General Annotations in Jackson

General annotations include several basic annotations which we use in serialization and deserialization. JsonProperty and JsonView are the two generally used annotations at the time of serialization and deserialization.

Let’s understand each one of them in detail with an example:

@JsonProperty

It is an important general annotation that we used for marking the non-standard getter/setter method, i.e., to be used with respect to Json Property. Let’s take an example to understand how it works:

JsonPropertyExample.java

  // import required classes and package  import java.io.IOException;  import com.fasterxml.jackson.annotation.JsonProperty;  import com.fasterxml.jackson.databind.ObjectMapper;    // create class JsonPropertyExample to understand how it works   public class JsonPropertyExample {            // main() method start      public static void main(String args[]) throws IOException {                    // create an instance of ObjectMapper class          ObjectMapper mapper = new ObjectMapper();                    String json = “{“name”:”Sharon”,”id”:101, “course”:”MCA”}”;                    // de-serializing Json into Java object          Student std = mapper.readerFor(Student.class).readValue(json);                    // print id, name and course of student          System.out.println(std.getStdId());          System.out.println(std.getStdName());          System.out.println(std.getCourse());      }  }  class Student {      private int id;      private String name;      private String course;            // default constructor      Student(){                }      // parameterized constructor       Student(int id, String name, String course){          this.id = id;          this.name = name;          this.course = course;      }      @JsonProperty(“”)      public int getStdId() {          return id;      }      @JsonProperty(“id”)      public void setStdId(int id) {          this.id = id;      }      @JsonProperty(“name”)      public String getStdName() {          return name;      }      @JsonProperty(“name”)      public void setStdName(String name) {          this.name = name;      }        @JsonProperty(“course”)      public String getCourse() {          return course;      }      @JsonProperty(“course”)      public void setCourse(String course) {          this.course = course;      }    }  

Output:

General Annotations in Jackson

@JsonFormat

It is another important annotation that is used for specifying the format at the time of serialization and deserialization. It is mostly used for specifying date format.

Let’s take an example to understand how annotation is used for specifying a format for the date field.

JsonFormatExample.java

  //import required classes and package    import java.io.IOException;  import java.text.ParseException;  import java.text.SimpleDateFormat;  import java.util.Date;  import java.util.Scanner;    import com.fasterxml.jackson.annotation.JsonFormat;  import com.fasterxml.jackson.annotation.JsonProperty;  import com.fasterxml.jackson.databind.ObjectMapper;    //create class JsonFormatExample to understand how it works   public class JsonFormatExample {            // main() method start      public static void main(String args[]) throws IOException, ParseException  {                    // create an instance of ObjectMapper class          ObjectMapper mapper = new ObjectMapper();                    // create Scanner class object          Scanner sc= new Scanner(System.in);                    try{                            Student std = new Student();                            String stdId, stdName, stdCourse, stdAddmission;                            System.out.println(“Enter Student Id:”);              stdId = sc.nextLine();              std.setStdId(stdId);                            System.out.println(“Enter Student Name:”);              stdName = sc.nextLine();              std.setStdName(stdName);                            System.out.println(“Enter Course Name:”);              stdCourse = sc.nextLine();              std.setCourse(stdCourse);                            System.out.println(“Enter Addmission Date(dd-MM-yyyy):”);              stdAddmission = sc.nextLine();                            SimpleDateFormat sdf = new SimpleDateFormat(“dd-MM-yyyy”);              Date date = sdf.parse(stdAddmission);              std.setAddmission(date);                            // convert Java type into Json string              String jsonString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(std);               System.out.println(jsonString);           }           catch (IOException e) {               e.printStackTrace();           }                    // close Scanner class object          sc.close();      }  }  class Student {      private String id;      private String name;      public String course;      @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = “dd-MM-yyyy”)      public Date addmission;            // getter and setter      @JsonProperty(“id”)      public String getStdId() {          return id;      }      @JsonProperty(“id”)      public void setStdId(String id) {          this.id = id;      }      @JsonProperty(“name”)      public String getStdName() {          return name;      }      @JsonProperty(“name”)      public void setStdName(String name) {          this.name = name;      }        public String getCourse() {          return course;      }      public void setCourse(String course) {          this.course = course;      }      public Date getAddmission() {          return addmission;      }      public void setAddmission(Date addmission) {          this.addmission = addmission;      }   }  

Output:

General Annotations in Jackson

@JsonUnwrapped

It is another important annotation that comes in general annotations. It is used for unwrapping an object’s values at the time or serialization and deserialization.

Let’s take an example to understand how the annotation is used for wrapping the values.

JsonUnwrapperdExample.java

  //import required classes and package  import java.io.IOException;  import java.text.ParseException;  import java.text.SimpleDateFormat;  import java.util.Date;  import java.util.Scanner;    import com.fasterxml.jackson.annotation.JsonFormat;  import com.fasterxml.jackson.annotation.JsonProperty;  import com.fasterxml.jackson.annotation.JsonUnwrapped;  import com.fasterxml.jackson.databind.ObjectMapper;    //create class JsonUnwrapperdExample to understand the working of it  public class JsonUnwrapperdExample {            // main() method start      public static void main(String args[]) throws IOException, ParseException  {                    // create an instance of ObjectMapper class          ObjectMapper mapper = new ObjectMapper();                    // create Scanner class object          Scanner sc= new Scanner(System.in);                    try{                            Student std = new Student();                            String stdId, firstName, lastName, stdCourse, stdAddmission;                            System.out.println(“Enter Student Id:”);              stdId = sc.nextLine();              std.setStdId(stdId);                            System.out.println(“Enter First Name:”);              firstName = sc.nextLine();                            System.out.println(“Enter Last Name:”);              lastName = sc.nextLine();                            std.setStdName(new Student.Name(firstName, lastName));                            System.out.println(“Enter Course Name:”);              stdCourse = sc.nextLine();              std.setCourse(stdCourse);                            System.out.println(“Enter Addmission Date(dd-MM-yyyy):”);              stdAddmission = sc.nextLine();                            SimpleDateFormat sdf = new SimpleDateFormat(“dd-MM-yyyy”);              Date date = sdf.parse(stdAddmission);              std.setAddmission(date);                            // convert Java type into Json string              String jsonString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(std);               System.out.println(jsonString);           }           catch (IOException e) {               e.printStackTrace();           }                    // close Scanner class object          sc.close();      }  }  class Student {      private String id;      @JsonUnwrapped      public Name name;      public String course;      @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = “dd-MM-yyyy”)      public Date addmission;            // getter and setter      @JsonProperty(“id”)      public String getStdId() {          return id;      }      @JsonProperty(“id”)      public void setStdId(String id) {          this.id = id;      }      @JsonProperty(“name”)      public Name getStdName() {          return name;      }      @JsonProperty(“name”)      public void setStdName(Name name) {          this.name = name;      }        public String getCourse() {          return course;      }      public void setCourse(String course) {          this.course = course;      }      public Date getAddmission() {          return addmission;      }      public void setAddmission(Date addmission) {          this.addmission = addmission;      }       static class Name {          public String firstName;          public String lastName;                    // parameterized constructor          public Name(String firstName, String lastName) {              this.firstName = firstName;              this.lastName = lastName;          }      }  }  

Output:

General Annotations in Jackson

@JsonUnwrapped

It is another important annotation that is used for controlling values to be serialized or not. Let’s take an example to understand how the annotation is used for controlling the values.

JsonViewExample.java

  //import required classes and package  import java.io.IOException;  import java.text.ParseException;  import java.text.SimpleDateFormat;  import java.util.Date;  import java.util.Scanner;    import com.fasterxml.jackson.annotation.JsonFormat;  import com.fasterxml.jackson.annotation.JsonProperty;  import com.fasterxml.jackson.annotation.JsonView;  import com.fasterxml.jackson.databind.ObjectMapper;    //create class JsonViewExample to understand how it works   public class JsonViewExample {            // main() method start      public static void main(String args[]) throws IOException, ParseException  {                    // create an instance of ObjectMapper class          ObjectMapper mapper = new ObjectMapper();                    // create Scanner class object          Scanner sc= new Scanner(System.in);                    try{                            Student std = new Student();                            String stdId, stdName, stdCourse, stdAddmission;                            System.out.println(“Enter Student Id:”);              stdId = sc.nextLine();              std.setStdId(stdId);                            System.out.println(“Enter Student Name:”);              stdName = sc.nextLine();              std.setStdName(stdName);                            System.out.println(“Enter Course Name:”);              stdCourse = sc.nextLine();              std.setCourse(stdCourse);                            System.out.println(“Enter Addmission Date(dd-MM-yyyy):”);              stdAddmission = sc.nextLine();                            SimpleDateFormat sdf = new SimpleDateFormat(“dd-MM-yyyy”);              Date date = sdf.parse(stdAddmission);              std.setAddmission(date);                            // convert Java type into Json string              String jsonString = mapper.writerWithDefaultPrettyPrinter().withView(Views.Public.class).writeValueAsString(std);               System.out.println(jsonString);           }           catch (IOException e) {               e.printStackTrace();           }                    // close Scanner class object          sc.close();      }  }  class Student {      @JsonView(Views.Public.class)      private String id;      @JsonView(Views.Public.class)      private String name;      @JsonView(Views.Internal.class)      public String course;      @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = “dd-MM-yyyy”)@JsonView(Views.Public.class)      public Date addmission;            // getter and setter      @JsonProperty(“id”)      public String getStdId() {          return id;      }      @JsonProperty(“id”)      public void setStdId(String id) {          this.id = id;      }      @JsonProperty(“name”)      public String getStdName() {          return name;      }      @JsonProperty(“name”)      public void setStdName(String name) {          this.name = name;      }        public String getCourse() {          return course;      }      public void setCourse(String course) {          this.course = course;      }      public Date getAddmission() {          return addmission;      }      public void setAddmission(Date addmission) {          this.addmission = addmission;      }   }  class Views {            static class Public {                }      static class Internal extends Public {                }  }  

Output:

General Annotations in Jackson

@JsonManagedReferences/@JsonBackReferences

@JsonManagedReference and @JsonBackReferences are the two important annotations that are used for displaying the relationship with the parent-child relationship.

@JsonManagedReference is used for referring to parent objects whereas @JsonBackReferences is used for marking child objects.

Let’s take an example to understand how both annotations are used for displaying relationship between objects.

JsonReferenceExample.java

  //import required classes and package  import java.io.IOException;  import java.text.ParseException;  import java.util.ArrayList;  import java.util.List;  import java.util.Scanner;    import com.fasterxml.jackson.annotation.JsonBackReference;  import com.fasterxml.jackson.annotation.JsonManagedReference;  import com.fasterxml.jackson.annotation.JsonProperty;  import com.fasterxml.jackson.databind.ObjectMapper;    //create class JsonReferenceExample to understand how it works   public class JsonReferenceExample {            // main() method start      public static void main(String args[]) throws IOException, ParseException  {                    // create an instance of ObjectMapper class          ObjectMapper mapper = new ObjectMapper();                    // create Scanner class object          Scanner sc= new Scanner(System.in);                    try{                            Student std = new Student();                            String stdId, stdName, stdCourse;                            System.out.println(“Enter Student Id:”);              stdId = sc.nextLine();              std.setStdId(stdId);                            System.out.println(“Enter Student Name:”);              stdName = sc.nextLine();              std.setStdName(stdName);                            System.out.println(“Enter Course Name:”);              stdCourse = sc.nextLine();              std.setCourse(stdCourse);                            Book obj1 = new Book(121,”Learn C Programming”, std);              Book obj2 = new Book(131,”Learn Advance Java”, std);                            std.addBook(obj1);              std.addBook(obj2);                            // convert Java type into Json string              String jsonString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(obj1);               System.out.println(jsonString);           }           catch (IOException e) {               e.printStackTrace();           }                    // close Scanner class object          sc.close();      }  }  class Student {      private String id;      private String name;      public String course;            @JsonBackReference      public List books;            // default constructor      public Student() {          this.books = new ArrayList();      }      // getter and setter      @JsonProperty(“id”)      public String getStdId() {          return id;      }      @JsonProperty(“id”)      public void setStdId(String id) {          this.id = id;      }      @JsonProperty(“name”)      public String getStdName() {          return name;      }      @JsonProperty(“name”)      public void setStdName(String name) {          this.name = name;      }        public String getCourse() {          return course;      }      public void setCourse(String course) {          this.course = course;      }      public void addBook(Book book){          books.add(book);      }  }  class Book {      public int bookId;      public String bookName;            Book(int bookId, String bookName, Student bookOwner){          this.bookId = bookId;          this.bookName = bookName;          this.bookOwner = bookOwner;      }      @JsonManagedReference      public Student bookOwner;  }  

Output:

General Annotations in Jackson

@JsonIdentityInfo

When objects have a parent-child relationship, @JsonIdentityInfo is used for indicating that object identity will be used during serialization/deserialization.

Let’s take an example to understand the working of @JsonIdentityInfo annotation.

JsonIdentityInfoExample.java

  //import required classes and package  import java.io.IOException;  import java.text.ParseException;  import java.util.ArrayList;  import java.util.List;  import java.util.Scanner;    import com.fasterxml.jackson.annotation.JsonIdentityInfo;  import com.fasterxml.jackson.annotation.JsonProperty;  import com.fasterxml.jackson.annotation.ObjectIdGenerators;  import com.fasterxml.jackson.databind.ObjectMapper;    //create class JsonIdentityInfoExample to understand how it works   public class JsonIdentityInfoExample {            // main() method start      public static void main(String args[]) throws IOException, ParseException  {                    // create an instance of ObjectMapper class          ObjectMapper mapper = new ObjectMapper();                    // create Scanner class object          Scanner sc= new Scanner(System.in);                    try{                            Student std = new Student();                            String stdId, stdName, stdCourse;                            System.out.println(“Enter Student Id:”);              stdId = sc.nextLine();              std.setStdId(stdId);                            System.out.println(“Enter Student Name:”);              stdName = sc.nextLine();              std.setStdName(stdName);                            System.out.println(“Enter Course Name:”);              stdCourse = sc.nextLine();              std.setCourse(stdCourse);                            Book obj1 = new Book(121,”Learn C Programming”, std);              Book obj2 = new Book(131,”Learn Advance Java”, std);                            std.addBook(obj1);              std.addBook(obj2);                            // convert Java type into Json string              String jsonString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(obj1);               System.out.println(jsonString);           }           catch (IOException e) {               e.printStackTrace();           }                    // close Scanner class object          sc.close();      }  }  @JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = “id”)  class Student {      private String id;      private String name;      public String course;      public List books;            // default constructor      public Student() {          this.books = new ArrayList();      }      // getter and setter      @JsonProperty(“id”)      public String getStdId() {          return id;      }      @JsonProperty(“id”)      public void setStdId(String id) {          this.id = id;      }      @JsonProperty(“name”)      public String getStdName() {          return name;      }      @JsonProperty(“name”)      public void setStdName(String name) {          this.name = name;      }        public String getCourse() {          return course;      }      public void setCourse(String course) {          this.course = course;      }      public void addBook(Book book){          books.add(book);      }  }  @JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = “bookId”)  class Book {      public int bookId;      public String bookName;      public Student bookOwner;            Book(int bookId, String bookName, Student bookOwner){          this.bookId = bookId;          this.bookName = bookName;          this.bookOwner = bookOwner;      }  }  

Output:

General Annotations in Jackson

@JsonFilter

@JsonFilter is another useful annotation that we used for applying filters at the time of serialization/deserialization.

Let’s take an example to understand how we can apply filters by using @JsonFilter.

JsonFilterExample.java

  //import required classes and package if any  import java.io.IOException;  import java.util.Scanner;    import com.fasterxml.jackson.annotation.JsonFilter;  import com.fasterxml.jackson.databind.ObjectMapper;  import com.fasterxml.jackson.databind.ser.FilterProvider;  import com.fasterxml.jackson.databind.ser.impl.SimpleBeanPropertyFilter;  import com.fasterxml.jackson.databind.ser.impl.SimpleFilterProvider;    //create class JsonFilterExample to understand the working of annotation  public class JsonFilterExample {            //main() methods start      public static void main(String args[]) {                    // create an instance of ObjectMapper class          ObjectMapper mapper = new ObjectMapper();                    // create Scanner class object          Scanner sc= new Scanner(System.in);                    // using try-catch for serializing Product          try {                            Product product;                            String proId, proName, proPrice, proExpiry;                            System.out.println(“Enter Product Id:”);              proId = sc.nextLine();                            System.out.println(“Enter Product Name”);              proName = sc.nextLine();                            System.out.println(“Enter Product Price”);              proPrice = sc.nextLine();                            System.out.println(“Enter Product Expiry in dd-mm-yyyy format”);              proExpiry = sc.nextLine();                            // set values to Student object by using constructor              product = new Product(proId, proName, proPrice, proExpiry);                               FilterProvider filters = new SimpleFilterProvider() .addFilter(                  “nameFilter”, SimpleBeanPropertyFilter.filterOutAllExcept(“name”));                            // serialize Product using mapper              String jsonString = mapper                  .writer(filters)                  .withDefaultPrettyPrinter()                  .writeValueAsString(product);              System.out.println(jsonString);          }          catch (IOException e) {               e.printStackTrace();          }                    //close Scanner class object          sc.close();                }  }  //create class Product by using @JsonFilter  @JsonFilter(“nameFilter”)  class Product {              //Creating properties of Product class        public String proId;          public String name;          public String price;      public String expire;             // constructor      Product(String proId, String name, String price, String expire){          this.proId = proId;          this.name = name;          this.price = price;          this.expire = expire;      }  }  

Output:

General Annotations in Jackson

Next TopicMiscellaneous Annotations in Jackson

General Annotations in Jackson

General Annotations in Jackson

@JsonProperty

@JsonFormat

@JsonUnwrapped

@JsonUnwrapped

@JsonManagedReferences/@JsonBackReferences

@JsonIdentityInfo

@JsonFilter

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