REST API for Employees with jQuery Client

• http://localhost:8888/hrservice/webresources/employees/id
  It takes an employee id as path parameter and provides a single JSON object that contains information about employee with id

• http://localhost:8888/hrservice/webresources/employees
  It provides an array of JSON objects where each object contains information about an employee

Creating RESTful Service

1. Start NetBeans and create a new web project with name hrservice
2. Add ojdbc6.jar (Oracle JDBC Driver) to libraries node of the project as we use Oracle Database
3. Select hrservice project in Projects tab. Use right click to bring popup menu and select New->Other. Select Web Services in Category and RESTful Web Servies from Patterns in File Types
4. Select Simple Root Resource in Select Pattern step
5. Enter the following details in the next screen as shown in the screenshot
   

6. Netbeans creates two files - ApplicationConfig.java and EmployeesResource.java
7. ApplicationConfig.java is used to route urls to classes. It contains @ApplicationPath annotation to specify path that is associated with RESTful services. It also registers classes that are to be considered for routing

   package rest;
   
   import java.util.Set;
   import javax.ws.rs.core.Application;
   @javax.ws.rs.ApplicationPath("webresources")
   public class ApplicationConfig extends Application {
       @Override
       public Set<Class<?>> getClasses() {
           Set<Class<?>> resources = new java.util.HashSet<>();
           addRestResourceClasses(resources);
           return resources;
       }
       private void addRestResourceClasses(Set<Class<?>> resources) {
           resources.add(rest.EmployeesResource.class);
       }
   }
   

8. Modify EmployeesResource.java as follows. @Path annotation is used to map URL pattern to Restful service. @Path annotation can be given for a method to further add path parameters.  @PathParam is used to copy path parameter to method parameter.

   package rest;
   import java.sql.SQLException;
   import java.util.ArrayList;
   import java.util.List;
   import javax.sql.rowset.CachedRowSet;
   import javax.ws.rs.PathParam;
   import javax.ws.rs.Produces;
   import javax.ws.rs.GET;
   import javax.ws.rs.Path;
   import javax.ws.rs.WebApplicationException;
   import javax.ws.rs.core.Response;
   import oracle.jdbc.rowset.OracleCachedRowSet;
   
   @Path("employees")
   public class EmployeesResource {
       // use this method when URL is /employees
       @GET
       @Produces("application/json")
       public List<Employee> getEmployees()  {
           try {     
               CachedRowSet crs = new OracleCachedRowSet();
               crs.setUrl("jdbc:oracle:thin:@localhost:1521:XE");
               crs.setUsername("hr");
               crs.setPassword("hr");
               crs.setCommand("select * from employees");
               crs.execute();
               ArrayList<Employee> emps = new ArrayList<>();
               while(crs.next()) {
                   Employee  e  = new Employee();
                   e.setName( crs.getString("first_name"));
                   e.setSalary( crs.getInt("salary"));
                   emps.add(e);
               }
               return emps;
         }
         catch(Exception ex) {
             throw new WebApplicationException(Response.Status.INTERNAL_SERVER_ERROR);
         }
       } // getEmployees()
       
       @Path("{id}")   // use this method when URL contains id also (employees/id) 
       @GET
       @Produces("application/json")
       public Employee getEmployee( @PathParam("id") int id)  {
         try {     
               CachedRowSet crs = new OracleCachedRowSet();
               crs.setUrl("jdbc:oracle:thin:@localhost:1521:XE");
               crs.setUsername("hr");
               crs.setPassword("hr");
               crs.setCommand("select * from employees where employee_id = ?");
               crs.setInt(1,id);
               crs.execute();
               if (crs.next()) {
                   Employee  e  = new Employee();
                   e.setName( crs.getString("first_name"));
                   e.setSalary( crs.getInt("salary"));
                   return e;
               }
               else
                   throw new WebApplicationException(Response.Status.NOT_FOUND); //employee not found so send 404 to client 
         }
         catch(SQLException ex) {
            throw new WebApplicationException(Response.Status.INTERNAL_SERVER_ERROR); //Some exception on server, so send 500 to client
         }
       } // getEmployee()
   }
           

Creating jQuery Client

listemployees.html

<!DOCTYPE html>
<html>
    <head>
        <title>List of Employees</title>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <script src="jquery-2.1.4.js" type="text/javascript"></script>
        <script>
            $(function () {
                $.ajax("http://localhost:8888/restdemo/rest/employees",
                   {
                       success: showResult,  // call on success
                       error: showError      // call on error 
                   }
               );
            }
            );
            // parameter is an array of Javascript objects  
            function showResult(employees) {
                var output = "";
                $.each(employees,
                    function (idx, emp) {
                        output += "<li>" + emp.name + "," + emp.salary + "</li>";
                    }
                );
                $("#details").html(output);
            }
            
            function showError(xhr) {
                alert("Sorry! Error on server!");
            }
        </script>
    </head>
    <body>
        <h2>List of Employees</h2>
        <ul id="details">
        </ul>
    </body>
</html>

empclient.html

<!DOCTYPE html>
<html>
    <head>
        <title>Employee Client</title>
        <script src="jquery-2.1.4.js" type="text/javascript"></script>
        <script>
            function getDetails() {
                $.ajax("http://localhost:8888/restdemo/rest/employees/" + $("#empid").val(),
                        {
                            success: showResult,  // call on success
                            error: showError      // call on error
                        }
                );
            }

            function showResult(emp) {
                $("#details").html(emp.name + "," + emp.salary);
            }

            function showError(xhr) {
                if (xhr.status === 404) 
                    $("#details").html("Employee not found!");
                else
                    if (xhr.status === 500)
                        $("#details").html("Server Error!");
            }


        </script>
    </head>
    <body>
        <h2>Employee Information </h2>
        Employee Id : <input type="text" id="empid" />
        <p/>
        <button onclick="getDetails()">Get Details</button>
        <p/>
        <h2 id="details"></h2>


    </body>
</html>