Simple CRUD example with Java RESTful Web Service

The objective of the example
Create Maven Project
Declare Maven & web.xml
Web service classes
Configure to run applications
Test application

1. The objective of the example

In the post, I give you a simple example of RESTful Web Service with the functions as Create + Read + Update + Delete (CRUD).

The techniques used:

Jersey RESTful API
JAXB

JAXB (Java Architecture for XML Binding) is open source Java API , it was officially incorporated into the Java Standard edition (JSE) from version 1.6.

JAXB that transforms Java objects into XML and vice versa. You can see the instructions about JAXB here:
Java JAXB

In RESTful web service with Jersey, JAXB is the default XML-Binding used to convert a Java object into XML and vice versa.

Convert List to XML

In RESTful web service with Jersey, MOXy is the default JSON-Binding used to convert a Java object into JSON and vice versa.

REST services will convert Java Objects into JSON and vice versa automatically. You do not have to attach any Annotation to "model" classes.

2. Create Maven Project

In Eclipse select:

File/New/Other..

Make sure that your Project uses Java >= 1.6 because the JAXB libary has been already integrated into Java since version 1.6.
Project Properties/Project Facet:

3. Declare Maven & web.xml

Declare JERSEY servlet in web.xml:

web.xml

<?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_3_0.xsd"
    version="3.0">

    <display-name>RESTful CRUD Example</display-name>

    <servlet>
        <servlet-name>jerseyServlet</servlet-name>
        <servlet-class>com.sun.jersey.spi.container.servlet.ServletContainer</servlet-class>
        <init-param>
            <param-name>com.sun.jersey.config.property.packages</param-name>
            <param-value>org.o7planning.restfulcrud</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup> 
    </servlet>
    <servlet-mapping>
        <servlet-name>jerseyServlet</servlet-name>
        <url-pattern>/rest/*</url-pattern>
    </servlet-mapping>


</web-app>

pom.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>org.o7planning</groupId>
  <artifactId>RESTfulCRUD</artifactId>
  <packaging>war</packaging>
  <version>0.0.1-SNAPSHOT</version>
  <name>RESTfulCRUD Maven Webapp</name>
  <url>http://maven.apache.org</url>

    <dependencies>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>



        <!-- https://mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
            <scope>provided</scope>
        </dependency>

        <!-- https://mvnrepository.com/artifact/asm/asm -->
        <dependency>
            <groupId>asm</groupId>
            <artifactId>asm</artifactId>
            <version>3.3.1</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/com.sun.jersey/jersey-bundle -->
        <dependency>
            <groupId>com.sun.jersey</groupId>
            <artifactId>jersey-bundle</artifactId>
            <version>1.19.2</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.json/json -->
        <dependency>
            <groupId>org.json</groupId>
            <artifactId>json</artifactId>
            <version>20160810</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/com.sun.jersey/jersey-server -->
        <dependency>
            <groupId>com.sun.jersey</groupId>
            <artifactId>jersey-server</artifactId>
            <version>1.19.2</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/com.sun.jersey/jersey-core -->
        <dependency>
            <groupId>com.sun.jersey</groupId>
            <artifactId>jersey-core</artifactId>
            <version>1.19.2</version>
        </dependency>


        <!-- https://mvnrepository.com/artifact/org.codehaus.jackson/jackson-mapper-asl -->
        <dependency>
            <groupId>org.codehaus.jackson</groupId>
            <artifactId>jackson-mapper-asl</artifactId>
            <version>1.9.13</version>
        </dependency>


    </dependencies>

    <build>
        <finalName>RESTfulCRUD</finalName>
        <plugins>
            <plugin>
                <groupId>org.apache.tomcat.maven</groupId>
                <artifactId>tomcat7-maven-plugin</artifactId>
                <version>2.2</version>
                <configuration>
                    <path>/RESTfulCRUD</path>
                    <port>8080</port>
                </configuration>
            </plugin>

        </plugins>
    </build>


</project>

4. Web service classes

EmployeeDAO.java

package org.o7planning.restfulcrud.dao;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.o7planning.restfulcrud.model.Employee;

public class EmployeeDAO {

    private static final Map<String, Employee> empMap = new HashMap<String, Employee>();

    static {
        initEmps();
    }

    private static void initEmps() {
        Employee emp1 = new Employee("E01", "Smith", "Clerk");
        Employee emp2 = new Employee("E02", "Allen", "Salesman");
        Employee emp3 = new Employee("E03", "Jones", "Manager");

        empMap.put(emp1.getEmpNo(), emp1);
        empMap.put(emp2.getEmpNo(), emp2);
        empMap.put(emp3.getEmpNo(), emp3);
    }

    public static Employee getEmployee(String empNo) {
        return empMap.get(empNo);
    }

    public static Employee addEmployee(Employee emp) {
        empMap.put(emp.getEmpNo(), emp);
        return emp;
    }

    public static Employee updateEmployee(Employee emp) {
        empMap.put(emp.getEmpNo(), emp);
        return emp;
    }

    public static void deleteEmployee(String empNo) {
        empMap.remove(empNo);
    }

    public static List<Employee> getAllEmployees() {
        Collection<Employee> c = empMap.values();
        List<Employee> list = new ArrayList<Employee>();
        list.addAll(c);
        return list;
    }
    
    List<Employee> list;

}

Employee.java

package org.o7planning.restfulcrud.model;

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement(name = "employee")
@XmlAccessorType(XmlAccessType.FIELD)
public class Employee {

    private String empNo;
    private String empName;
    private String position;

    // This default constructor is required if there are other constructors.
    public Employee() {

    }

    public Employee(String empNo, String empName, String position) {
        this.empNo = empNo;
        this.empName = empName;
        this.position = position;
    }

    public String getEmpNo() {
        return empNo;
    }

    public void setEmpNo(String empNo) {
        this.empNo = empNo;
    }

    public String getEmpName() {
        return empName;
    }

    public void setEmpName(String empName) {
        this.empName = empName;
    }

    public String getPosition() {
        return position;
    }

    public void setPosition(String position) {
        this.position = position;
    }

}

Employee Service is a RESTful web service, which supports both XML and JSON formats.

EmployeeService.java

package org.o7planning.restfulcrud.service;

import java.util.List;

import javax.ws.rs.DELETE;
import javax.ws.rs.GET;
import javax.ws.rs.POST;
import javax.ws.rs.PUT;
import javax.ws.rs.Path;
import javax.ws.rs.PathParam;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;

import org.o7planning.restfulcrud.dao.EmployeeDAO;
import org.o7planning.restfulcrud.model.Employee;

@Path("/employees")
public class EmployeeService {

    // URI:
    // /contextPath/servletPath/employees
    @GET
    @Produces({ MediaType.APPLICATION_JSON, MediaType.APPLICATION_XML })
    public List<Employee> getEmployees_JSON() {
        List<Employee> listOfCountries = EmployeeDAO.getAllEmployees();
        return listOfCountries;
    }

    // URI:
    // /contextPath/servletPath/employees/{empNo}
    @GET
    @Path("/{empNo}")
    @Produces({ MediaType.APPLICATION_JSON, MediaType.APPLICATION_XML })
    public Employee getEmployee(@PathParam("empNo") String empNo) {
        return EmployeeDAO.getEmployee(empNo);
    }

    // URI:
    // /contextPath/servletPath/employees
    @POST
    @Produces({ MediaType.APPLICATION_JSON, MediaType.APPLICATION_XML })
    public Employee addEmployee(Employee emp) {
        return EmployeeDAO.addEmployee(emp);
    }

    // URI:
    // /contextPath/servletPath/employees
    @PUT
    @Produces({ MediaType.APPLICATION_JSON, MediaType.APPLICATION_XML })
    public Employee updateEmployee(Employee emp) {
        return EmployeeDAO.updateEmployee(emp);
    }

    @DELETE
    @Path("/{empNo}")
    @Produces({ MediaType.APPLICATION_JSON, MediaType.APPLICATION_XML })
    public void deleteEmployee(@PathParam("empNo") String empNo) {
        EmployeeDAO.deleteEmployee(empNo);
    }

}

URLs related to CRUD (Create, Read, Update, Delete) including:

Action	URI + Data (XML hoặc JSON)
Create (@POST)	/contextPath/servletPath/employees { "empNo":"E05", "empName":"Martin", "position":"Salesman" } <employee> <empNo>E05</empNo> <empName>Martin</empName> <position>Salesman</position> </employee>
Read (@GET)	/contextPath/servletPath/employees /contextPath/servletPath/employees/{empNo}
Update (@PUT)	/contextPath/servletPath/employees { "empNo":"E01", "empName":"Smith 2", "position":"Cleck" } <employee> <empNo>E01</empNo> <empName>Smith 2</empName> <position>Clerk</position> </employee>
Delete (@DELETE)	/contextPath/servletPath/employees/{empNo}