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14. [TD]: Web exposure of the [metier] layer

Keywords: multi-tier architecture, Spring, dependency injection, web service / jSON, client / server.

Let’s return to the current architecture of the TD application:

We will evolve this architecture into the following:

in order to expose the [IMetier] interface of the business layer on the web. To do this, we will follow the methodology described in section 13.5.

14.1. Support

  

The projects in this chapter can be found in the [support / chap-14] folder.

14.2. The Eclipse project for the [métier] layer

  

14.2.1. Maven Configuration

The [métier] layer project is a Maven project configured by the following [pom.xml] file:


<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <modelVersion>4.0.0</modelVersion>
    <groupId>istia.st.elections</groupId>
    <artifactId>elections-metier-dao-spring-data</artifactId>
    <version>0.1.0</version>
 
    <!-- dependencies -->
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.2.7.RELEASE</version>
    </parent>
    <dependencies>
        <!-- layer [DAO] -->
        <dependency>
            <groupId>istia.st.elections</groupId>
            <artifactId>elections-dao-spring-data-01</artifactId>
            <version>0.0.1-SNAPSHOT</version>
        </dependency>
        <!-- Spring Boot -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot</artifactId>
            <scope>test</scope>
        </dependency>
        <!-- Spring Boot Test -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>
 
    <properties>
        <!-- use UTF-8 for everything -->
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
    </properties>
 
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>2.18.1</version>
            </plugin>
        </plugins>
    </build>
</project>
  • lines 18–22: the dependency on the [DAO] layer built in paragraph 12;
  • lines 23–34: the dependencies required for testing;

14.2.2. Spring Configuration

  

The [métier] layer project is a Spring project configured by the following [MetierConfig] file:


package elections.metier.config;
 
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Import;
 
import elections.dao.config.DaoConfig;
 
@Import({ DaoConfig.class })
@ComponentScan({ "elections.metier.service" })
public class MetierConfig {
}
  • We do not use the [@Configuration] annotation here, which would make the class a Spring configuration class. The presence of the [@Import, @ComponentScan] annotations automatically makes it a configuration class;
  • line 8: we import the configuration file from the [DAO] layer. We then have access to all the beans defined by this file;
  • line 9: other Spring beans are to be found in the [elections.metier.service] folder;

14.2.3. Implementation of the [métier] layer

  

The implementation of the [métier] layer is the one defined in Section 8.5.

14.2.4. Testing the [métier] layer

  

The test class is the one described in Section 8.6.

Task: Implement the [métier] layer project and pass its unit test. Generate the layer archive in the local Maven repository (run as/Maven/install).

14.3. The Eclipse project for the [web] layer

The web layer is a Spring layer MVC:

The Eclipse project has the following structure:

  • [Boot.java] is the class that launches the web service;
  • [WebConfig.java] is the web service configuration class;
  • [Response.java] is the response generated by the various URL components of the web service;
  • [ElectionsController] is the web service implementation class;

14.4. Maven Configuration

The project is a Maven project configured by the following [pom.xml] file:


<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/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>istia.st.elections</groupId>
    <artifactId>elections-webjson-metier-dao-spring-data</artifactId>
    <version>0.0.1-SNAPSHOT</version>
 
    <name>elections-webjson-metier-dao-spring-data</name>
    <description>couche métier exposée comme un service web / jSON</description>
 
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.2.7.RELEASE</version>
    </parent>
 
    <dependencies>
        <!-- business layer -->
        <dependency>
            <groupId>istia.st.elections</groupId>
            <artifactId>elections-metier-dao-spring-data</artifactId>
            <version>0.1.0</version>
        </dependency>
        <!-- layer MVC -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>
 
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
    </properties>
 
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>2.18.1</version>
            </plugin>
        </plugins>
    </build>
 
</project>
  • lines 19–23: the dependency on the [métier] layer archive. This is the one we created in paragraph 14;
  • lines 25–28: the dependency for the Spring application MVC;

14.5. Spring Configuration

 

The [WebConfig] class configures the web service:


package elections.webjson.config;
 
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.boot.context.embedded.EmbeddedServletContainerFactory;
import org.springframework.boot.context.embedded.ServletRegistrationBean;
import org.springframework.boot.context.embedded.tomcat.TomcatEmbeddedServletContainerFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Import;
import org.springframework.context.annotation.Scope;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.servlet.DispatcherServlet;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;

import com.fasterxml.jackson.databind.ObjectMapper;
 
import elections.metier.config.MetierConfig;
 
@EnableWebMvc
@Import({ MetierConfig.class })
@ComponentScan({ "elections.webjson.service" })
public class WebConfig {
    // -------------------------------- layer configuration [web]
    @Autowired
    private ApplicationContext context;
 
    @Bean
    public DispatcherServlet dispatcherServlet() {
        DispatcherServlet servlet = new DispatcherServlet((WebApplicationContext) context);
        return servlet;
    }
 
    @Bean
    public ServletRegistrationBean servletRegistrationBean(DispatcherServlet dispatcherServlet) {
        return new ServletRegistrationBean(dispatcherServlet, "/*");
    }
 
    @Bean
    public EmbeddedServletContainerFactory embeddedServletContainerFactory() {
        return new TomcatEmbeddedServletContainerFactory("", 8080);
    }
    // mapper jSON
    @Bean
    @Scope(value = ConfigurableBeanFactory.SCOPE_PROTOTYPE)
    public ObjectMapper jsonMapper() {
        return new ObjectMapper();
    }
 
}
  1. The meaning of this configuration was explained in section 13.5.3.1. We will only explain the new features:
  2. line 22: we import the configuration file for the [métier] layer to make use of all its beans;
  3. line 23: we specify that other beans will be found in the [elections.webjson.server.service] folder;

14.6. The web service launch class

 

The [Boot] class launches the web service as follows:


package elections.webjson.boot;
 
import org.springframework.boot.SpringApplication;
 
import elections.webjson.config.WebConfig;
 
public class Boot {
 
    public static void main(String[] args) {
        SpringApplication.run(WebConfig.class, args);
    }
}
  1. Line 10: The static method [SpringApplication.run] will use the configuration file [WebConfig]. Because of the annotation [@EnableAutoConfiguration], Spring Boot will start the Tomcat server and deploy the web service on it;

14.7. The response from the URL of the web service

 

All URL requests from the web service / jSON send the same type of response:


package elections.webjson.service;
 
import java.util.List;
 
public class Response<T> {
 
    // ----------------- properties
    // operation status
    private int status;
    // any error messages
    private List<String> messages;
    // the body of the reply
    private T body;
 
    // manufacturers
    public Response() {
 
    }
 
    public Response(int status, List<String> messages, T body) {
        this.status = status;
        this.messages = messages;
        this.body = body;
    }
 
    // getters and setters
...
}

This class was introduced and discussed in Section 13.5.5.3.

14.8. Implementation of the web service / jSON

 

The web service / jSON is implemented by the following class [ElectionsController]:


package elections.webjson.service;
 
import java.util.ArrayList;
import java.util.List;
 
import javax.servlet.http.HttpServletRequest;
 
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;
 
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
 
import elections.dao.entities.ElectionsConfig;
import elections.dao.entities.ElectionsException;
import elections.metier.service.IElectionsMetier;
 
@Controller
public class ElectionsController {
 
    // spring dependencies
    @Autowired
    private ObjectMapper jsonMapper;
 
    @Autowired
    private IElectionsMetier metier;
 
    @RequestMapping(value = "/getElectionsConfig", method = RequestMethod.GET, produces = "application/json; charset=UTF-8")
    @ResponseBody
    public String getElectionsConfig() throws JsonProcessingException {
        // answer
        Response<ElectionsConfig> response;
        try {
            response = new Response<>(0, null,
                    new ElectionsConfig(metier.getNbSiegesAPourvoir(), metier.getSeuilElectoral()));
        } catch (ElectionsException e1) {
            response = new Response<>(e1.getCode(), e1.getErreurs(), null);
        } catch (RuntimeException e2) {
            response = new Response<>(1000, getErreursForException(e2), null);
        }
        // answer
        return jsonMapper.writeValueAsString(response);
    }
 
    @RequestMapping(value = "/getListesElectorales", method = RequestMethod.GET, produces = "application/json; charset=UTF-8")
    @ResponseBody
    public String getListesElectorales() throws JsonProcessingException {
        throw new UnsupportedOperationException("Not supported yet");
    }
 
    @RequestMapping(value = "/setListesElectorales", method = RequestMethod.POST, consumes = "application/json; charset=UTF-8", produces = "application/json; charset=UTF-8")
    @ResponseBody
    public String setListesElectorales(HttpServletRequest request) throws JsonProcessingException {
        throw new UnsupportedOperationException("Not supported yet");
    }
 
    @RequestMapping(value = "/calculerSieges", method = RequestMethod.POST, consumes = "application/json; charset=UTF-8", produces = "application/json; charset=UTF-8")
    @ResponseBody
    public String calculerSieges(HttpServletRequest request) throws JsonProcessingException {
        throw new UnsupportedOperationException("Not supported yet");
    }
 
    // private methods -----------------------------
    // list of RuntimeException error messages
    private List<String> getErreursForException(Exception e) {
        // retrieve the list of exception error messages
        Throwable cause = e;
        List<String> erreurs = new ArrayList<>();
        while (cause != null) {
            // the message is retrieved only if it is !=null and not blank
            String message = cause.getMessage();
            if (message != null) {
                message = message.trim();
                if (message.length() != 0) {
                    erreurs.add(message);
                }
            }
            // next cause
            cause = cause.getCause();
        }
        return erreurs;
    }
 
}

Task: Following the steps in Section 13.5.5, complete the code for the [ElectionsController] class.

Notes:

  1. There are no jSON filters here because the tables [CONF] and [LISTES] are not linked by a foreign key relationship, which significantly simplifies the web service code;
  2. Do not forget the various necessary Spring annotations;
  3. We will name the URL methods after their associated methods;
  4. The [setListeElectorales] method is called with a [POST] operation. The posted value is the array of competing lists (of type ListeElectorale[]) with their [sieges, voix, elimine] attributes, which must be saved to the database. This method returns a type [Response<Void>] with a field [status=0] if there were no errors, otherwise something else;
  5. The [calculerSieges] method is called with a [POST] operation. The posted value is the array of competing lists (of type ListeElectorale[]) with their [nom, voix] attributes. This method returns a [Response<ListeElectorale[]>] type with, as its body, the electoral lists with their [sieges, elimine] fields initialized;

14.9. Tests

After launching the web service, perform the following tests to ensure the web service is functioning properly using the [Advanced Rest Client] utility:

 

The response jSON to the previous request is as follows [1]:

1
2

In [2], copy the response to the clipboard, then paste it into any text editor [3]:

Isolate the value of the [body] field and change, for example, the votes for the lists. Below [4], we set the votes for all lists to 100:

Verify that your string jSON begins with [ et se termine par ]. These characters are used to delimit an array jSON. In [5], paste the string jSON above. This will be the value posted for the next URL. To do this, select the method HTTP [POST] [7].

  • In [6], request URL [setListesElectorales]. This URL is requested with a POST. The posted value is the jSON table of competing lists whose results must be recorded in the database;

The following result is obtained:

 

The [status=0] field indicates that there were no errors. To verify this, request the competing lists again and check that the changes you made to the lists have been applied:

We run [POST] again to calculate the seats won by the lists:

  1. in [1]: the URL from the seat calculation;
  2. in [2]: run a [POST];
  3. in [3]: the competing lists. We assign the values from TD to the [voix] field, all [sieges] fields are set to 0, and all [elimine] fields are set to false;

The result is as follows:

 
https://stahe.github.io
This tutorial written by Serge Tahé is made available to the public under the terms of the Creative Commons Attribution – Non-Commercial – ShareAlike 3.0 Unported.