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How to Serialize Java.util.Date with Jackson JSON Processor / Spring 3.0

09.20.2010
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Quick tip: how to serialize a java.util.Date object with Jackson JSON Processor – Spring MVC 3.

package com.loiane.model;

import java.util.Date;

import org.codehaus.jackson.annotate.JsonAutoDetect;

@JsonAutoDetect
@Entity
public class Company {

	private int id;
	private double price;
	private String company;
	private Date date;
	private String size;
	private byte visible;
}

And I have the following method in my controller:

public @ResponseBody Map<String,List<Company>> view() throws Exception

Which returns a list of Company.

The @ResponseBody annotation instructs Spring MVC to serialize the hashmap to the client. Spring MVC automatically serializes to JSON because the client accepts that content type:

{"total":27,"data":[{"price":71.72,"company":"3m Co","visible":1,"id":1,"size":"large","date":1188615600000},{"price":29.01,"company":"Aloca
Inc","visible":0,"id":2,"size":"medium","date":1185937200000},{"price":83.81,"company":"Altria Group
Inc","visible":0,"id":3,"size":"large","date":1186110000000},{"price":52.55,"company":"American Express Company","visible":1,"id":4,"size":"extra
large","date":1199412000000},{"price":64.13,"company":"American International Group
Inc.","visible":1,"id":5,"size":"small","date":1204599600000},{"price":31.61,"company":"AT&T Inc.","visible":0,"id":6,"size":"extra
large","date":1201831200000},{"price":75.43,"company":"Boeing Co.","visible":1,"id":7,"size":"large","date":1199152800000},{"price":67.27,"company":"Caterpillar
Inc.","visible":1,"id":8,"size":"medium","date":1196647200000},{"price":49.37,"company":"Citigroup,
Inc.","visible":1,"id":9,"size":"large","date":1195869600000},{"price":40.48,"company":"E.I. du Pont de Nemours and Company","visible":0,"id":10,"size":"extra
large","date":1178679600000}],"success":true}

Take a look how the date attibute is being serialized: “date”:1188615600000. Jackson uses default strategy to determine date formatting in serialization.

One of the annotations Jackson has is @JsonSerialize. You basically use this annotation for configuring serialization aspects. In my case, I decorated by model objects date getter method with this annotation:

@JsonSerialize(using=JsonDateSerializer.class)
public Date getDate() {
	return date;
}

JsonDateSerializer is a class I wrote that extends JsonSerializer that will handle the serialization for this field:

 

package com.loiane.util;

import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;

import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.JsonProcessingException;
import org.codehaus.jackson.map.JsonSerializer;
import org.codehaus.jackson.map.SerializerProvider;
import org.springframework.stereotype.Component;

/**
 * Used to serialize Java.util.Date, which is not a common JSON
 * type, so we have to create a custom serialize method;.
 *
 * @author Loiane Groner
 * http://loianegroner.com (English)
 * http://loiane.com (Portuguese)
 */
@Component
public class JsonDateSerializer extends JsonSerializer<Date>{

	private static final SimpleDateFormat dateFormat = new SimpleDateFormat("MM-dd-yyyy");

	@Override
	public void serialize(Date date, JsonGenerator gen, SerializerProvider provider)
			throws IOException, JsonProcessingException {

		String formattedDate = dateFormat.format(date);

		gen.writeString(formattedDate);
	}

}

And this is how my object is being serialized now:

{"total":27,"data":[{"price":71.72,"company":"3m Co","visible":1,"id":1,"size":"large","date":"09-01-2007"},{"price":29.01,"company":"Aloca
Inc","visible":0,"id":2,"size":"medium","date":"08-01-2007"},{"price":83.81,"company":"Altria Group
Inc","visible":0,"id":3,"size":"large","date":"08-03-2007"},{"price":52.55,"company":"American Express Company","visible":1,"id":4,"size":"extra
large","date":"01-04-2008"},{"price":64.13,"company":"American International Group
Inc.","visible":1,"id":5,"size":"small","date":"03-04-2008"},{"price":31.61,"company":"AT&T Inc.","visible":0,"id":6,"size":"extra
large","date":"02-01-2008"},{"price":75.43,"company":"Boeing Co.","visible":1,"id":7,"size":"large","date":"01-01-2008"},{"price":67.27,"company":"Caterpillar
Inc.","visible":1,"id":8,"size":"medium","date":"12-03-2007"},{"price":49.37,"company":"Citigroup,
Inc.","visible":1,"id":9,"size":"large","date":"11-24-2007"},{"price":40.48,"company":"E.I. du Pont de Nemours and Company","visible":0,"id":10,"size":"extra
large","date":"05-09-2007"}],"success":true}

Happy coding!

From http://loianegroner.com/2010/09/how-to-serialize-java-util-date-with-jackson-json-processor-spring-3-0/

Published at DZone with permission of Loiane Groner, author and DZone MVB.

(Note: Opinions expressed in this article and its replies are the opinions of their respective authors and not those of DZone, Inc.)

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Comments

Xavier Dury replied on Mon, 2010/09/20 - 3:13am

Using a static date format without synchronization is not recommended.
Excerpt from SimpleDateFormat javadoc:

Date formats are not synchronized. It is recommended to create separate format instances for each thread. If multiple threads access a format concurrently, it must be synchronized externally.

Aries McRae replied on Mon, 2010/09/20 - 6:09am

The Apache FastDateFormat is a thread-safe version of SimpleDateFormat.
It doesn't parse, but it can be used for formatting.

John Cook replied on Mon, 2010/09/20 - 10:12am

I recently decided to ditch using SimpleDateFormat altogether because thinking about thread safety when you don't have to sucks.  As mentioned, use FastDateFormat.  Or use the Joda Time API.

Here's a shameless link to my blog about date formatting:

http://programmerjohncook.blogspot.com/2010/08/simpledateformat-will-harm-your-pets.html

Javin Paul replied on Sat, 2011/04/16 - 9:22am

Nice article , you have indeed covered topic in details and code example.

Thanks
Javin
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