{"id":8487,"date":"2014-01-24T15:45:52","date_gmt":"2014-01-24T13:45:52","guid":{"rendered":"http:\/\/examples.javacodegeeks.com\/?p=8487"},"modified":"2021-09-24T13:21:04","modified_gmt":"2021-09-24T10:21:04","slug":"java-json-parser-example","status":"publish","type":"post","link":"https:\/\/examples.javacodegeeks.com\/java-json-parser-example\/","title":{"rendered":"Java JSON parser Example"},"content":{"rendered":"

In this post, we feature a comprehensive Java JSON parser Example. JSON<\/code> is simply a text format that facilitates reading and writing. It is a widely used data-interchange language because of its parsing and its generation is easy for machines. In Java language, there are many ways for JSON<\/code> processing.<\/p>\n

1. JSON Parsers<\/h2>\n

In this section, we will see four different parsers for JSON<\/code> available in the Java ecosystem.<\/p>\n

1.1. Simple JSON parser<\/h3>\n

In this section we are going to use a common Java toolkit for JSON<\/code> – JSON.simple<\/code><\/a>. Before start coding we have to set a proper environment for the compiler to recognize the JSON's<\/code> classes. If you want to build your project via Maven, you should add the following dependency to your pom.xml<\/code>:<\/p>\n

pom.xml<\/em><\/span><\/p>\n

<dependency>\n    <groupId>com.googlecode.json-simple<\/groupId>\n    <artifactId>json-simple<\/artifactId>\n    <version>1.1<\/version>\n<\/dependency>\n<\/pre>\n
As we mentioned, we will show how we can parse a JSON file, so we will make our own .json<\/code> file. The file should be placed in src\/main\/resources<\/code> directory. This file is named jsonTestFile.json<\/code> and has the following structure:<\/p>\n
jsonTestFile.json<\/em><\/span><\/p>\n
{\n  \"id\": 1,\n  \"firstname\": \"Katerina\",\n  \"languages\": [\n    {\n      \"lang\": \"en\",\n      \"knowledge\": \"proficient\"\n    },\n    {\n      \"lang\": \"fr\",\n      \"knowledge\": \"advanced\"\n    }\n  ],\n  \"job\": {\n    \"site\": \"www.javacodegeeks.com\",\n    \"name\": \"Java Code Geeks\"\n  }\n}\n<\/pre>\n
Now create a java file in your project, named JsonParseTest<\/code>. Then paste the following code.<\/p>\n
JsonParseTest.java<\/em><\/span><\/p>\n
package com.javacodegeeks.javabasics.jsonparsertest;\n \nimport java.io.FileNotFoundException;\nimport java.io.FileReader;\nimport java.io.IOException;\nimport java.util.Iterator;\n \nimport org.json.simple.JSONArray;\nimport org.json.simple.JSONObject;\nimport org.json.simple.parser.JSONParser;\nimport org.json.simple.parser.ParseException;\n \npublic class JsonParseTest {\n \n    private static final String filePath = \"jsonTestFile.json\";\n\n    public static void main(String[] args) {\n\n        try (FileReader reader = new FileReader(ClassLoader.getSystemResource(filePath).getFile())) {\n            \/\/ read the json file\n\n\n            JSONParser jsonParser = new JSONParser();\n            JSONObject jsonObject = (JSONObject) jsonParser.parse(reader);\n\n            \/\/ get a String from the JSON object\n            String firstName = (String) jsonObject.get(\"firstname\");\n            System.out.println(\"The first name is: \" + firstName);\n\n            \/\/ get a number from the JSON object\n            long id = (long) jsonObject.get(\"id\");\n            System.out.println(\"The id is: \" + id);\n\n            \/\/ get an array from the JSON object\n            JSONArray lang = (JSONArray) jsonObject.get(\"languages\");\n\n            \/\/ take the elements of the json array\n            for (int i = 0; i < lang.size(); i++) {\n                System.out.println(\"The \" + i + \" element of the array: \" + lang.get(i));\n            }\n            Iterator i = lang.iterator();\n\n            \/\/ take each value from the json array separately\n            while (i.hasNext()) {\n                JSONObject innerObj = (JSONObject) i.next();\n                System.out.println(\"language \" + innerObj.get(\"lang\") +\n                        \" with level \" + innerObj.get(\"knowledge\"));\n            }\n            \/\/ handle a structure into the json object\n            JSONObject structure = (JSONObject) jsonObject.get(\"job\");\n            System.out.println(\"Into job structure, name: \" + structure.get(\"name\"));\n\n        } catch (Exception ex) {\n            ex.printStackTrace();\n        }\n    }\n \n}\n<\/pre>\n
Now let’s explain the code above. After we create an instance of JSONParser<\/code>, we create a JSONObject<\/code> by parsing the FileReader<\/code> of our .json<\/code> file. This JSONObject<\/code> contains a collection of key-value pairs, from which we can get every value of the JSON file. To retrieve primitive objects, get()<\/code> method of the JSONObject's<\/code> instance is called, defining the specified key as an argument. It is important to add the suitable cast to the method. For array types in JSON file, JSONArray<\/code> is used that represents an ordered sequence of values. As you can notice in the code, an Iterator<\/code> should be used in order to take each value of the JSON array. A structure in the JSON file, signs the creation of a new JSONObject<\/code> in order to retrieve the values.
 
<\/div> <\/div><\/p>\n
You can see the output of the execution below.<\/p>\n
Output:<\/em><\/span><\/p>\n
The first name is: Katerina\nThe id is: 1\nThe 0 element of the array: {\"knowledge\":\"proficient\",\"lang\":\"en\"}\nThe 1 element of the array: {\"knowledge\":\"advanced\",\"lang\":\"fr\"}\nlanguage en with level proficient\nlanguage fr with level advanced\nInto job structure, name: Java Code Geeks\n<\/pre>\n
1.2. GSON parser<\/h3>\n
In this section, We will cover the Gson<\/code> library to convert JSON to object and vice versa. Gson can work with arbitrary Java objects including preexisting objects. It also supports the use of Java Generics. <\/p>\n
pom.xml<\/em><\/span><\/p>\n
<dependency>\n    <groupId>com.google.code.gson<\/groupId>\n    <artifactId>gson<\/artifactId>\n    <version>2.8.6<\/version>\n<\/dependency>\n<\/pre>\n
This adds the Gson<\/code> dependency to our project so that we can use it deserialize the JSON into java object.<\/p>\n
GsonParseTest.java<\/em><\/span><\/p>\n
public class GsonParseTest {\n\n    private static final String filePath = \"jsonTestFile.json\";\n\n    public static void main(String[] args) {\n        Gson gson = new Gson();\n        try (FileReader reader = new FileReader(ClassLoader.getSystemResource(filePath).getFile())) {\n            Person person = gson.fromJson(reader, Person.class);\n            System.out.println(person.toString());\n       } catch (Exception ex) {\n            ex.printStackTrace();\n       }\n   }\n}<\/pre>\n