Jackson provide Java api’s to create JSON on runtime . These api’s can handle different type of data and objects.
Jacson API’s
Writing Root Object JsonGenerator.writeStartObject(); JsonGenerator.writeEndObject(); Writing Sub Object JsonGenerator.writeObjectFieldStart(); JsonGenerator.writeEndObject(); Writing Array JsonGenerator.writeArrayFieldStart() JsonGenerator.writeEndObject(); Writing Field Level JsonGenerator.writeNumberField(); JsonGenerator.writeStringField(); JsonGenerator.writeBooleanField();
Pre-Requisite
Add below jackson-databind-2.8.5.jar in your classpath or make dependency entry in pom.xml file.
<dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-databind</artifactId> <version>2.8.5</version> </dependency>
Example
In below example by Jacson API’s generating JSON on runtime and writing on file.
package test.facingissesonit.json.jacson;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.util.DefaultPrettyPrinter;
public class JsonStreamWriteToFile {
public static void main(String[] args) {
Student student = sampleStudentObject();
try {
JsonGenerator jsonGenerator = new JsonFactory().createGenerator(new FileOutputStream("student_data.txt"));
// for pretty formatted printing
jsonGenerator.setPrettyPrinter(new DefaultPrettyPrinter());
// start root from here
jsonGenerator.writeStartObject();
jsonGenerator.writeNumberField("rollNumber", student.getRollNumber());
jsonGenerator.writeStringField("firstName", student.getFirstName());
jsonGenerator.writeStringField("lastName", student.getLastName());
jsonGenerator.writeBooleanField("permanent", student.isPermanent());
jsonGenerator.writeObjectFieldStart("address"); // object writing
jsonGenerator.writeStringField("addressLine", student.getAddress().getAddressLine());
jsonGenerator.writeStringField("city", student.getAddress().getCity());
jsonGenerator.writeNumberField("zipCode", student.getAddress().getZipCode());
jsonGenerator.writeEndObject(); // address object completed
jsonGenerator.writeArrayFieldStart("phoneNumbers");
for (long num : student.getPhoneNumbers())
jsonGenerator.writeNumber(num);
jsonGenerator.writeEndArray();
// start array writing for cities
jsonGenerator.writeArrayFieldStart("cities");
for (String city : student.getCities())
jsonGenerator.writeString(city);
// closing cities array
jsonGenerator.writeEndArray();
jsonGenerator.writeObjectFieldStart("properties");
Set<String> keySet = student.getProperties().keySet();
for (String key : keySet) {
String value = student.getProperties().get(key);
jsonGenerator.writeStringField(key, value);
}
// End of properties writing
jsonGenerator.writeEndObject();
//End root object writing
jsonGenerator.writeEndObject();
jsonGenerator.flush();
jsonGenerator.close();
} catch (IOException ex) {
ex.printStackTrace();
}
}
public static Student sampleStudentObject() {
Student student = new Student();
student.setRollNumber(11);
student.setFirstName("Saurabh");
student.setLastName("Gupta");
student.setPhoneNumbers(new long[] { 2233445566L, 3344556677L });
Address add = new Address();
add.setAddressLine("Lake Union Hill Way");
add.setCity("Atlanta");
add.setState("GA");
add.setZipCode(50005);
student.setAddress(add);
List<String> cities = new ArrayList<String>();
cities.add("Dallas");
cities.add("San Antonio");
cities.add("Irving");
student.setCities(cities);
Map<String, String> props = new HashMap<String, String>();
props.put("age", "34 years");
props.put("interst", "Math");
props.put("play", "Badminton");
student.setProperties(props);
return student;
}
}
Model Object
Student and Address classes are required to execute these code
package test.facingissesonit.json.jacson;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
public class Student {
private int rollNumber;
private String firstName;
private String lastName;
private boolean permanent;
private Address address;
private long[] phoneNumbers;
private List<String> cities;
private Map<String, String> properties;
@Override
public String toString()
{
StringBuffer sb=new StringBuffer();
sb.append("==============Student Information================\n");
sb.append("rollNumber=").append(rollNumber).append("\n");
sb.append("firstName=").append(firstName).append("\n");
sb.append("lastName=").append(lastName).append("\n");
sb.append("permanent=").append(permanent).append("\n");
sb.append("adress=").append(address).append("\n");
sb.append("phoneNumbers=").append(Arrays.toString(phoneNumbers)).append("\n");
sb.append("cities=").append(Arrays.toString(cities.toArray(new String[cities.size()]))).append("\n");
sb.append("properties=").append(properties).append("\n");
return sb.toString();
}
public int getRollNumber() {
return rollNumber;
}
public void setRollNumber(int rollNumber) {
this.rollNumber = rollNumber;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public boolean isPermanent() {
return permanent;
}
public void setPermanent(boolean permanent) {
this.permanent = permanent;
}
public Address getAddress() {
return address;
}
public void setAddress(Address address) {
this.address = address;
}
public long[] getPhoneNumbers() {
return phoneNumbers;
}
public void setPhoneNumbers(long[] phoneNumbers) {
this.phoneNumbers = phoneNumbers;
}
public List<String> getCities() {
return cities;
}
public void setCities(List<String> cities) {
this.cities = cities;
}
public Map<String, String> getProperties() {
return properties;
}
public void setProperties(Map<String, String> properties) {
this.properties = properties;
}
}
package test.facingissesonit.json.jacson;
public class Address {
private String addressLine;
private String city;
private String state;
private int zipCode;
@Override
public String toString()
{
StringBuffer sb=new StringBuffer();
sb.append("AddressLine=").append(addressLine).append("\n");
sb.append("city=").append(city).append("\n");
sb.append("state=").append(state).append("\n");
sb.append("zipCode=").append(zipCode).append("\n");
return sb.toString();
}
public String getAddressLine() {
return addressLine;
}
public void setAddressLine(String addressLine) {
this.addressLine = addressLine;
}
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
public String getState() {
return state;
}
public void setState(String state) {
this.state = state;
}
public int getZipCode() {
return zipCode;
}
public void setZipCode(int zipCode) {
this.zipCode = zipCode;
}
}
Output
Generated output on Student_data.txt file
{
"rollNumber" : 11,
"firstName" : "Saurabh",
"lastName" : "Gupta",
"permanent" : false,
"address" : {
"addressLine" : "Lake Union Hill Way",
"city" : "Atlanta",
"zipCode" : 50005
},
"phoneNumbers" : [ 2233445566, 3344556677 ],
"cities" : [ "Dallas", "San Antonio", "Irving" ],
"properties" : {
"play" : "Badminton",
"interst" : "Math",
"age" : "34 years"
}
}
More Sample Code
For more java and JDBC codes follow below links
Facing Issues On IT 