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Merge pull request #6298 from soufiane-cheouati/master

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Custom annotations files
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Tom Hombergs 2019-02-14 20:12:37 +01:00 committed by GitHub
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13
core-java-8/src/main/java/com/baeldung/customannotations/Init.java Normal file
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package com.baeldung.customannotations;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
@Retention(RUNTIME)
@Target(METHOD)
public @interface Init {
}

13
core-java-8/src/main/java/com/baeldung/customannotations/JsonElement.java Normal file
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package com.baeldung.customannotations;
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
@Retention(RUNTIME)
@Target({ FIELD })
public @interface JsonElement {
public String key() default "";
}

13
core-java-8/src/main/java/com/baeldung/customannotations/JsonSerializable.java Normal file
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package com.baeldung.customannotations;
import static java.lang.annotation.ElementType.TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
@Retention(RUNTIME)
@Target(TYPE)
public @interface JsonSerializable {
}

10
core-java-8/src/main/java/com/baeldung/customannotations/JsonSerializationException.java Normal file
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package com.baeldung.customannotations;
public class JsonSerializationException extends RuntimeException {
private static final long serialVersionUID = 1L;
public JsonSerializationException(String message) {
super(message);
}
}

67
core-java-8/src/main/java/com/baeldung/customannotations/ObjectToJsonConverter.java Normal file
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package com.baeldung.customannotations;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;
import java.util.Objects;
import java.util.stream.Collectors;
public class ObjectToJsonConverter {
public String convertToJson(Object object) throws JsonSerializationException {
try {
checkIfSerializable(object);
initializeObject(object);
return getJsonString(object);
} catch (Exception e) {
throw new JsonSerializationException(e.getMessage());
}
}
private void checkIfSerializable(Object object) {
if (Objects.isNull(object)) {
throw new JsonSerializationException("Can't serialize a null object");
}
Class<?> clazz = object.getClass();
if (!clazz.isAnnotationPresent(JsonSerializable.class)) {
throw new JsonSerializationException("The class " + clazz.getSimpleName() + " is not annotated with JsonSerializable");
}
}
private void initializeObject(Object object) throws IllegalAccessException, IllegalArgumentException, InvocationTargetException {
Class<?> clazz = object.getClass();
for (Method method : clazz.getDeclaredMethods()) {
if (method.isAnnotationPresent(Init.class)) {
method.setAccessible(true);
method.invoke(object);
}
}
}
private String getJsonString(Object object) throws IllegalArgumentException, IllegalAccessException {
Class<?> clazz = object.getClass();
Map<String, String> jsonElementsMap = new HashMap<>();
for (Field field : clazz.getDeclaredFields()) {
field.setAccessible(true);
if (field.isAnnotationPresent(JsonElement.class)) {
jsonElementsMap.put(getKey(field), (String) field.get(object));
}
}
String jsonString = jsonElementsMap.entrySet()
.stream()
.map(entry -> "\"" + entry.getKey() + "\":\"" + entry.getValue() + "\"")
.collect(Collectors.joining(","));
return "{" + jsonString + "}";
}
private String getKey(Field field) {
String value = field.getAnnotation(JsonElement.class)
.key();
return value.isEmpty() ? field.getName() : value;
}
}

66
core-java-8/src/main/java/com/baeldung/customannotations/Person.java Normal file
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package com.baeldung.customannotations;
@JsonSerializable
public class Person {
@JsonElement
private String firstName;
@JsonElement
private String lastName;
@JsonElement(key = "personAge")
private String age;
private String address;
public Person(String firstName, String lastName) {
super();
this.firstName = firstName;
this.lastName = lastName;
}
public Person(String firstName, String lastName, String age) {
this.firstName = firstName;
this.lastName = lastName;
this.age = age;
}
@Init
private void initNames() {
this.firstName = this.firstName.substring(0, 1)
.toUpperCase() + this.firstName.substring(1);
this.lastName = this.lastName.substring(0, 1)
.toUpperCase() + this.lastName.substring(1);
}
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 String getAge() {
return age;
}
public void setAge(String age) {
this.age = age;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
}

26
core-java-8/src/test/java/com/baeldung/customannotations/JsonSerializerUnitTest.java Normal file
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package com.baeldung.customannotations;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertThrows;
import org.junit.jupiter.api.Test;
public class JsonSerializerUnitTest {
@Test
public void givenObjectNotSerializedThenExceptionThrown() throws JsonSerializationException {
Object object = new Object();
ObjectToJsonConverter serializer = new ObjectToJsonConverter();
assertThrows(JsonSerializationException.class, () -> {
serializer.convertToJson(object);
});
}
@Test
public void givenObjectSerializedThenTrueReturned() throws JsonSerializationException {
Person person = new Person("soufiane", "cheouati", "34");
ObjectToJsonConverter serializer = new ObjectToJsonConverter();
String jsonString = serializer.convertToJson(person);
assertEquals("{\"personAge\":\"34\",\"firstName\":\"Soufiane\",\"lastName\":\"Cheouati\"}", jsonString);
}
}