Java Articles - Page 213 of 745

CrudRepository and JPA repository both are the interface of the spring data repository library. Spring data repository reduces the boilerplate code by providing some predefined finders to access the data layer for various persistence layers. What is JPA repository? JPA is a repository interface that extends CrudRepository and PagingAndSorting repository. It inherits some finders from crud repository such as findOne, gets and removes an entity. It also provides some extra methods related to JPA such as delete records in batch, flushing data directly to a database base and methods related to pagination and sorting. We need to extend this repository ... Read More

The @JsonUnwrapped annotation can be used to unwrap values during the serialization and deserialization process. It helps to render the values of a composed class as if it belongs to the parent class.Syntax@Target(value={ANNOTATION_TYPE, FIELD, METHOD, PARAMETER}) @Retention(value=RUNTIME) public @interface JsonUnwrappedExampleimport com.fasterxml.jackson.annotation.JsonUnwrapped; import com.fasterxml.jackson.databind.ObjectMapper; import com.fasterxml.jackson.core.JsonProcessingException; public class JsonUnwrappedAnnotationTest {    public static void main(String args[]) throws JsonProcessingException {       ObjectMapper mapper = new ObjectMapper();       String jsonString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(new Employee());       System.out.println(jsonString);    } } class Employee {    public int empId = 110;    public String empName = "Raja Ramesh";    @JsonUnwrapped   ... Read More

In Java, Jackson is a library that is used to convert JSON to Java objects and vice versa. Jackson Annotations are used during serialization and deserialization. We use these to denote or specify annotations before a particular field or method (that is declared in Java). Using an annotation before a field, we can denote whether it is a variable, is a JsonProperty, should be ignored, or what condition should be applied to it. So basically, Annotations make JSON output clearer as we required. In this Article, we will learn about ... Read More

The @JSON annotation is used by JSONSerializer class to exclude or include a field during the serialization process. We can use the serialize() method of JSONSerializer class to perform a shallow serialization of the target instance.Syntax@Retention(value=RUNTIME) @Target(value={FIELD, TYPE, METHOD}) public @interface JSONExampleimport flexjson.JSONSerializer; import flexjson.JSON; public class JSONAnnotationTest {    public static void main(String[] args) {       JSONSerializer serializer = new JSONSerializer().prettyPrint(true);       Employee emp = new Employee("Raja", "Ramesh", 30, "Hyderabad");       String jsonStr = serializer.serialize(emp);       System.out.println(jsonStr);    } } // Employee class class Employee {    private String firstName, lastName, address;    private ... Read More

The @JsonDeserialize annotation is used to declare custom deserializer while deserializing JSON to Java object. We can implement a  custom deserializer by extending the StdDeserializer class with a generic type Employee and need to override the deserialize() method of StdDeserializer class.Syntax@Target(value={ANNOTATION_TYPE, METHOD, FIELD, TYPE, PARAMETER}) @Retention(value=RUNTIME) public @interface JsonDeserializeIn the below program, we can implement a custom deserializer using @JsonDeserialize annotationExampleimport java.io.*; import com.fasterxml.jackson.core.*; import com.fasterxml.jackson.databind.*; import com.fasterxml.jackson.databind.annotation.*; import com.fasterxml.jackson.databind.deser.std.*; public class JsonDeSerializeAnnotationTest {    public static void main (String[] args) throws JsonProcessingException, IOException {       Employee emp = new Employee(115, "Adithya");       ObjectMapper mapper = new ObjectMapper();     ... Read More

The @JsonSerialize annotation is used to declare custom serializer during the serialization of a field. We can implement a custom serializer by extending the StdSeralizer class. and need to override the serialize() method of StdSerializer class.Syntax@Target(value={ANNOTATION_TYPE, METHOD, FIELD, TYPE, PARAMETER}) @Retention(value=RUNTIME) public @interface JsonSerializeIn the below program, we can implement a custom serializer using @JsonSerialize annotationExampleimport java.io.*; import com.fasterxml.jackson.core.*; import com.fasterxml.jackson.databind.*; import com.fasterxml.jackson.databind.annotation.*; import com.fasterxml.jackson.databind.ser.std.*; public class JsonSerializeAnnotationTest {    public static void main (String[] args) throws JsonProcessingException, IOException {       Employee emp = new Employee(115, "Adithya", new String[] {"Java", "Python", "Scala"});       ObjectMapper mapper = new ... Read More

The JSON-lib API is a java library to serialize and de-serialize java beans, maps, arrays, and collections in the JSON format. We need to convert a JSON string to a bean by converting a string to JSON object first then convert this to a java bean.Syntaxpublic static Object toBean(JSONObject jsonObject, Class beanClass)In the below program, we can convert a JSON string to a bean.Exampleimport net.sf.json.JSONObject; import net.sf.json.JSONSerializer; public class ConvertJSONStringToBeanTest {    public static void main(String[] args) {       String jsonStr = "{\"firstName\": \"Adithya\", \"lastName\": \"Sai\", \"age\": 30, \"technology\": \"Java\"}";       JSONObject jsonObj = (JSONObject)JSONSerializer.toJSON(jsonStr); // convert String ... Read More

The @JsonIdentityInfo annotation is used when an object has a parent-child relationship in the Jackson library. The @JsonIdentityInfo annotation is used to indicate the object identity during the serialization and deserialization process. The ObjectIdGenerators.PropertyGenerator is an abstract place-holder class to denote a case where Object Identifier to use comes from a POJO property.Syntax@Target(value={ANNOTATION_TYPE, TYPE, FIELD, METHOD, PARAMETER}) @Retention(value=RUNTIME) public @interface JsonIdentityInfoExampleimport java.util.*; import java.io.*; import com.fasterxml.jackson.annotation.JsonIdentityInfo; import com.fasterxml.jackson.annotation.ObjectIdGenerators; import com.fasterxml.jackson.databind.ObjectMapper; public class JsonIdentityInfoTest {    public static void main(String[] args) throws IOException {       ObjectMapper mapper = new ObjectMapper();       User user = new User(115, "Raja", "Ramesh");       ... Read More

The JSONArray is a sequence of values, the external text is a string enclosed in square brackets with commas separating the values and internal text is an object having get() and opt() methods, we need to access those values by index. The element() method for adding or replacing those values. An array is an object that stores multiple values of the same type. It can hold both primitive types and object references. We can convert a JSON array to array by using the toArray() method of JSONArray class. This method produces an Object[] with the contents of JSONArray.Syntaxpublic Object[] toArray()Exampleimport java.util.Arrays; import net.sf.json.JSONArray; public ... Read More

The @Since annotation can use with the setVersion() method of the GsonBuilder class. This annotation can apply to a field in java class and accepts float as an argument. This argument represents the version number in which the field has serialized. The same can apply to the deserialization process.Syntax@Documented @Retention(value=RUNTIME) @Target(value={FIELD, TYPE}) public @interface SinceExampleimport com.google.gson.annotations.Since; import com.google.gson.Gson; import com.google.gson.GsonBuilder; public class GsonSinceAnnotationTest {    public static void main(String[] args) {       Employee emp = new Employee();       emp.setEmployeeName("Raja Ramesh");       emp.setEmployeeId(125);       emp.setEmployeeTechnology("Java");       emp.setEmploeeAddress("Hyderabad");       System.out.println("Since version ... Read More