Added demonstration of @JsonFormat and associated test. (#906)

jackson-annotations/src/main/java/com/baeldung/jacksonannotation/format/User.java

@@ -0,0 +1,40 @@
+package com.baeldung.jacksonannotation.format;
+
+import java.util.Date;
+import com.fasterxml.jackson.annotation.JsonFormat;
+
+import com.baeldung.jacksonannotation.domain.Person;
+
+/**
+ * @author Jay Sridhar
+ * @version 1.0
+ */
+public class User extends Person {
+    private String firstName;
+    private String lastName;
+
+    @JsonFormat(shape = JsonFormat.Shape.STRING,
+		pattern = "yyyy-MM-dd@HH:mm:ss.SSSZ")
+    private Date createdDate;
+
+    public User(String firstName,String lastName) {
+	super(firstName, lastName);
+	this.createdDate = new Date();
+    }
+
+    public Date getCreatedDate() {
+        return createdDate;
+    }
+
+    @JsonFormat(shape = JsonFormat.Shape.STRING,
+		pattern = "yyyy-MM-dd@HH:mm:ss.SSSZ",
+		locale = "en_GB")
+    public Date getCurrentDate() {
+	return new Date();
+    }
+
+    @JsonFormat(shape = JsonFormat.Shape.NUMBER)
+    public Date getDateNum() {
+	return new Date();
+    }
+}

jackson-annotations/src/test/java/com/baeldung/jacksonannotation/format/JsonFormatTest.java

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+package com.baeldung.jacksonannotation.format;
+
+import java.util.Date;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+import org.junit.Test;
+
+import static io.restassured.path.json.JsonPath.from;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.data.Percentage.withPercentage;
+
+/**
+ * @author Jay Sridhar
+ * @version 1.0
+ */
+public class JsonFormatTest {
+
+    @Test
+    public void whenSerializedDateFormat_thenCorrect() throws JsonProcessingException {
+
+	User user = new User("Jay", "Sridhar");
+
+	String result = new ObjectMapper().writeValueAsString(user);
+
+	// Expected to match: "2016-12-19@09:34:42.628+0000"
+	assertThat(from(result).getString("createdDate"))
+	    .matches("\\d{4}\\-\\d{2}\\-\\d{2}@\\d{2}:\\d{2}:\\d{2}\\.\\d{3}\\+\\d{4}");
+
+	// Expected to be close to current time
+	long now = new Date().getTime();
+	assertThat(from(result).getLong("dateNum"))
+	    .isCloseTo(now, withPercentage(10.0));
+
+    }
+}