Jackson project has implemented a very useful Streaming API which is also called incremental mode. This is the most efficient way to process JSON content. It has the lowest memory and processing overhead, and can often match performance of many binary data formats available on Java platform. It’s a bit tricky to use though because you have to handle JSON data in all it’s details.
In this example we are going to use JsonGenerator to write a JSON representation to a file and JsonParser to parse a file ton JSON representation.
1. Create a JSON representation and write it to a File
JacksonStreamAPIExample.java:
package com.javacodegeeks.java.core;
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.map.JsonMappingException;
public class JacksonStreamAPIExample {
private static final String jsonFilePath = "C:\\Users\\nikos7\\Desktop\\filesForExamples\\jsonFile.json";
public static void main(String[] args) {
try {
JsonFactory jsonfactory = new JsonFactory();
File jsonFile = new File(jsonFilePath);
JsonGenerator jsonGenerator = jsonfactory.createJsonGenerator(jsonFile, JsonEncoding.UTF8);
jsonGenerator.writeStartObject();
jsonGenerator.writeStringField("domain", "javacodegeeks.com");
jsonGenerator.writeNumberField("members", 200);
jsonGenerator.writeFieldName("names");
jsonGenerator.writeStartArray();
jsonGenerator.writeString("John");
jsonGenerator.writeString("Jack");
jsonGenerator.writeString("James");
jsonGenerator.writeEndArray();
jsonGenerator.writeEndObject();
jsonGenerator.close();
System.out.println("The file was created successfully");
} catch (JsonGenerationException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}jsonFile.json:
{"domain":"javacodegeeks.com","members":200,"names":["John","Jack","James"]}2. Parse a JSON file
This is the tricky part in the Streaming API. In this, every single string is considered a token. It’s a classic parsing procedure.
We are going to use jsonFile.json as an input file for the demp.
Let’s see the code:
JacksonStreamAPIExample.java:
package com.javacodegeeks.java.core;
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;
import org.codehaus.jackson.map.JsonMappingException;
public class JacksonStreamAPIExample {
private static final String jsonFilePath = "C:\\Users\\nikos7\\Desktop\\filesForExamples\\jsonFile.json";
public static void main(String[] args) {
try {
JsonFactory jsonfactory = new JsonFactory();
//input file
File jsonFile = new File(jsonFilePath);
JsonParser jsonParser = jsonfactory.createJsonParser(jsonFile);
// Begin the parsing procedure
while (jsonParser.nextToken() != JsonToken.END_OBJECT) {
String token = jsonParser.getCurrentName();
if ("domain".equals(token)) {
// get the next token which will be the value...
jsonParser.nextToken();
System.out.println("domain : "+jsonParser.getText());
}
if ("members".equals(token)) {
jsonParser.nextToken();
System.out.println("members : " + jsonParser.getIntValue());
}
if ("names".equals(token)) {
System.out.println("names :");
//the next token will be '[' that means that we have an array
jsonParser.nextToken();
// parse tokens until you find ']'
while (jsonParser.nextToken() != JsonToken.END_ARRAY) {
System.out.println(jsonParser.getText());
}
}
}
jsonParser.close();
} catch (JsonGenerationException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}output:
domain : javacodegeeks.com
members : 200
names :
John
Jack
James
This was an example on how to use Jackson Streaming API to read and write JSON.
current examples doesn’t work in l.8 java