How to format JSON String in Java - Example Tutorial

You can format JSON String in Java using Jackson API's pretty print feature. As you might have noticed in the my previous JSON tutorials that the output of the programs is not properly formatted, which makes them hard to read, especially in large log files where there are so many other text, both JSON and normal text is there. That's why its advised to print JSON String properly formatted because then it will stand out in log file or console. Whenever we print JSON String from Java Programs by using method writeValueAsString(), it usually comes in one line, as shown in following example :

{"name":"Virat","sport":"cricket","age":25,"id":121,"lastScores":[77,72,23,57,54,36,74,17]}

This is not very readable as you cannot see how many attributes are there, what is their name and value, compare it to following formatted output which is printed using Jackson's pretty print feature:

{
  "name" : "Virat",
 "sport" : "cricket",
  "age" : 25,
  "id" : 121,
  "lastScores" : [ 77, 72, 23, 57, 54, 36, 74, 17 ]
}

Its way better than earlier output, its much more readable. You can easily identify which one is just simple name value pair, which one is JSON array and much more. Wondering, how to nicely print JSON String, just checkout the example shown in next section.

Parsing Large JSON Files using Jackson Streaming API Example

In last couple of JSON tutorials for Java programmers, we have learned how to parse JSON using JSON-Simple library, parsing JSON array to Java array using GSon, and in this tutorial we will learn how to parse a large JSON file in Java using Jackson's Streaming API. Jackson is one of the most popular JSON processing framework and provides three main model to parse and process JSON data including Streaming API, data binding and tree model. Out of these three, Streaming works at lowest level and can be used to parse huge JSON response upto even giga bytes of size. If you are familiar with XML parsing, then you know that how difficult it is to parse huge XML files with DOM parser because it fully loads the file in memory before you can process it. In case you have low memory e.g. Android devices you can't use that to parse XML. Thankfully, XML provides SAX and StAX parsers which are streaming based and can be used to process huge files without loading them completely in memory. Out of these two, StAX is even better because it allows pull based processing where client pulls data from parser instead of parser pushing data, which is the case with SAX parser. Jackson's Streaming API is similar to StAX parser. You can pull the data you want and ignore what you don't want. Though performance doesn't come without cost, using Streaming API is little difficult then using other Jackson model which provides direct mapping between Java and Jackson objects. You have to handle all JSON data by yourself while using Streaming API.

How to Read JSON String in Java - Json-Simple Example

JSON is a text format is a widely used as data-interchange language because its parsing and its generation is easy for programs. It is slowly replacing XML as most powerful data interchange format, as it is lightweight, consumes less bandwidth and also platform independent.  Though Java doesn't have built in support for parsing JSON files and objects, there are lot of good open source JSON libraries are available which can help you to read and write JSON object to file and URL. Two of the most popular JSON parsing libraries are Jackson and Gson. They are matured, rich and stable. Though there are couple of more libraries there like JSON simple, which we are going to use in this example. Between Jackson and Gson, later does very nice job in mapping JSON object and serialization. JSON is also used in request and response between client server communication. In this tutorial we are going to see how to read and write JSON to file using JSON.Simple library, and you will notice yourself how simple working with JSON is.

Since we don't have JSON support in JDK, we need to download this open source library. If you are using maven to download JAR and managing dependency, if not then you should, then you can just include following dependencies in your pom.xml file :

    <groupid>com.googlecode.json-simple</groupid>
    <artifactid> json-simple</artifactid>
    <version>1.1</version>

Otherwise, you have to add the newest version of json-simple-1.1.1.jar in CLASSPATH of your Java program. Also, Java 9 is coming up with built in JSON support in JDK, which will make it easier to deal with JSON format, but that will not replace existing Jackson and GSON library, which seems to be very rich with functionality.

How to Convert JSON array to String array in Java - GSon example

JSON array is a ordered collection of values, which are enclosed within brackets e.g. [] and separated by comma. In this Java tutorial we will convert JSON Array to String array in Java and subsequently create JSON from Java String Array. This tutorial is similar to our last article in JSON about How to convert JSON object to Java object, instead of JSON object, here we will convert JSON array to String array or List in Java. As I said earlier, there are lot's of open source library out there which can help to parse JSON data format and we have already seen Jackson library in our last example. In this tutorial we will use GSON to parse JSON data format and create Java String array or List from JSON array representation. Given the popularity of JSON as lightweight alternative of XML to transfer data from Server to client in web applications, it's becoming imperative to know about JSON data format and parsing JSON string, much like parsing XML documents and knowing about different XML parsers e.g. DOM or SAX. Since Java application development is more about reusing existing library, then coding yourself, its important to know what is available, and which library other programmers are using. So far we have seen Jackson library, and here we will explore another one called GSon.

How to convert JSON String to Java object - Jackson Example

JSON, stands for JavaScript object notation, is a light weight text or string representation of object and quickly becoming a popular data exchange format. Though it's pretty early to say that JSON is going to replace XML as popular data interchange format, It is certainly providing an alternative. JSON represent data in two format either an object or an array. JSON object is an unordered collection of key and value, similar to String representation of hashtable. On the other hand JSON Array is an ordered collection of values. Main difference between  JSON Object and  JSON array is there representation. JSON object is started with left brace { and ends with right brace } and key values are separated using colon (:). On the other hand JSON Array starts with left bracket [ and ends with right bracket ] and each value is separated with comma. By looking at structure, You can write  your JSON parser to parse JSON object or array to Java object, but you don't need to. There are lot of open source library in Java which provides tried and tested way of converting JSON String to Java object e.g. Jackson and GSON. In this Java tutorial we will see example of converting a JSON String to Java object using Jackson library