Book Review: Murach’s HTML5 and CSS3, 3rd Edition

Murach’s HTML5 and CSS3, 3rd Edition is a one stop solution to solve all your learning requirements for developing the front end of your applications.

The books starts with introduction to HTML and CSS and quickly covers some advanced topics in it like Responsive web design, adding audio and video, using CSS3 features to name a few. The chapter on responsive web design is very useful as it covers concepts really relevant in today’s multi screen world.

The book also covers concepts on Javascript and the famous jQuery library including jQuery Mobile. The chapters on designing and deploying websites are very useful for those who have done development but never got it live to the outside world. If the book could include some suggestions for good hosting providers and good domain name service provider then it would have been very useful.

As is the norm with Murach’s books, this book is also a highly practical oriented book with all the concepts explained via examples. Ideally I would use this book as a reference and read those parts of the book as and when necessary. The chapter on Responsive web design is highly recommended as I am not aware of such an elaborate coverage of the topic else where.

Setting up sharded mongodb cluster in localhost

I have been playing around with MongoDb, thanks to the M101J Course offered by Mongodb University. These NoSQL datastores are gaining popularity due to a number of reasons and one among them being the ease with which they can be scaled out i.e horizontal scaling. This horizontal scaling in MongoDB can be achieved by creating a sharded cluster of mongodb instances.

You might want to understand the concept of sharding before continuing. The MongoDB reference has a very clear explanation for the same here.
Continue reading Setting up sharded mongodb cluster in localhost

Getting rid of Getters and Setters in your POJO

We all have read in Java books about encapsulation of fields in Java class and also when ever you code you are asked to take special care in encapsulating the fields and providing explicit Getters and Setters. And these are very strict instructions. Lets step back a bit and find out the reason behind encapsulating the fields. Its all done to have a control over the access and modification of the fields. One might want to allow the user of the class to access data from only few fields or control the update of data of the fields in the class and so on. And on other occassions the frameworks would need these getters and setters to populate your POJOs(Plain Old Java Objects).

Now the pain involved in adding these getters and setters is quite a bit and this pain has been reduced by the IDEs which allow you to generate the getters and setters for the fields. But these generated code make your class definition very verbose and hide the actual business logic, if any, which you might have it inside the class definition. There have been lot of ways by which you can get away with defining the getters and setters explicitly and I have even blogged about using Project Lombok to use annotations to declare the getters and setters. I have come across another approach to avoid defining the getters and setters and this approach doesn’t even auto generate the code or use annotations to define them. I am sure I have read this approach somewhere but unable to recall, so its something which has been used and I am trying to create an awareness among my readers about this approach via this blog post.

Let me first define the class with the getters and setters and then show how to get rid of them

class TaskWithGettersSetters {
  public TaskWithGettersSetters(String title, String notes,
      LocalDateTime deadline, String assignedTo) {
    this.title = title;
    this.notes = notes;
    this.addedOn = LocalDateTime.now();
    this.deadline = deadline;
    this.assignedTo = assignedTo;
  }

  public TaskWithGettersSetters() {
  }

  private String        title;
  private String        notes;
  private LocalDateTime addedOn;
  private LocalDateTime deadline;
  private String        assignedTo;

  public String getTitle() {
    return title;
  }

  public void setTitle(String title) {
    this.title = title;
  }

  public String getNotes() {
    return notes;
  }

  public void setNotes(String notes) {
    this.notes = notes;
  }

  public LocalDateTime getAddedOn() {
    return addedOn;
  }

  public void setAddedOn(LocalDateTime addedOn) {
    this.addedOn = addedOn;
  }

  public LocalDateTime getDeadline() {
    return deadline;
  }

  public void setDeadline(LocalDateTime deadline) {
    this.deadline = deadline;
  }

  public String getAssignedTo() {
    return assignedTo;
  }

  public void setAssignedTo(String assignedTo) {
    this.assignedTo = assignedTo;
  }

}

There is nothing to explain in the above code, pretty clear with fields being private and public getters and setters. The class definition is about 60 lines. Let see how we can define class without providing getters and setters:

class Task {

  public Task(String title, String notes, LocalDateTime deadline,
      String assignedTo) {
    this.title = title;
    this.notes = notes;
    this.addedOn = LocalDateTime.now();
    this.deadline = deadline;
    this.assignedTo = assignedTo;
  }

  public final String        title;
  public final String        notes;
  public final LocalDateTime addedOn;
  public final LocalDateTime deadline;
  public final String        assignedTo;

}

The above is what I call class definition on diet:) It is less verbose and is just 18 lines. You must be scared looking at the public modifiers for the fields and also confused looking at the final modifiers to the field. Let me explain the ideology behind this approach:

  1. As the fields are final they cannot be modified after initialized so we need not worry about the scare of data in the field getting modified. And we have to provide a constructor which will initialize these fields, otherwise compiler will shout at you for not understanding what final modifier is.
  2. The data in the fields can be accessed by using the fields directly and not via the getter methods.
  3. This approach enforces immutability of objects i.e if we have to update the field we have to create a new object with the updated value of the field.

Now having Immutable objects provides lots of advantages few of them being:

  • Writing concurrent code is quite easy because we need not worry about getting locks on the object as we are never going to modify the object, we can just read the object data and cannot modify due to the use of final.
  • Immutable objects leads to having lot of short lived objects which helps in reducing the GC overhead involved in managing long lived objects and objects with lot of live references.

We can even provide a factory method for creating instances of Task. Lets see the above class in action:

import java.time.LocalDateTime;

public class GettingRidOfGettersSettersDemo {
  public static void main(String[] args) {
    //One can make use of Factory method to initialize the data
    Task task1 = new Task("Task 1", "some notes", LocalDateTime.now().plusDays(5), "sana");
    //Very clean approach to access the field data - no getYYY() noise 
    System.out.println(task1.title + " assigned to " + task1.assignedTo);
    Task task2  = new Task("Task 2", "some notes", LocalDateTime.now().plusDays(6), "raj");
    System.out.println(task2.title + " assigned to " + task2.assignedTo);
  }
}

Update:
Thanks a lot for the comments and your thoughts both here and on DZone. I spent some time in identifying how one can work without the need for getters and setters in scenarios mentioned where without getters and setters its not possible. One such scenario is marsalling and unmarshalling of JSON and another scenario is where we have a List of some values as property and we need to give an read only access to the users of the object. The below are examples of using POJOs without getters and setters in JSON marshalling and unmarshalling using GSON and Jackson JSON libraries:

The below is the code for using GSON JSON Library:

public class GsonParserDemo {

  public static void main(String[] args) {
    HashMap<String, Object> jsonData = new HashMap<String, Object>();
    jsonData.put("name", "sanaulla");
    jsonData.put("place", "bangalore");
    jsonData.put("interests", Arrays.asList("blogging", "coding"));
    Gson gson = new Gson();

    String jsonString = gson.toJson(jsonData);
    System.out.println("From Map: " + jsonString);
    

    Person person = gson.fromJson(jsonString, Person.class);
    
    System.out.println("From Person.class: " + gson.toJson(person));
  }

  class Person {
    public final String name;
    public final String place;
    private final List<String> interests;

    public Person(String name, String place, List<String> interests) {
      this.name = name;
      this.place = place;
      this.interests = interests;
    }
 
    public List<String> interests(){
      return Collections.unmodifiableList(interests);
    }
  }
}

The output of above code is:

From Map: {"name":"sanaulla","place":"bangalore","interests":["blogging","coding"]}
From Person.class: {"name":"sanaulla","place":"bangalore","interests":["blogging","coding"]}

To note : GSON doesn’t use constructor nor getters and setters to map JSON to Java class.

The below is the code for using Jackson JSON Library:

public class JacksonParserDemo {
  public static void main(String[] args) throws JsonGenerationException,
      JsonMappingException, IOException {
    HashMap<String, String> jsonData = new HashMap<String, String>();
    jsonData.put("name", "sanaulla");
    jsonData.put("place", "bangalore");

    ObjectMapper objectMapper = new ObjectMapper();

    String jsonString = objectMapper.writeValueAsString(jsonData);
    System.out.println("Json from map : " + jsonString);

    Person person = objectMapper.readValue(jsonString, Person.class);
    System.out.println("Json from Person : "
        + objectMapper.writeValueAsString(person));
  }

}
class Person {
  
  public final String name;
  
  public final String place;

  @JsonCreator
  public Person(@JsonProperty("name") String name,
      @JsonProperty("place") String place) {
    this.name = name;
    this.place = place;
  }

}

The output of the above code is:

Json from map : {"name":"sanaulla","place":"bangalore"}
Json from Person : {"name":"sanaulla","place":"bangalore"}

I am investigating some concerns raised about Object Relational Mappers and the Joda Time.

Using Google Guava Cache for local caching

Lot of times we would have to fetch the data from a database or another webservice or load it from file system. In cases where it involves a network call there would be inherent network latencies, network bandwidth limitations. One of the approaches to overcome this is to have a cache local to the application.

If your application spans across multiple nodes then the cache will be local to each node causing inherent data inconsistency. This data inconsistency can be traded off for better throughput and lower latencies. But sometimes if the data inconsistency makes a significant difference then one can reduce the ttl (time to live) for the cache object thereby reducing the duration for which the data inconsistency can occur.

Among a number of approaches of implementing local cache, one which I have used in a high load environment is Guava cache. We used guava cache to serve 80,000+ requests per second. And the 90th percentile of the latencies were ~5ms. This helped us scale with the limited network bandwidth requirements.

In this post I will show how one can add a layer of Guava cache in order to avoid frequent network calls. For this I have picked a very simple example of fetching details of a book given its ISBN using the Google Books API.

A sample request for fetching book details using ISBN13 string is:
https://www.googleapis.com/books/v1/volumes?q=isbn:9781449370770&key={API_KEY}

The part of response which is useful for us looks like:
SampleResponse

A very detailed explanation on the features of Guava Cache can be found here. In this example I would be using a LoadingCache. The LoadingCache takes in a block of code which it uses to load the data into the cache for missing key. So when you do a get on cache with an non existent key, the LoadingCache will fetch the data using the CacheLoader and set it in cache and return it to the caller.

Lets now look at the model classes we would need for representing the book details:

  • Book class
  • Author class

The Book class is defined as:
[java]
//Book.java
package info.sanaulla.model;

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

public class Book {
private String isbn13;
private List<Author> authors;
private String publisher;
private String title;
private String summary;
private Integer pageCount;
private String publishedDate;

public String getIsbn13() {
return isbn13;
}

public void setIsbn13(String isbn13) {
this.isbn13 = isbn13;
}

public List<Author> getAuthors() {
return authors;
}

public void setAuthors(List<Author> authors) {
this.authors = authors;
}

public String getPublisher() {
return publisher;
}

public void setPublisher(String publisher) {
this.publisher = publisher;
}

public String getTitle() {
return title;
}

public void setTitle(String title) {
this.title = title;
}

public String getSummary() {
return summary;
}

public void setSummary(String summary) {
this.summary = summary;
}

public void addAuthor(Author author){
if ( authors == null ){
authors = new ArrayList<Author>();
}
authors.add(author);
}

public Integer getPageCount() {
return pageCount;
}

public void setPageCount(Integer pageCount) {
this.pageCount = pageCount;
}

public String getPublishedDate() {
return publishedDate;
}

public void setPublishedDate(String publishedDate) {
this.publishedDate = publishedDate;
}
}
[/java]

And the Author class is defined as:

[java]
//Author.java
package info.sanaulla.model;

public class Author {

private String name;

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}
[/java]

Lets now define a service which will fetch the data from the Google Books REST API and call it as BookService. This service does the following:

  1. Fetch the HTTP Response from the REST API.
  2. Using Jackson’s ObjectMapper to parse the JSON into a Map.
  3. Fetch relevant information from the Map obtained in step-2.

I have extracted out few operations from the BookService into an Util class namely:

  1. Reading the application.properties file which contains the Google Books API Key (I haven’t committed this file to git repository. But one can add this file in their src/main/resources folder and name that file as application.properties and the Util API will be able to read it for you)
  2. Making an HTTP request to REST API and returning the JSON response.

The below is how the Util class is defined:
[java language=”collapse”]
//Util.java

package info.sanaulla;

import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.ProtocolException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;

public class Util {

private static ObjectMapper objectMapper = new ObjectMapper();
private static Properties properties = null;

public static ObjectMapper getObjectMapper(){
return objectMapper;
}

public static Properties getProperties() throws IOException {
if ( properties != null){
return properties;
}
properties = new Properties();
InputStream inputStream = Util.class.getClassLoader().getResourceAsStream("application.properties");
properties.load(inputStream);
return properties;
}

public static String getHttpResponse(String urlStr) throws IOException {
URL url = new URL(urlStr);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setRequestProperty("Accept", "application/json");
conn.setConnectTimeout(5000);
//conn.setReadTimeout(20000);

if (conn.getResponseCode() != 200) {
throw new RuntimeException("Failed : HTTP error code : "
+ conn.getResponseCode());
}

BufferedReader br = new BufferedReader(new InputStreamReader(
(conn.getInputStream())));

StringBuilder outputBuilder = new StringBuilder();
String output;
while ((output = br.readLine()) != null) {
outputBuilder.append(output);
}
conn.disconnect();
return outputBuilder.toString();
}
}
[/java]

And So our Service class looks like:
[java]
//BookService.java
package info.sanaulla.service;

import com.fasterxml.jackson.databind.ObjectMapper;
import com.google.common.base.Optional;
import com.google.common.base.Strings;

import info.sanaulla.Constants;
import info.sanaulla.Util;
import info.sanaulla.model.Author;
import info.sanaulla.model.Book;

import java.io.IOException;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.Properties;

public class BookService {

public static Optional<Book> getBookDetailsFromGoogleBooks(String isbn13) throws IOException{
Properties properties = Util.getProperties();
String key = properties.getProperty(Constants.GOOGLE_API_KEY);
String url = "https://www.googleapis.com/books/v1/volumes?q=isbn:"+isbn13;
String response = Util.getHttpResponse(url);
Map bookMap = Util.getObjectMapper().readValue(response,Map.class);
Object bookDataListObj = bookMap.get("items");
Book book = null;
if ( bookDataListObj == null || !(bookDataListObj instanceof List)){
return Optional.fromNullable(book);
}

List bookDataList = (List)bookDataListObj;
if ( bookDataList.size() < 1){
return Optional.fromNullable(null);
}

Map bookData = (Map) bookDataList.get(0);
Map volumeInfo = (Map)bookData.get("volumeInfo");
book = new Book();
book.setTitle(getFromJsonResponse(volumeInfo,"title",""));
book.setPublisher(getFromJsonResponse(volumeInfo,"publisher",""));
List authorDataList = (List)volumeInfo.get("authors");
for(Object authorDataObj : authorDataList){
Author author = new Author();
author.setName(authorDataObj.toString());
book.addAuthor(author);
}
book.setIsbn13(isbn13);
book.setSummary(getFromJsonResponse(volumeInfo,"description",""));
book.setPageCount(Integer.parseInt(getFromJsonResponse(volumeInfo, "pageCount", "0")));
book.setPublishedDate(getFromJsonResponse(volumeInfo,"publishedDate",""));

return Optional.fromNullable(book);
}

private static String getFromJsonResponse(Map jsonData, String key, String defaultValue){
return Optional.fromNullable(jsonData.get(key)).or(defaultValue).toString();
}
}
[/java]

Adding caching on top of the Google Books API call

We can create a cache object using the CacheBuilder API provided by Guava library. It provides methods to set properties like

  • maximum items in cache,
  • time to live of the cache object based on its last write time or last access time,
  • ttl for refreshing the cache object,
  • recording stats on the cache like how many hits, misses, loading time and
  • providing a loader code to fetch the data in case of cache miss or cache refresh.

So what we would ideally want is that a cache miss should invoke our API written above i.e getBookDetailsFromGoogleBooks. And we would want to store maximum of 1000 items and expire the items after 24 hours. So the piece of code which builds the cache looks like:
[java collapse=”false”]
private static LoadingCache<String, Optional<Book>> cache = CacheBuilder.newBuilder()
.maximumSize(1000)
.expireAfterAccess(24, TimeUnit.HOURS)
.recordStats()
.build(new CacheLoader<String, Optional<Book>>() {
@Override
public Optional<Book> load(String s) throws IOException {
return getBookDetailsFromGoogleBooks(s);
}
});
[/java]

Its important to note that the maximum items which you want to store in the cache impact the heap used by your application. So you have to carefully decide this value depending on the size of each object you are going to cache and the maximum heap memory allocated to your application.

Lets put this into action and also see how the cache stats report the stats:

[java]
package info.sanaulla;

import com.google.common.cache.CacheStats;
import info.sanaulla.model.Book;
import info.sanaulla.service.BookService;

import java.io.IOException;
import java.util.Properties;
import java.util.concurrent.ExecutionException;

public class App
{
public static void main( String[] args ) throws IOException, ExecutionException {
Book book = BookService.getBookDetails("9780596009205").get();
System.out.println(Util.getObjectMapper().writeValueAsString(book));
book = BookService.getBookDetails("9780596009205").get();
book = BookService.getBookDetails("9780596009205").get();
book = BookService.getBookDetails("9780596009205").get();
book = BookService.getBookDetails("9780596009205").get();
CacheStats cacheStats = BookService.getCacheStats();
System.out.println(cacheStats.toString());
}
}
[/java]

And the output we would get is:
[shell]
{"isbn13":"9780596009205","authors":[{"name":"Kathy Sierra"},{"name":"Bert Bates"}],"publisher":""O’Reilly Media, Inc."","title":"Head First Java","summary":"An interactive guide to the fundamentals of the Java programming language utilizes icons, cartoons, and numerous other visual aids to introduce the features and functions of Java and to teach the principles of designing and writing Java programs.","pageCount":688,"publishedDate":"2005-02-09"}
CacheStats{hitCount=4, missCount=1, loadSuccessCount=1, loadExceptionCount=0, totalLoadTime=3744128770, evictionCount=0}
[/shell]

This is a very basic usage of Guava cache and I wrote it as I was learning to use this. In this I have made use of other Guava APIs like Optional which helps in wrapping around existent or non-existent(null) values into objects. This code is available on git hub- https://github.com/sanaulla123/Guava-Cache-Demo. There will be concerns such as how it handles concurrency which I havent gone detail into. But under the hood it uses a segmented Concurrent hash map such that the gets are always non-blocking, but the number of concurrent writes would be decided by the number of segments.

Some of the useful links related to this:
http://guava-libraries.googlecode.com/files/ConcurrentCachingAtGoogle.pdf

Very useful Console Window for windows

ConEmu (http://www.fosshub.com/ConEmu.html) is a very useful and much much better Console window for Windows. It acts as a facade over the cmd.exe. There are loads of good things in it and highly recommended for programmers who are windows users.

If you have installed Cygwin, you can integrate bash with your ComEmu terminal so that you can open a new tab running your bash shell:). On similar lines you can open new tabs running Git shell if you have installed git-shell.

To integrate Cygwin bash –
1. Open the setting – Windows + Alt + P
2. Select Startup -> Tasks
3. Click on “+” to add a new task
4. Name it as “Cygwin bash” or “cygwin” which ever is comfortable.
5. In the commands text area paste this: “%SystemDrive%cygwin64binbash.exe” –login -i
6. Save and exit the settings.

Book Review: Murach’s Java Servlets And JSP 3rd Edition

Murach’s Java Servlets and JSP is the ONLY book you need to learn Web App Development in Java using JSP and Servlets. The book covers all the concepts required you to build a complete Web application in Java. You will find topics covering:
– UI Development using HTML, Javascript
– Building Servlets for handling requests.
– Using JSP to create UI templates
– Building Data access layer to communicate with DB.

Its a completely hands on guide and just mere reading will be of no help. The book also covers concepts and techniques related to secure programming and also some advanced concepts in servlets.

Few among numerous salient features:
Completely hands on guide
Highly suitable for people who are familiar with Java language
Focuses on best practices where ever relevant. For example in the chapters which explains about JSP there is a guideline not to mix java code with JSP and instead make use of JSP Template Library.
Lot of reusable code snippets – useful if someone is looking to implement a subset of the feature explained.

I would highly recommend this book to –
“Any developer familiar with Java programming language looking to learn Web application development using Servlets and JSP”.

One can purchase the latest edition here [though currently only imported edition is available].

PS: I got a copy of the book in return for the review.

Book Review: RESTful Web Services with Dropwizard by Alexandros Dallas

RESTful Web Services with Dropwizard` by Alexandros Dallas is a good guide to get started with dropwizard. Dropwizard

The author covers most of the features of dropwizard which includes creating RESTful End points, Database access, Authentication, Creating views by means of developing a sample Phonebook application.

The book is not an exhaustive guide to dropwizard and may not match the documentation provided on the Dropwizard official site. But the approach of developing a sample application adding features in each chapter might appeal to some readers.

If you are kind of person who likes learning a framework by developing a sample application, then you can pick this book. Otherwise I would suggest the documentation would suffice.