Spring REST 2: POJO JSON Conversion

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Spring and Jackson Support

  • When building Spring REST applications
    • Spring will automatically handle Jackson Integration
    • JSON data being passed to REST controller is converted to POJO
    • Java object being returned from REST controller is converted to JSON

      Set up

      Maven

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      <dependency>
      	<groupId>com.fasterxml.jackson.core</groupId>
      	<artifactId>jackson-databind</artifactId>
      	<version>2.9.5</version>
      </dependency>

Create Student POJO Java Class

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public class Student {

	private int id;
	private String firstName;
	private String lastName;
	private boolean active;
	
	public Student() {
		
	}
	// Getters and Setters	
}

Java POJO to JSON

Basically we are using the method writeValue() of Jackson pacakge.

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ObjectMapper objectMapper = new ObjectMapper();
Student student = new Student();
student.id = 1;
student.firstName = "Xiaoke";
student.lastName = "Liu";
// write in a file
objectMapper.writeValue( new FileOutputStream("data/output-2.json"), student);
// Convert to String
String json = objectMapper.writeValueAsString(student);

JSON to Java POJO

Basically we are using the method readValue() of Jackson pacakge.

  1. Read Object From JSON File

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    public class Driver {

    	public static void main(String[] args) {
    		
    		try {
    			// create object mapper
                // ObjectMapper() from jackson.databind
    			ObjectMapper mapper = new ObjectMapper();
    			
    			// read JSON  file and map/convert to Java POJO: 
    			// data/sample-lite.json
    			Student theStudent = mapper.readValue(
    						new File("data/sample-lite.json"), Student.class);
    			
    			// print first name and last name
    			System.out.println("First name = " + theStudent.getFirstName());
    			System.out.println("Last name = " + theStudent.getLastName());

    		}
    		catch (Exception exc) {
    			exc.printStackTrace();
    		}
    	}
    }

  2. Read Object From JSON Reader

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    ObjectMapper objectMapper = new ObjectMapper();
    String studentJson =  "{ \"id\" : \"001\", \"firstName\" : \"xiaoke\", \"lastName\" : \"Liu\" }";
    Reader reader = new StringReader(carJson);
    Student student = objectMapper.readValue(reader, Student.class);

  3. Read Object From JSON String

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    ObjectMapper objectMapper = new ObjectMapper();
    String studentJson =  "{ \"id\" : \"001\", \"firstName\" : \"xiaoke\", \"lastName\" : \"Liu\" }";
    Student student = objectMapper.readValue(studentJson, Student.class);

  4. Read Object From JSON via URL

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    ObjectMapper objectMapper = new ObjectMapper();
    URL url = new URL("file:data/student.json");
    Student student = objectMapper.readValue(url, Student.class);

If JSON has property you don’t care about, which means that there is no corresponding field in POJO, use@JsonIgnoreProerties(ignoreUnknow=true) over POJO