Table of Contents
In this post,we will see how can we will use jackson streaming API to read and write JSON .
Java JSON Tutorial Content:
- JSON Introduction
- JSON.simple example-read and write JSON
- GSON example-read and write
- JSONJackson example – read and write JSON
- Jackson Streaming API – read and write JSON
In previous post, we have seen jackson example, but it reads whole json file in memory but if we have large json file, then it is not efficient. So If you want to read or write large json file, we need to use jackson streaming API which do not read whole file in memory.
Two important classes for jackson streaming API are:
- JsonGenerator : To write json
- JsonParser : To read json
But Jackson streaming API is very less flexible and can not be easily used. We need to handle each and every field and there is no need to create java object unless explicitly required.
In this post,we will read and write JSON using Jackson Streaming API.
1). Create a java project named “JacksonStreamingAPIExample”
2)Â Add following maven dependency for jackson.
Pom.xml :
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.arpit.java2blog</groupId> <artifactId>JacksonStreamingAPIExample</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>jar</packaging> <name>JacksonStreamingAPIExample</name> <url>http://maven.apache.org</url> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> </properties> <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>3.8.1</version> <scope>test</scope> </dependency> <dependency> <groupId>org.codehaus.jackson</groupId> <artifactId>jackson-xc</artifactId> <version>1.9.13</version> </dependency> </dependencies> </project> |
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package org.arpit.java2blog.pojo; import java.util.ArrayList; import java.util.List; public class Country { String name; int population; private List listOfStates; //getter and setter methods public String getName() { return name; public void setName(String name) { this.name = name; } public int getPopulation() { return population; } public void setPopulation(int population) { this.population = population; } public List getListOfStates() { return listOfStates; } public void setListOfStates(List listOfStates) { this.listOfStates = listOfStates; } } |
Write JSON to file:
4) Create a new class named “JacksonWriteToFileStreamingAPIExample.java” in src->org.arpit.java2blog.JacksonStreamingAPIExample
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package com.arpit.java2blog.JacksonStreamingAPIExample; import java.io.File; import java.io.IOException; import org.codehaus.jackson.JsonEncoding; import org.codehaus.jackson.JsonFactory; import org.codehaus.jackson.JsonGenerationException; import org.codehaus.jackson.JsonGenerator; import org.codehaus.jackson.util.DefaultPrettyPrinter; /** * * @author Arpit Mandliya * */ public class JacksonWriteToFileStreamingAPIExample { public static void main( String[] args ) { try { JsonFactory jfactory = new JsonFactory(); // Write json to a file JsonGenerator jsonGenerator = jfactory.createJsonGenerator(new File("//Users//Arpit//countryStreaming.json"), JsonEncoding.UTF8); jsonGenerator.setPrettyPrinter(new DefaultPrettyPrinter()); jsonGenerator.writeStartObject(); // { //"name" : "India" jsonGenerator.writeStringField("name", "India"); // "population" : "10000" jsonGenerator.writeNumberField("population", 10000); // "listOfStates" : // This is an array object jsonGenerator.writeFieldName("listOfStates"); // Create start of array tag [ jsonGenerator.writeStartArray(); jsonGenerator.writeString("Madhya Pradesh"); jsonGenerator.writeString("Maharashtra"); jsonGenerator.writeString("Rajasthan"); // Create End of array tag ] jsonGenerator.writeEndArray(); // end of JSON Object tag } jsonGenerator.writeEndObject(); jsonGenerator.close(); } catch (JsonGenerationException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } } |
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{ "name" : "India", "population" : 10000, "listOfStates" : [ "Madhya Pradesh", "Maharashtra", "Rajasthan" ] } |
Read JSON to file:
Here we will read above created JSON file.
5) Create a new class named “JacksonJsonReadFromFileExample.java” in src->org.arpit.java2blog.JacksonStreamingAPIExample
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package com.arpit.java2blog.JacksonStreamingAPIExample; import java.io.File; import java.io.IOException; import org.codehaus.jackson.JsonFactory; import org.codehaus.jackson.JsonGenerationException; import org.codehaus.jackson.JsonParser; import org.codehaus.jackson.JsonToken; public class JacksonStreamingReadFromFileExample { public static void main(String[] args) { try { JsonFactory jfactory = new JsonFactory(); System.out.println("Reading data from json file"); System.out.println("--------------------------"); JsonParser jParser = jfactory .createJsonParser(new File("//Users//Arpit//countryStreaming.json")); // We need to loop until we reach to the end object. while (jParser.nextToken() != JsonToken.END_OBJECT) { String fieldname = jParser.getCurrentName(); if ("name".equals(fieldname)) { jParser.nextToken(); System.out.println("Name of Country:"+jParser.getText()); } if ("population".equals(fieldname)) { jParser.nextToken(); System.out.println("Population: "+jParser.getText()); } // reading the listOfStates which is an array if ("listOfStates".equals(fieldname)) { // current token is "[" beginning of array. So we wii go to next jParser.nextToken(); System.out.println("List of states:"); // iterate through the array until token equal to "]" while (jParser.nextToken() != JsonToken.END_ARRAY) { System.out.println(jParser.getText()); } } } jParser.close(); } catch (JsonGenerationException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } } |
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Reading data from json file -------------------------- Name of Country:India Population: 10000 List of states: Madhya Pradesh Maharashtra Rajasthan |
click to begin
20KB .zip
6) Project Structure:
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Arpit,
Can we do this without using Maven? if yes, Please provide few tutorials on JSON without Maven build.
You can go to maven central repository – http://search.maven.org/ – and for each of the listed dependencies search for their associated versions. When you find them in the repository there will be a link to allow you to download the jar file manually.
Once you have them downloaded locally you just set your classpath to their location when you run the program or configure your development environment to look at the location when it builds or launches the app.