Strait Fram Singapuur

I am personally not impressed with what Windows 8 has to offer. In short here is the Summary:

• Responsive start and shut down time - more like Apple devices.
• Slider UIs copied from iPhone and similar mobile devices.
• Metro UI - It's boring over time and just gets in the way.
• Integrated App Store, create an app and sell it for 99 paise :) Finally Microsoft realized the power of developers.
• Notifications concept copied from Facebook. Blue Screen of Death gets makeover for Windows 8, I am not sure from wehere Microsoft copied “Blue Screen of Death”, any ideas guys?

Users come to you and shout "Why Trades page is taking too much time to load?" Now you may say because I call Trade Service so it might be taking time to return the response in timely fashion. You approach developer of the Service and ask - Can you please tell how much time is being taken for getTrades(userId) to return trades from database for XYZ user? Developer will say Yes I can - let me check you in the logs as I have put System.currentTimeMillis(); statements in my code as shown below:

Hi Today I got an email from roger.xia from China regarding the Sphinx search article i posted few months back, he requested the source code so I uploaded the same on dzone, Any one who is interested in trying Sphinx free text search code can download it from dzone site.


URL - http://java.dzone.com/articles/using-sphinx-and-java






---------------------------------------
Hi , Munish Gogna

I come from china , and i read your article about Sphinx, it was very useful for me, but i can't find the sample source code, can you send me a copy of the sample complete source code to me?
thank u very much !

best wishes.
roger.xia
20110822
---------------------------------------

This is what I would like to have in next release of Google+:
1. Robust developer API (Many users get hooked on games like Farmville, and that would not have been possible without the application platform Facebook provides).
2. 'Import Facebook contacts' functionality (otherwise killing Facebook will take years of user attrition)
3. Integration with other Google offerings like Docs so that I can share selected documents with my circles, Latitude integration etc.
4. Less white space in UI (some how Facebook screens look more elegant and eye catching to me)
5. Seamless integration with popular apps like Twitter at least.

I hope that these features except the second one should be ready by end of this Year and then I would definitely think of giving Google+ a Thumbs up !!!

cheers,
Munish Gogna

Most of times we find ourself in situations where the XML instance doesn't fully comply with the available Java types.

Let's define a near real world problem to understand this.

Problem: Need to process XML message coming from some XYZ source we don't have control on( the message format is shown below). As can be seen dob element has value as date of birth for Nikhil but is surrounded by brackets [ and ]. Now if we want to unmarshal this message to Person object than with this limitation we will have to declare dob as String and then provide some more methods to parse date every time we process this XML message.

So what should we do - declare dob as String?

Nikhil
[1986-08-27]

Answer is NO, we can use adapters, how? be patient ..

Let's first define our domain object

// members are public just to keep it short..
@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Person {

 @XmlElement
 public String name;

 @XmlElement
 @XmlJavaTypeAdapter(DateAdapter.class)
 public Date dob;

}

As can be seen above we have declared dob as of type Date only, but how it can be populated with the kind of values we are getting, you got it - yes it is our DateAdapter class who is going to manage this, let's see how:

/**
  * Our custom dob adapter.
  */
 class DateAdapter extends XmlAdapter<String, Date> {
  
  static SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");

  public DateAdapter() {
  }

  @Override
  public String marshal(Date date) throws Exception {
   // while sending message back to the source we will obey its format
   return "[" + format.format(date) + "]";
  }

  @Override
  public Date unmarshal(String dob) throws Exception {
   // remove unwanted characters and build date
   dob = dob.replace("[", "").replace("]", "");
   return format.parse(dob);
  }

 }

Let's unmarshal the message now:

JAXBContext context = JAXBContext.newInstance(Person.class);
  Unmarshaller unmarshal = context.createUnmarshaller();
// employee file is the source of message in this example
  Person person = (Person) unmarshal.unmarshal(new File("employee"));

  Assert.assertEquals("Nikhil", person.name);
  Assert.assertEquals("Wed Aug 27 00:00:00 SGT 1986", person.dob
    .toString());

and marshalling our new Person object works fine too :)

Person person = new Person();
  person.name="Toshi";
  person.dob= format.parse("2010-10-10");
  
  Marshaller marshaller = context.createMarshaller();
  marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
  marshaller.marshal(person, System.out);
// The console output is shown below:

  
      Toshi
      [2010-10-10]
  

This is exactly what we expect, value of dob within brackets. This was just a simple example to demonstrate the power of adapters for handling alien types in Java XML world. Hope you can also use this approach in some of your Projects.

See you later !!!

This post is dedicated to my friend jagdish salgotra who wanted me to write something on RESTful web services and to all starters in this area.

In the REST(REpresentational State Transfer) world, information on the server side is considered a resource, which anyone can access in a uniform way using web URIs (Uniform Resource Identifiers) and HTTP. Because REST uses HTTP as the communication protocol, the REST style is constrained to a stateless client/server architecture. We can map the HTTP methods POST, GET, PUT, and DELETE to create, read, update and delete (CRUD) operations.

There are many ways to write RESTful web services:
> Sun offers a reference implementation for JAX-RS code-named Jersey.
> Spring provides RestTemplate for the same purpose

In this sample example (very basic and naive just to give u all a gentle kick) I will try to explain how we can use DEPARTMENT as representational state in REST using GET method. We will try to map following urls to the particular state we are interested in using Jersey implementation.

/api/departments/	Get all departments
/api/departments/{id}	Get details of a particular department
/api/departments/employees	Get all departments with employee details
/api/departments/{id}/employees	Get employees of particular department

NOTE: All employees related data will be available under department node (by design)

The output of the Restful web services can be a plain text, html, xml, json or any media type, For our example We will use XML as content type of our service output and will rely on JAXB annotations to provide the required marshaling/unmarshaling services.

Let's start with the root XML element. I chose to call mine GetDepartmentResponse, and use it as a container for a collection of Department objects. This is just to do with the convention I usually follow (no hard fast rules behind this).

package com.mg.rest.hr.resources;

import java.util.ArrayList;
import java.util.List;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class GetDepartmentResponse {

 private List<Department> departments;

 @XmlElement(name = "department")
@XmlElementWrapper(name = "departments")
 public List<Department> getAllDepartments() {
  if (departments == null) {
   departments = new ArrayList<Department>();
  }
  return departments;
 }

}

Notice the @XmlElementWrapper annotation on the Department collection. This makes JAXB wrap all of the department XML elements inside of an departments XML element. Also notice that I placed the @XmlElement annotations on the getter methods instead of on the private fields. When placed on the private fields, JAXB will give you an error unless you add @XmlAccessorType(XmlAccessType.FIELD) at the class level.

Next we define our Resources - Department and Employee

package com.mg.rest.hr.resources;

import java.util.List;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlElementWrapper;
import javax.xml.bind.annotation.XmlType;

/**
 * 
 * @author Munish Gogna
 *
 */
@XmlType(name = "department")
public class Department {

 private String deptId;
 private String deptName;
 private List<Employee> employees;

 public Department() {
 }

 @XmlElement
 public String getDeptId() {
  return deptId;
 }

 @XmlElement(name = "employee")
 @XmlElementWrapper(name = "employees")
 public List<Employee> getEmployees() {
  return employees;
 }

 @XmlElement
 public String getDeptName() {
  return deptName;
 }

 public void setDeptId(String deptId) {
  this.deptId = deptId;
 }

 public void setEmployees(List<Employee> employees) {
  this.employees = employees;
 }

 public void setDeptName(String deptName) {
  this.deptName = deptName;
 }

}

In the example above, we use @XmlType at the class level instead of @XmlRootElement because it is not the root element

package com.mg.rest.hr.resources;

import java.math.BigDecimal;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlType;

/**
 * 
 * @author Munish Gogna
 * 
 */
@XmlType(propOrder = { "empId", "empName", "salary" })
public class Employee {

 private String empId;
 private String empName;
 private BigDecimal salary;

 public Employee() {
 }

 public Employee(String empId, String empName, BigDecimal salary) {
  super();
  this.empId = empId;
  this.empName = empName;
  this.salary = salary;
 }

 @XmlElement
 public BigDecimal getSalary() {
  return salary;
 }

 @XmlElement
 public String getEmpId() {
  return empId;
 }

 @XmlElement
 public String getEmpName() {
  return empName;
 }

 public void setEmpId(String empId) {
  this.empId = empId;
 }

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

 public void setSalary(BigDecimal salary) {
  this.salary = salary;
 }

}

Now lets create a JAX-RS RESTful web service that can return above defined object graph in the responses we have defined in the beginning of this article.

JAX-RS defines a resource as any Java class (POJO) that uses JAX-RS annotations to implement a web resource. The annotation @Path identifies a Java class as a resource class as shown below.

package com.mg.rest.hr;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.PathParam;
import javax.ws.rs.Produces;

import com.mg.rest.hr.resources.Department;
import com.mg.rest.hr.resources.GetDepartmentResponse;

/**
 * Service to handle Department and related resources.
 * Just a mock implementation, nothing fancy.
 * @author Munish Gogna
 *
 */
@Path("/api")
public class DepartmentResource {

 @GET
 @Produces("text/xml")
 @Path("/departments/employees")
 public GetDepartmentResponse getAllDepartmentsWithEmployees() {
  GetDepartmentResponse response = new GetDepartmentResponse();
  response.getAllDepartments().addAll(
    FromHeaven.getDeptsWithEmps().values());
  return response;
 }

 @GET
 @Produces("text/xml")
 @Path("/departments/{id}")
 public GetDepartmentResponse getDepartment(@PathParam("id") String id) {
  GetDepartmentResponse response = new GetDepartmentResponse();
  Department dept = FromHeaven.getDepts().get(id);
  response.getAllDepartments().add(dept);
  return response;
 }

 @GET
 @Produces("text/xml")
 @Path("/departments/{id}/employees")
 public GetDepartmentResponse getEmployeesForDepartment(
   @PathParam("id") String id) {
  GetDepartmentResponse response = new GetDepartmentResponse();
  Department dept = FromHeaven.getDeptsWithEmps().get(id);
  response.getAllDepartments().add(dept);
  return response;

 }

 @GET
 @Produces("text/xml")
 @Path("/departments")
 public GetDepartmentResponse getAllDepartments() {
  GetDepartmentResponse response = new GetDepartmentResponse();
  response.getAllDepartments().addAll(FromHeaven.getDepts().values());
  return response;

 }
}

Notice the @Produces("text/xml") annotation, and that the method returns a GetDepartmentResponse object. Since the GetDepartmentResponse is annotated with JAXB annotations, JAX-RS will automatically marshal the response to XML.
Also note that FromHeaven is a utility class that provides dummy departmental data(This class has 2 hard coded departments D1 and D2 with 2 employees in D1 and only single employee in D2)

Let's try some URIs now:

1. http://localhost:8080/rest/api/departments

 
  
   D2
   Human Resource
  
  
   D1
   Finance
  
 

2. http://localhost:8080/rest/api/departments/D1

 
  
   D1
   Finance
  
 

3. http://localhost:8080/rest/api/departments/employees

 
  
   D1
   Finance
   
    
     e1
     Munish Gogna
     1000
    
    
     e2
     Jagdish Salgotra
     2000
    
   
  
  
   D2
   Human Resource
   
    
     e3
     Sahil Gogna
     5000
    
   
  
 

4.http://localhost:8080/rest/api/departments/D1/employees

 
  
   D1
   Finance
   
    
     e1
     Munish Gogna
     1000
    
    
     e2
     Jagdish Salgotra
     2000
    
   
  
 

In order for Jersey to work, we need to configure the JAX-RS Servlet in the web.xml as shown below:

 
  com.mg.rest.hr
  JAX-RS REST Servlet
  com.sun.jersey.spi.container.servlet.ServletContainer
  
   com.sun.jersey.config.property.packagescom.mg.rest.hr
  1
 
 
  JAX-RS REST Servlet
  /*
 

Notice that we have to provide the package name (com.mg.rest.hr) of the resource handler classes to the servlet class.

That's all for now, later some day we will try make these RESTful services secure so that only authorized callers can use these resources.

Please don't forget to provide your valuable feedback, especially you Jagi :)

First of all nothing very fancy or technical about this post :)

Let's say you have an enum declaration as shown below and you want to store these values as String (not the evil ordinals) in the database:

public enum UserSex {
 MALE, FEMALE, UNKNOWN
}

To save this enum as String in database, the table where this enum is referenced should declare a column of type varchar as shown below:

`user_sex` varchar(255) DEFAULT NULL

The entity (say User) should use this enumeration as shown below:

@Entity
@Table(name = "user")
public class User {

private Integer id;
private UserSex userSex;

@Id
public Integer getId() {
 return id;
}

@Enumerated(EnumType.STRING)
 @Column(name ="user_sex")
 public UserSex getUserSex() {
  return userSex;
 }

 public void setId(Integer id) {
  this.id = id;
 } 

 public void setUserSex(UserSex userSex) {
  this.userSex = userSex;
 }

That's all. Now if you want to load all MALE users, you can use this column in JPA queries as

public List<User> getAllMaleUsers() {
  return entityManager.createQuery(
    "select user from User as user where user.userSex=:userSex")
    .setParameter("userSex", UserSex.MALE).getResultList();
 }

Please note that this will work only in case you have complete control on the database side, in case the column is declared as integer or varchar having length say 1 then you will have to write your own converter or fall back to evil ordinal().

NOTE: I'm guessing but I'm pretty sure that for using ENUM as String hibernate 3.2+ is required. So if anyone out there is interested in knowing my POM dependencies then here are they (specific to JBOSS AS 5.1.0 deployment)

   
javaee
   javaee-api
   5
   compile
  
  

   javax.persistence
   ejb3-persistence
   1.0
   provided
  
  
   org.hibernate
   hibernate-entitymanager
   3.3.1.ga
   
    
     javax.persistence
     persistence-api
    
    
     jboss
     jboss-common-core
    
    
     jboss
     javassist
    
   
  

Hi everyone, First of all thanks to Anna Hazare and all who have really fought for lokpal bill.

Today's article is about sending Thanks email to Anna Hazare for his tremendous dedication towards our great nation, it's about setting up SMTP server to send emails from your application hosted on JBOSS Application server.


The focus will be on the Anna Hazare and Jboss setup rather than providing a full fledged Email Service.


Our application will be sending emails over gmail SMTP server.
Please pay attention to comments from now onwards through out this article. :)

Maven dependency : Here is a skelton of our maven project.

 4.0.0
 com.mg.poc.email
 JbossMail
 0.0.1-SNAPSHOT
 ejb
 A Simple project to send Emails using Gmail (service running in JBOSS) 

 
  
   Munish Gogna
   gognamunish@gmail.com
   www.twitter.com\munishgogna
  
 

 
 
  
   javaee
   javaee-api
   5
   provided
  

 
 

  ${basedir}/src
  
   
    ${basedir}/src
    
     **/*.java
    
   
  
  
   
    org.apache.maven.plugins
    maven-ejb-plugin
    
     3.0
    
   
   
    maven-compiler-plugin
    
     1.5
     1.5
    
   
  
 

STEP 1 Define our Gmail based SMTP mail service that we will use in our sample application.

SERVER\deploy\mail-service.xml : Create the service definition as shown below:

  
  
  

  
    java:/GMail
    gognamunish@gmail.com
    
    XXXXXX
    
      
       
            
            
      
      
      
            
            
         
    
    jboss:service=Naming
  

After placing this file in deploy folder, you should see following logs in server.log
15:40:49,985 INFO [MailService] Mail Service bound to java:/GMail

STEP 2 Let's build our sample EJB based application that will consume this service to send emails, time to define our remote interface.

package com.mg.poc.email;

import javax.ejb.Remote;

/**
 * Simple interface for our Mail Service.
 * 
 * @author Munish Gogna
 * 
 */
@Remote
public interface MailSender {

 /**
  * Sends mail using GMAIL Service.
  * 
  * @param envelope
  *            envelope to send
  */
 void sendMail(MailEnvelope envelope) throws GmailException;

}

The Envelope class is a simple class that holds regular stuff we need to send email. It is defined as :

package com.mg.poc.email;

import java.io.Serializable;

/**
 * Contains regular email stuff (with some defaults).
 * 
 * @author Munish Gogna
 *
 */
public class MailEnvelope implements Serializable {

 private static final long serialVersionUID = 1L;
    
 private String subject ="thanks Anna Hazare";
 private String to;
 private String from ="gognamunish@gmail.com";
 private String body ="Anna you are great. We the people of india have won the 1st step against the Govt. & feeling real freedom only Bcoz of you. - love you !!!!";

 /** setters/getters omitted */

}

Now as we have defined the interface for our Email Service, let's provide the implementation of the same.

package com.mg.poc.email;

import javax.annotation.Resource;
import javax.ejb.Stateless;
import javax.mail.Address;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.Message.RecipientType;
import javax.mail.internet.AddressException;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;

/**
 * Bean to manage simple email functionality.
 * 
 * @author Munish Gogna
 * 
 */
@Stateless
public class MailService implements MailSender {

 /**
  * This resource is defined in mail-service.xml file.
  */
 @Resource(mappedName = "java:/GMail", description = "jndi mapping for our simple mail service")
 Session mailSession;

 public void sendMail(MailEnvelope envelope) throws GmailException {
  
  if(envelope == null){
   throw new GmailException("envelope is null");
  }
  
  Message simpleMessage = new MimeMessage(mailSession);

  try {
   simpleMessage.setFrom(createInternetAddress(envelope.getFrom()));
   simpleMessage.setRecipient(RecipientType.TO, createInternetAddress(envelope.getTo()));
   simpleMessage.setSubject(envelope.getSubject());
   simpleMessage.setText(envelope.getBody());

   Transport.send(simpleMessage);
  } catch (MessagingException e) {
   throw new GmailException(e.getMessage());
  }

 }

 private Address createInternetAddress(String address) throws GmailException {
  try {
   return new InternetAddress(address);
  }catch (AddressException e) {
   throw new GmailException(e.getMessage());
  }
 }

}

That's all we are done.
> Generate jar - mvn clean install
> copy JbossMail-0.0.1-SNAPSHOT.jar to deploy folder.
> server logs should show binding of our EJB Stateless session beans as shown below:

15:41:33,403 INFO [EJBContainer] STARTED EJB: com.mg.poc.email.MailService ejbName: MailService
15:41:33,412 INFO [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI:

MailService/remote - EJB3.x Default Remote Business Interface


Finally we will test the service to make sure it actually sends email.

package com.mg.poc.email.test;

import java.util.Properties;

import javax.naming.Context;
import javax.naming.InitialContext;

import com.mg.poc.email.MailEnvelope;
import com.mg.poc.email.MailSender;

/**
 * Simple Test.
 * 
 * @author Munish Gogna
 * 
 */
public class TestMail {

 public static void main(String[] args) throws Exception {
  Properties properties = new Properties();

  properties.put("java.naming.factory.initial",
    "org.jnp.interfaces.NamingContextFactory");
  properties.put("java.naming.factory.url.pkgs",
    "org.jboss.naming:org.jnp.interfaces");
  properties.put("java.naming.provider.url", "localhost");
  Context context;
  try {
   context = new InitialContext(properties);
   MailSender beanRemote = (MailSender) context
     .lookup("java:MailService/remote");

   MailEnvelope envelope = new MailEnvelope();
   envelope.setTo("anna.hazare@gmail.com");

   beanRemote.sendMail(envelope);
   System.out.println("mail sent successfully !!!");
  } catch (Exception e) {
   e.printStackTrace();
  }
 }
}

Note : In case you want to run this client, make sure you add all the required client libraries in the classpath, do one thing add all jars in JBOSS_HOME/client folder to classpath OR try adding following dependency in the pom file.

jboss
jbossall-client
${jboss.version}
${jboss.home}/client/jbossall-client.jar
system

Creating client jars and managing dependencies\jndi lookups can be nightmare sometimes, not some times but most of the times, please do share your thoughts on the same.

To end discussion on this topic I would once again like to thank everyone who stood with Hazare to fight against corruption.

Thanks.

Few days back I came across Spring social API library developed to access social networking sites from within the Java programs and finally Today I got chance to explore it :)

The current milestone includes templates for Twitter, Facebook and LinkedIn. These templates provide an easy way to access each social networking site and make integrating with those sites relatively straight forward. Each of these templates extend Spring's RestTemplate which is a generic template for accessing REST based web services. All hard core fans of Spring's JDBCTemplate and HibernateTemplate will love this.

To use Spring social:
1. Set up developer account with target social networking site.
2. Request an OAuth token from the target social networking site for each new user.
3. Use the right Spring Source template (e.g TwitterTemplate), passing in the developer keys (ApiKey and ApiSecret) as well as OAuth key for the current user.
4. Thats all :)

Once authorized, the application code required to access any given social site is very easy, so easy that even MBA guy can do it!

Check it out:

//Get Twitter template
TwitterTemplate twitter = new TwitterTemplate(apiKey, apiSecret, accessToken, accessTokenSecret);
twitter.updateStatus("Hey, I'm tweeting with #Spring Social! wow");

//Get Facebbook template
FacebookTemplate facebook = new FacebookTemplate(accessToken);
facebook.updateStatus("Hey, I'm posting with #Spring Social! wow");

//Get LinkedIn template
LinkedInTemplate template = new LinkedInTemplate(apiKey, apiSecret, accessToken, accessTokenSecret);
List <linkedinprofile> connections = template.getConnections(); 

The OAuth authorization part is not as clean as I would have liked. SpringSource has created a reference implementation called Greenhouse to demonstrate how to use the API.

Don't know what is OAuth?
So what is up with this OAuth. In just a few words, it is an authentication service. As an application you forward a visitor to the authentication service. The visitor authenticates itself and your application receives the result using a callback. If the result is positive, the visitor has authorized your application to act on the behalf of the visitor. That way you can use services of the provider without knowing who you are dealing with. It is also possible to store the provided authentication for future use (Greenhouse has this featute).

However we can also use some other OAuth libraries to avoid complexities in GreenHouse API and then just use the REST-like APIs of each service by directly manipulating URLs. The most interesting, easy to use and simple I found is Scribe, its a cool API that provides support for Facebook, Google ,Yahoo, LinkedIn, Twitter, Foursquare, Evernote, Vimeo and Yammer.

The latest version is 1.0.9 that should include Facebook API (as per GitHub), as of now this change is not available for 1.0.9 version in maven, I built it manually getting source from github repository.
You can pull scribe from a maven repository, just add this to your pom.xml file.

org.scribe
scribe
1.0.9

Now its time to create the OAuthService object
The OAuthService is the one you use to sign your requests. You create it using Scribe’s ServiceBuilder like shown below.

You can use the Facebook 'SpringSocialAPI' app that I created, details are:
Application ID: 175348469171013
Application Secret: c3301704fdd6da30b5b8ab68f9808b09

String apiKey = "c97dc03050b89baf893347f40f177d55";
    String apiSecret = "c3301704fdd6da30b5b8ab68f9808b09";
    OAuthService service = new ServiceBuilder()
                                  .provider(FacebookApi.class)
                                  .apiKey(apiKey)
                                  .apiSecret(apiSecret)
                                  .callback("http://localhost:8080/social/callback.jsp")
                                  .build();

The token will be generated and will be available on the mentioned callback url.

You need to get a request token, like this:
Token requestToken = service.getRequestToken();
String your_token = requestToken.getToken();

Now go authorize it! for this make a request to the authorize url (this varies between apis).
For Facebook this is it: https://graph.facebook.com/me?oauth_token=YOUR_TOKEN_HERE

Thanks, see u soon!!!

• Joint Account – Account having multiple owners.
• Cash Account: The basic account where you deposit cash to buy stocks, bonds, mutual funds, etc. 
• Margin Account: - Margin basically allows you to borrow from your broker against the cash and securities in your account. Profits can diminish quickly when you use margin, so be very careful!
• Forex Account etc.

• A market order is an order to buy or sell immediately at the best available price. These orders do not guarantee a price, but they do guarantee the order's immediate execution. Typically, if you are going to buy a stock, then you will pay a price near the posted ask. If you are going to sell a stock, you will receive a price near the posted bid. 
• A limit order sets the maximum or minimum price at which you are willing to buy or sell. For example, if you wanted to buy a stock at $10, you could enter a limit order for this amount. This means that you would not pay a penny over $10 for the particular stock. It is still possible, however, that you buy it for less than the $10.

Source- wikipedia & encyclopedia