- REST calls can be made over HTTP.
- REST is language independent, so the client and server application can use any programming language.
- REST application can use any data format, but commonly use XML and JSON.
- XML (Extensible Markup Language)
- JSON (JavaScript Object Notation)
- We can find REST APIs on ProgrammableWeb
JSON (JavaScript Object Notation) is a lightweight data format for storing and exchanging data in plain text. It's language independent and not just for JavaScript. Let's see an example:
{
"id": 14,
"firstName": "Mario",
"lastName": "Rossi",
"active": true,
"languages": ["Java", "C#", "Python", "JavaScript"],
"address": {
"street": "100 Main St",
"city": "Philadelphia",
"state": "Pennsylvania",
"zip": "19103",
"country": "USA"
},
"courses": null
}- Use curley braces define objects in JSON.
- Object members are name/value pairs delimited by colons.
- Name should always in double-quotes.
- Arrays member use square brackets.
Data binding is the process of converting JSON data to a Java POJO. Spring uses the Jackson Project behind the JSON behind the scenes. The Jackson data binding API located with package com.fasterxml.jackson.databind and can be added with Maven Dependency:
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.12.4</version>
</dependency>By default, Jackson will call appropriate getter/setter method for data binding instead of accessing internal private fields directly:
// create object mapper
ObjectMapper mapper = new ObjectMapper();
// read JSON from file and map/convert to Java POJO
Student myStudent = mapper.readValue(new File("data/sample.json"), Student.class);
...
// write JSON to output file
mapper.enable(SerializationFeature.INDENT_OUTPUT);
mapper.writeValue(new File("data/output.json"), myStudent);- Spring will automatically handle Jackson Integration when building Spring REST applications.
- JSON data being passed to REST controller is converted to Java POJO.
- Java object being returned from REST controller is converted to JSON.