Spring MVC – Getting Cryptocurrency Details using REST API

Cryptocurrencies are a hot topic throughout the world. Trading with cryptocurrency got both pros and cons. Nowadays REST APIs are very useful to get much information including cryptocurrencies. In this article, we are going to see about one such REST API call to get cryptocurrency detail. We are going to retrieve the information by using Spring MVC. Examples of cryptocurrency:

• Bitcoin (BTC)
• Litecoin (LTC)
• Ethereum (ETH)
• Zcash (ZEC)
• and many more

By using the above URL, let us try to give the cryptocurrency name and check the output

https://api.coincap.io/v2/assets/bitcoin

It produces the JSON output and it is given below

Now for our Spring MVC implementation of retrieving REST API calls, let’s show the below details like

Rank      : 1
Symbol    : BTC
Price(USD): 23016.1293786598184909

Step by Step Implementation

Via a Maven-driven project, implementation is getting done. Let’s start with the project structure

Project Structure:

As it is a maven-driven project, let us go with pom.xml

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.cryptocurrency.cryptocurrency_Rest_API</groupId>
    <artifactId>cryptocurrency_Rest_API</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>CryptoDetails</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>
            <!-- This should be added to overcome Could not initialize class
                  org.apache.maven.plugin.war.util.WebappStructureSerializer -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>3.3.2</version>
            </plugin>
        </plugins>
    </build>
</project>

Invocation file: findCryptoDetails.jsp

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>Cryptocurrency</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;
        }
        .main-form {
            margin: 50px auto 0px;
        }
        .profile-area {
            margin: 10px auto;
        }
        .main-form section, .profile-area section {
            margin-bottom: 15px;
            background: #1BA330;
            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;
            font-family: verdana;
        }
        .hideElement {
            display: none;
        }
    </style>
</head>
<body>
<div class="main-form" id="main-form">
    <section>
        <h5 class="text-center">Enter Cryptocurrency</h5>
        <div class="form-group">
            <input id="cryptocurrency" type="text" class="form-control" placeholder="Enter cryptocurrency here..." required="required">
        </div>
        <div class="form-group">
            <button onclick="loadData()" class="btn btn-primary btn-block">Find Cryptocurrency 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>Rank        : </strong><span id="rank"></span></p>


<p><strong>Symbol     : </strong><span id="symbol"></span></p>


<p><strong>Price(USD): </strong><span id="priceUsd"></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 cryptocurrency = document.getElementById("cryptocurrency").value;

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

This JSP file has to be run on any web server like Tomcat. On execution of the file, we can see the below output.

Output:

We need to give cryptocurrency value here. It can be bitcoin or ethereum etc.,

Let us check for bitcoin

Let us see the important java files that got used for the project

AppConfig.java

Java

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;

@Configuration
@EnableWebMvc
@ComponentScan(basePackages = { "com.cryptocurrency.cryptocurrency_Rest_API" })
public class AppConfig {
    @Bean
    public InternalResourceViewResolver resolver() {
        InternalResourceViewResolver resolver = new InternalResourceViewResolver();
        resolver.setViewClass(JstlView.class);
        resolver.setPrefix("/");
        resolver.setSuffix(".jsp");
        return resolver;
    }
}

SpringMvcDispatcherServletInitializer.java

Java

import org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer;

public class SpringMvcDispatcherServletInitializer
      extends AbstractAnnotationConfigDispatcherServletInitializer {
    @Override
    protected Class<?>[] getRootConfigClasses() {
        return null;
    }
    @Override
    protected Class<?>[] getServletConfigClasses() {
        return new Class[] { AppConfig.class };
    }
    @Override
    protected String[] getServletMappings() {
        return new String[] { "/" };
    }
}

CryptocurrencyController.java

Java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.StringTokenizer;
import org.springframework.stereotype.Controller;
import org.springframework.util.StringUtils;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import com.google.gson.Gson;
import com.google.gson.JsonObject;

@Controller
public class CryptocurrencyController {

    @RequestMapping("/getCryptocurrencyDetailsByName")
    public @ResponseBody
    JsonObject getCryptocurrencyDetails(String  cryptocurrency) throws IOException {

        JsonObject jsonObject = new JsonObject();
        String data = getCryptocurrencyData(cryptocurrency);

        // Once we receive the data we need to parse that
        // and hence these special characters has to be removed
        data = data.replaceAll("^\"|\"$", "");
        StringTokenizer jsonTokenizer = new StringTokenizer(data,",");
        String internalData[];
        String expectedCryptocurrencyOutput = null;

        // After parsing, retrieving Rank, Symbol and priceUsd from it
        while (jsonTokenizer.hasMoreTokens()) {
            expectedCryptocurrencyOutput = jsonTokenizer.nextToken();
            internalData = StringUtils.split(expectedCryptocurrencyOutput,":");
            System.out.println(internalData[0]+internalData[1]);
            if (internalData[0].substring(1,internalData[0].length()-1).equalsIgnoreCase("rank")) {
                jsonObject.addProperty("rank", internalData[1].substring(1,internalData[1].length()-1));

            }
            if (internalData[0].substring(1,internalData[0].length()-1).equalsIgnoreCase("symbol")) {
                jsonObject.addProperty("symbol", internalData[1].substring(1,internalData[1].length()-1));
            }
            if (internalData[0].substring(1,internalData[0].length()-1).equalsIgnoreCase("priceUsd")) {
                jsonObject.addProperty("priceUsd", internalData[1].substring(1,internalData[1].length()-1));
            }
        }

        jsonObject.addProperty("data", data);

        return jsonObject;
    }

    private String getCryptocurrencyData(String cryptocurrency) throws IOException {

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

        // REST API call that got used along with the search string
        url = new URL("https://api.coincap.io/v2/assets/"+cryptocurrency);
        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 (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);
            data = jsonObject.get("data").toString();
        }
        System.out.println(data);
        return data;
    }
}

Conclusion

REST APIs are lightweight, independent, highly scalable, and flexible. Because of these reasons, quite often required data are obtained via REST API. Many are available as open source calls. For a few, we need to get a proper API key (for security reasons) and also there are limitations in using that calls. The one which we covered is totally open-source and hence Spring Framework can easily retrieve the data using a parsing mechanism, the required data is getting displayed on the screen.