Name: " + node.get("name").asText());
System.out.println("Age: " + node.get("age").asInt());
} catch (JsonProcessingException e) {
throw new RuntimeException(e);
}
}
}
output
Name: mkyong
Age: 20
3. Parse JSON Array with Jackson
Array of JSON objects.
[
{
"name": "mkyong",
"age": 20
},
{
"name": "ah pig",
"age": 40
},
{
"name": "ah dog",
"age": 30
}
]
BasicJsonArrayExample.java
package com.mkyong.json.jackson;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
public class BasicJsonArrayExample {
public static void main(String[] args) {
try {
// a simple JSON array
String json = "[" +
"{\"name\": \"mkyong\", \"age\": 20}," +
"{\"name\": \"ah pig\", \"age\": 40}," +
"{\"name\": \"ag dog\", \"age\": 30}" +
"]";
// Jackson main object
ObjectMapper mapper = new ObjectMapper();
// read the json strings and convert it into JsonNode
JsonNode arrayNode = mapper.readTree(json);
// is this a array?
if (arrayNode.isArray()) {
// yes, loop the JsonNode and display one by one
for (JsonNode node : arrayNode) {
System.out.println("Name: " + node.get("name").asText());
System.out.println("Age: " + node.get("age").asInt());
}
}
} catch (JsonProcessingException e) {
throw new RuntimeException(e);
}
}
}
output
Name: mkyong
Age: 20
Name: ah pig
Age: 40
Name: ag dog
Age: 30
4. Convert Java Object to JSON String
This example uses Jackson to convert a Java object Staff into a file named output.json and a Java String and print it to the console.
Staff.java
package com.mkyong.json.model;
import java.math.BigDecimal;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
public class Staff {
private String name;
private int age;
private String[] position; // Array
private List<String> skills; // List
private Map<String, BigDecimal> salary; // Map
private boolean active; // boolean
// getter, setters, constructor and etc...
}
ConvertJavaObjectToJsonExample.java
package com.mkyong.json.jackson;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.mkyong.json.model.Staff;
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 ConvertJavaObjectToJsonExample {
private static final ObjectMapper MAPPER = new ObjectMapper();
public static void main(String[] args) throws IOException {
Staff staff = createStaff();
// Java object to JSON file - default compact-print
// MAPPER.writeValue(new File("output.json"), staff);
// write Java object to JSON file with pretty print
MAPPER.writerWithDefaultPrettyPrinter()
.writeValue(new File("output.json"), staff);
// convert Java object to JSON string - default compact-print
String jsonString = MAPPER.writeValueAsString(staff);
System.out.println(jsonString);
// convert Java object to JSON string - with json pretty-print
String jsonStringPrettyPrint = MAPPER
.writerWithDefaultPrettyPrinter()
.writeValueAsString(staff);
System.out.println(jsonStringPrettyPrint);
}
private static Staff createStaff() {
Staff staff = new Staff();
staff.setName("mkyong");
staff.setAge(42);
staff.setPosition(new String[]{"Founder", "CTO", "Writer", "Minimalists"});
Map<String, BigDecimal> salary = new HashMap<>();
salary.put("2010", new BigDecimal(10000));
salary.put("2012", new BigDecimal(12000));
salary.put("2018", new BigDecimal(14000));
staff.setSalary(salary);
staff.setSkills(Arrays.asList("java", "python", "node", "kotlin"));
return staff;
}
}
output
output.json
{
"name" : "mkyong",
"age" : 42,
"position" : [ "Founder", "CTO", "Writer", "Minimalists" ],
"skills" : [ "java", "python", "node", "kotlin" ],
"salary" : {
"2018" : 14000,
"2012" : 12000,
"2010" : 10000
},
"active" : false
}
5. Convert JSON String to Java Object
This example uses Jackson to read JSON from a file and strings and convert it to a Java object.
output.json
{
"name" : "mkyong",
"age" : 42,
"position" : [ "Founder", "CTO", "Writer", "Minimalists" ],
"skills" : [ "java", "python", "node", "kotlin" ],
"salary" : {
"2018" : 14000,
"2012" : 12000,
"2010" : 10000
},
"active" : false
}
ConvertJsonToJavaObjectExample.java
package com.mkyong.json.jackson;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.mkyong.json.model.Staff;
import java.io.File;
import java.io.IOException;
public class ConvertJsonToJavaObjectExample {
private static final ObjectMapper MAPPER = new ObjectMapper();
public static void main(String[] args) throws IOException {
// Convert JSON file to Java object
Staff staff = MAPPER.readValue(new File("output.json"), Staff.class);
System.out.println(staff);
// Convert JSON string to Java object
String jsonInString = "{\"name\":\"mkyong\",\"age\":37,\"skills\":[\"java\",\"python\"]}";
Staff staff2 = MAPPER.readValue(jsonInString, Staff.class);
// convert compact to pretty-print
String staff2PrettyPrint = MAPPER
.writerWithDefaultPrettyPrinter()
.writeValueAsString(staff2);
System.out.println(staff2PrettyPrint);
}
}
output
Staff{name='mkyong', age=42, position=[Founder, CTO, Writer, Minimalists],
skills=[java, python, node, kotlin], salary={2018=14000, 2012=12000, 2010=10000},
active=false}
{
"name" : "mkyong",
"age" : 37,
"position" : null,
"skills" : [ "java", "python" ],
"salary" : null,
"active" : false
}
6. Download Source Code
$ git clone https://github.com/mkyong/java-json
7. References
About Author
Founder of Mkyong.com, love Java and open source stuff. Follow him on Twitter. If you like my tutorials, consider make a donation to these charities.
Comments
Subscribe
0 Comments