OpenSource REST API URL and Retrieving Data From it By Using Spring MVC

In this internet era, a lot of helper services are available in the form of REST API and mostly REST API provides us the details in the form of JSON/XML. We can use them in our applications and render the data as we like. Here is the list of a few opensource REST API URLs:

API Name	Description	URL
CoinGecko	Exchange rates	https://api.coingecko.com/api/v3/exchange_rates
ExchangeRate-API	Exchange rates	https://open.er-api.com/v6/latest/INR
Genderize.io	Prediction of gender based on name	https://api.genderize.io?name=rachel
WeatherDB	To know about the weather	https://weatherdbi.herokuapp.com/data/weather/london
Zippopotamus	Zipcode information	https://api.zippopotam.us/IN/600028

There are still more open-source APIs available. Here we will be learning how to extract the zip code details using Spring MVC:

REST API: http://api.zippopotam.us/IN/<Required Pincode>

Example:

http://api.zippopotam.us/IN/600028

Output: JSON

{
  "post code": "600028",
  "country": "India",
  "country abbreviation": "IN",
  "places": [
    {
      "place name": "Fore Shore Estate",
      "longitude": "80.2417",
      "state": "Tamil Nadu",
      "state abbreviation": "TN",
      "latitude": "13.0206"
    },
    {
      "place name": "Ramakrishnanagar",
      "longitude": "80.2417",
      "state": "Tamil Nadu",
      "state abbreviation": "TN",
      "latitude": "13.0206"
    },
    {
      "place name": "R A Puram Colony",
      "longitude": "80.2417",
      "state": "Tamil Nadu",
      "state abbreviation": "TN",
      "latitude": "13.0206"
    }
  ]
}

Now using Spring MVC Framework, let us try to render the REST API details on the screen

Implementation:

It is as depicted Step by Step below where initially let us do see the project structure which is as follows:

A. File: pom.xml

XML

<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/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.zipCode.zipCode_RestAPI</groupId>
    <artifactId>zipCode_RestAPI</artifactId>
    <packaging>war</packaging>
    <version>0.0.1-SNAPSHOT</version>
    <name>profileGenerator</name>
    <url>http://maven.apache.org</url>
    <properties>
        <failOnMissingWebXml>false</failOnMissingWebXml>
        <spring-version>5.1.0.RELEASE</spring-version>
    </properties>
    <dependencies>
        <!-- https://mvnrepository.com/artifact/org.springframework/spring-webmvc -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>${spring-version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-test</artifactId>
            <version>${spring-version}</version>
        </dependency>

        <!-- JSTL Dependency -->
        <dependency>
            <groupId>javax.servlet.jsp.jstl</groupId>
            <artifactId>javax.servlet.jsp.jstl-api</artifactId>
            <version>1.2.1</version>
        </dependency>
        <dependency>
            <groupId>taglibs</groupId>
            <artifactId>standard</artifactId>
            <version>1.1.2</version>
        </dependency>

        <!-- Servlet Dependency -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
            <scope>provided</scope>
        </dependency>

        <!-- JSP Dependency -->
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>javax.servlet.jsp-api</artifactId>
            <version>2.3.1</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>com.google.code.gson</groupId>
            <artifactId>gson</artifactId>
            <version>2.8.6</version>
        </dependency>
        <dependency>
            <groupId>commons-io</groupId>
            <artifactId>commons-io</artifactId>
            <version>2.5</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <build>
        <finalName>Zipcode</finalName>
        <sourceDirectory>src/main/java</sourceDirectory>
        <plugins>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.5.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
            <plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-war-plugin</artifactId>
  <version>3.3.2</version>
</plugin>

      <plugin>
        <groupId>org.codehaus.mojo</groupId>
        <artifactId>tomcat-maven-plugin</artifactId>
        <version>1.0-beta-1</version>
      </plugin>
        </plugins>
    </build>
</project>

B. File: index.jsp

This is the page that gets rendered when the project is deployed in tomcat

HTML

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>ZipCode</title>
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.5.0/css/bootstrap.min.css">
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.5.0/js/bootstrap.min.js"></script>
    <style type="text/css">
        .main-form, .profile-area {
            width: 500px;
            background: #FF5733;

        }
        .main-form {
            margin: 50px auto 0px;
        }
        .profile-area {
            margin: 10px auto;
        }
        .main-form section, .profile-area section {
            margin-bottom: 15px;
            background: #f7f7f7;
            box-shadow: 0px 2px 2px rgba(0, 0, 0, 0.3);
        }
        .main-form section {
            padding: 30px;
        }
        .profile-area section {
            padding: 30px 30px 30px;
        }
        .profile-area section > div {
            text-align: center;
        }
        .main-form h3 {
            margin: 0 0 15px;
        }
        .form-control, .btn {
            min-height: 38px;
            border-radius: 2px;
        }
        .btn {
            font-size: 15px;
            font-weight: bold;
        }
        .hideElement {
            display: none;
        }
    </style>
</head>
<body>
<div class="main-form" id="main-form">
    <section>
        <h5 class="text-center">Enter your zipcode</h5>
        <div class="form-group">
            <input id="zipcode" type="text" class="form-control" placeholder="Enter zipcode here..." required="required">
        </div>
        <div class="form-group">
            <button onclick="loadData()" class="btn btn-primary btn-block">Find Area Details</button>
        </div>
    </section>
</div>
<div class="profile-area hideElement" id="profile-area">
    <section>
        <div id="loader" class="hideElement">
            <div class="spinner-border" role="status">
                <span class="sr-only">Loading...</span>
            </div>
        </div>
        <div id="profile" class="hideElement">
            <br><br>


<p><strong>Country : </strong><span id="country"></span></p>




<p><strong>State    : </strong><span id="statename"></span></p>




<p><strong>Localities : </strong><span id="associatedplaces"></span></p>




<p><strong>Latitude    : </strong><span id="associatedlatitude"></span></p>




<p><strong>Longitude : </strong><span id="associatedlongitude"></span></p>


        </div>
    </section>
</div>
</body>
<script>
    function loadData() {
        document.getElementById("profile-area").classList.remove("hideElement");
        document.getElementById("loader").classList.remove("hideElement");
        document.getElementById("profile").classList.add("hideElement");

        var zipCode = document.getElementById("zipcode").value;

        if(zipCode != "" && zipCode != null) {
            var xhttp = new XMLHttpRequest();
            xhttp.onreadystatechange = function() {
                if (this.readyState == 4 && this.status == 200) {
                    var jsonResponse = JSON.parse(this.responseText);
                    document.getElementById("country").innerHTML = jsonResponse.country;
                    document.getElementById("statename").innerHTML = jsonResponse.statename;
                    document.getElementById("associatedplaces").innerHTML = jsonResponse.associatedplaces;
                    document.getElementById("associatedlatitude").innerHTML = jsonResponse.associatedlatitude;
                    document.getElementById("associatedlongitude").innerHTML = jsonResponse.associatedlongitude;
                    document.getElementById("loader").classList.add("hideElement");
                    document.getElementById("profile").classList.remove("hideElement");
                }
            };
            xhttp.open("GET", "getLocalityDetailsByZipCode?zipCode=" + zipCode, true);
            xhttp.send();
            console.log("done");
        } else {
            console.log("Enter zipcode...")
        }
    }
</script>
</html>

Output:

On entering any valid zip code. For example 600028, name in the input box, we will get the below details.

Execution Process: From the JSP page, a “GET” method is invoked with the search string and it is redirected to the Spring Controller class, where the REST API URL, <a target="_blank" rel="noopener noreferrer nofollow" href="http://api.zippopotam.us/IN/http://api.zippopotam.us/IN/<valid zipcode> is invoked and it will create the JSON object as given above, From that, we are taking “country”, “state”,”latitude”,”longitude” and “localities” values. 

Country : India

State : Tamil Nadu

Localities : [Fore Shore Estate, Ramakrishnanagar, R A Puram Colony]

Latitude : [13.0206, 13.0206, 13.0206]

Longitude : [80.2417, 80.2417, 80.2417]

Output: Screen

Required code for retrieving the data and parsing the JSON output is as follows. Important necessary files to achieve the flow

File: AppConfig.java

Java

// Java Program to Illustrate Application
// configuration Class

// Importing required classes
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;
import org.springframework.web.servlet.view.InternalResourceViewResolver;
import org.springframework.web.servlet.view.JstlView;

// Annotations
@Configuration
@EnableWebMvc
@ComponentScan(basePackages
               = { "com.zipCode.zipCode_RestAPI" })

// Class
public class AppConfig {

    @Bean public InternalResourceViewResolver resolver()
    {

        InternalResourceViewResolver resolver
            = new InternalResourceViewResolver();
        resolver.setViewClass(JstlView.class);
        resolver.setPrefix("/");
        resolver.setSuffix(".jsp");

        return resolver;
    }
}

File: SpringMvcDispatcherServletInitializer.java

Java

// Java Program to Illustrate
// SpringMvcDispatcherServletInitializer Class

// Importing required classes
import org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer;

// Class
public class SpringMvcDispatcherServletInitializer
    extends AbstractAnnotationConfigDispatcherServletInitializer {

    // Method 1
    @Override protected Class<?>[] getRootConfigClasses()
    {
        return null;
    }

    // Method 2
    @Override protected Class<?>[] getServletConfigClasses()
    {
        return new Class[] { AppConfig.class };
    }

    // Method 3
    @Override protected String[] getServletMappings()
    {
        return new String[] { "/" };
    }
}

File: ZipCodeController.java

Java

// Java Program to Illustrate ZipCodeController Class

// Importing required classes
import com.google.gson.Gson;
import com.google.gson.JsonArray;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.Iterator;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

// Annotation
@Controller
// Class
public class ZipCodeController {

    // Method 1
    @RequestMapping("/getLocalityDetailsByZipCode")
    public @ResponseBody
    JsonObject getLocalityDetailsByZipCode(String zipCode)
        throws IOException
    {

        JsonObject jsonObject = new JsonObject();
        jsonObject = getLocalityDetailsByZip(zipCode);

        // Parsing the JSONObject
        JsonObject finalJsonObject = new JsonObject();

        String country
            = jsonObject.get("country").toString();
        country = country.replaceAll("^\"|\"$", "");
        JsonArray jsonPlacesArray = null;

        ArrayList placesList = new ArrayList();
        ArrayList stateList = new ArrayList();
        ArrayList latitudeList = new ArrayList();
        ArrayList longitudeList = new ArrayList();

        // Places data is available as JSONArray
        jsonPlacesArray
            = jsonObject.get("places").getAsJsonArray();
        // It is iterated
        Iterator<JsonElement> objectIterator
            = jsonPlacesArray.iterator();

        while (objectIterator.hasNext()) {
            JsonElement object = objectIterator.next();
            JsonObject jObj = object.getAsJsonObject();
            System.out.println(
                jObj.get("place name").toString()
                + jObj.get("state").toString());
            placesList.add(jObj.get("place name")
                               .toString()
                               .replaceAll("^\"|\"$", ""));
            stateList.add(
                jObj.get("state").toString().replaceAll(
                    "^\"|\"$", ""));
            latitudeList.add(
                jObj.get("latitude")
                    .toString()
                    .replaceAll("^\"|\"$", ""));
            longitudeList.add(
                jObj.get("longitude")
                    .toString()
                    .replaceAll("^\"|\"$", ""));
        }

        finalJsonObject.addProperty("country", country);
        finalJsonObject.addProperty("associatedplaces",
                                    placesList.toString());
        finalJsonObject.addProperty("associatedplacessize",
                                    placesList.size());
        finalJsonObject.addProperty("state",
                                    stateList.toString());
        finalJsonObject.addProperty(
            "statename", stateList.get(0).toString());
        finalJsonObject.addProperty(
            "associatedlatitude", latitudeList.toString());
        finalJsonObject.addProperty(
            "associatedlatitudesize", latitudeList.size());
        finalJsonObject.addProperty(
            "associatedlongitude",
            longitudeList.toString());
        finalJsonObject.addProperty(
            "associatedlongitudesize",
            longitudeList.size());

        return finalJsonObject;
    }

    // Method 2
    private JsonObject
    getLocalityDetailsByZip(String zipCode)
        throws IOException
    {

        String data = null;
        StringBuilder responseData = new StringBuilder();
        JsonObject jsonObject = null;

        URL url = null;
        url = new URL("http://api.zippopotam.us/IN/"
                      + zipCode);

        HttpURLConnection con
            = (HttpURLConnection)url.openConnection();
        con.setRequestMethod("GET");
        con.setRequestProperty("User-Agent", "Mozilla/5.0");
        int responseCode = con.getResponseCode();

        System.out.println(
            "\nSending 'GET' request to URL : " + url);
        //        System.out.println("Response Code : " +
        //        responseCode);

        // Try block to check for exceptions
        try (BufferedReader in
             = new BufferedReader(new InputStreamReader(
                 con.getInputStream()))) {

            String line;

            while ((line = in.readLine()) != null) {
                responseData.append(line);
            }

            jsonObject = new Gson().fromJson(
                responseData.toString(), JsonObject.class);
        }

        // System.out.println(data);
        return jsonObject;
    }
}

Conclusion: This process of code is required for retrieving any REST API call. We need to know whether REST API provides either JSONObject/JSONArray and accordingly we have to parse the data.