RESTful Web Services JSON API Transformer with Java

This post is the continuation of my previous last post, I had explained how to create a basic RESTful web services API using Java, now I want to explain JSON transformer to work with input Get and Post methods parameters. Just added a new class called transformer it converts object data into JSON text output format.

Download War File    Download Project Source

Database
Sample database messages table contains three columns msg_id, message and user_id_fk.

CREATE TABLE  `messages` (
`msg_id` int(11) NOT NULL AUTO_INCREMENT,
`message` TEXT,
`user_id_fk` INT,
PRIMARY KEY (`msg_id`)
);

This tutorial required RESTful service support JAR files jersey-client-1.0.3.jar, jersey-core-1.0.3.jar, jersey-server-1.0.3.jar(Download), jsr311-api-1.0.jar(Download) and asm-3.1.jar(Download). Copy these files into WEB-INF -> lib



Download Project Source link contains all these JARs.

Previous Tutorials: Java MySQL Insert Record using Jquery. and Java MySQL JSON Display Records using Jquery.

Package structure for more details please check my previous java tutorials.


FeedObjects.java
Create a new package called dto (Data Transaction Objects). Created transaction objects title, description and url.

package dto;

public class FeedObjects {

private String msg_id;
private String message;
private String user_id;

//Generate Getters and Setters
}

Explained generating Getters and Setter methods in this following tutorialJava MySQL JSON Display Records using Jquery.

Project.java
Create a dao(Data Access Object) method GetFeeds with Arraylist datatype, using select statement getting results from messageses table where user_id_fk. Binding results into feedData object.

package dao;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;

import dto.FeedObjects;

public class Project
{
public ArrayList<feedobjects> GetFeeds(Connection connection,,String User_ID) throws Exception
{
ArrayList<feedobjects> feedData = new ArrayList<feedobjects>();
try
{
PreparedStatement ps = connection.prepareStatement("SELECT msg_id,message,user_id_fk FROM messages WHERE user_id_fk=? ORDER BY msg_id DESC");
ps.setString(1,User_ID);
ResultSet rs = ps.executeQuery();
while(rs.next())
{
FeedObjects feedObject = new FeedObjects();
feedObject.setTitle(rs.getString("msg_id"));
feedObject.setDescription(rs.getString("message"));
feedObject.setUrl(rs.getString("user_id_fk"));
feedData.add(feedObject);
}
return feedData;
}
catch(Exception e)
{
throw e;
}
}

}

ProjectManager.java
Model class write the business logic and data validation.

package model;

import java.sql.Connection;
import java.util.ArrayList;

import dao.Database;
import dao.Project;
import dto.FeedObjects;

public class ProjectManager {

public ArrayList<feedobjects> GetFeeds(String User_Id)throws Exception {
ArrayList<feedobjects> feeds = null;
try {
Database database= new Database();
Connection connection = database.Get_Connection();
Project project= new Project();
feeds=project.GetFeeds(connection,User_Id);
}
catch (Exception e) {
throw e;
}
return feeds;
}

}

FeedTransformer.java
Transformer class converts Java object result into JSON text format.

package transformer;

import java.util.ArrayList;
import com.google.gson.Gson;

import dto.FeedObjects;

public class FeedTransformer
{
public static String UserFeed(ArrayList<FeedObjects> feedData)
{
String feeds = null;
Gson gson = new Gson();
feeds = gson.toJson(feedData);
return feeds;
}
}

FeedService.java
Web Services class for RESTful API.

package webService;

import java.util.ArrayList;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.QueryParam;

import model.ProjectManager;
import com.google.gson.Gson;
import dto.FeedObjects;

@Path("/WebService")
public class FeedService {

@GET
@Path("/GetFeeds")
@Produces("application/json")
public String messageFeed(@QueryParam("userId") String User_Id)
{
String feeds = null;
try
{

ArrayList<FeedObjects> feedData = null;

ProjectManager projectManager= new ProjectManager();

feedData = projectManager.GetFeeds(User_Id);

feeds=FeedTransformer.UserFeed(feedData);

}
catch (Exception e)
{
System.out.println("Exception Error"); //Console 
}
return feeds;
}

}

If you want to convert GET to POST just do little change.

import javax.ws.rs.GET;
import javax.ws.rs.QueryParam;
to
import javax.ws.rs.POST;
import javax.ws.rs.FormParam;

@GET
@Path("/GetFeeds")
to
@POST
@Path("/GetFeeds")


public String messageFeed(@QueryParam("userId") String User_Id)
to
public String messageFeed(@FormParam("userId") String User_Id)

You can test post method with Mozilla Firefox Add on Poster.

web.xml
The URL configuration file.

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
<display-name>FirstProject</display-name>
<welcome-file-list>

<welcome-file>index.html</welcome-file>

<welcome-file>index.htm</welcome-file>

<welcome-file>index.jsp</welcome-file>

</welcome-file-list>

<servlet>

<servlet-name>ServletAdaptor</servlet-name>

<servlet-class>

com.sun.jersey.server.impl.container.servlet.ServletAdaptor</servlet-class>

<load-on-startup>1</load-on-startup>

</servlet>

<servlet-mapping>

<servlet-name>ServletAdaptor</servlet-name>

<url-pattern>/REST/*</url-pattern>

</servlet-mapping>

</web-app>

Final GET URL
http://localhost:8080/RESTfulProject/REST/WebService/GetFeeds

Here RESTfulProject is the project name, REST is the web.xml servelt mapping name, WebService is REST API path and GetFeeds is the method name.

Note: For checking POST URLs user Poster extension for Chrome and Firefox.

JSON Output

[{
"msg_id":"3",
"message":"Everything is possible. ",
"user_id":"2"
},
{
"msg_id":"1",
"message":"Make People fall in love with Your Ideas",
"user_id":"2"
}]

Next post I will explain friendly RESTful web services with path inputs parameters.