Category Archives: Code

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

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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:

//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;
  }
}

And the Author class is defined as:

//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;
  }

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:

//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();
  }
}

And So our Service class looks like:

//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();
  }
}

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:

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);
      }
  });

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:

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());
  }
}
[/cpde]

And the output we would get is:

{"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}

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.

Simple Aspect Oriented Programming (AOP) using CDI in JavaEE

We write service APIs which cater to certain business logic. There are few cross-cutting concerns that cover all service APIs like Security, Logging, Auditing, Measuring Latencies and so on. This is a repetitive non-business code which can be reused among other methods. One way to reuse is to move these repetitive code into its own methods and invoke them in the service APIs somethings like:

public class MyService{
   public ServiceModel service1(){
      isAuthorized();
      //execute business logic.
   }
}

public class MyAnotherService{
  public ServiceModel service1(){
    isAuthorized():
    //execute business logic. 
  }
}

The above approach will work but not without creating code noise, mixing cross-cutting concerns with the business logic. There is another approach to solve the above requirements which is by using Aspect and this approach is called Aspect Oriented Programming (AOP). There are a different ways you can make use of AOP – by using Spring AOP, JavaEE AOP. In this example I Will try to use AOP using CDI in Java EE applications. To explain this I have picked a very simple example of building a web application to fetch few records from Database and display in the browser.

Creating the Data access layer

The table structure is:

create table people(
    id INT NOT NULL AUTO_INCREMENT, 
    name varchar(100) NOT NULL,
    place varchar(100),
    primary key(id));

Lets create a Model class to hold a person information

package demo.model;
public class Person{
  private String id;
  private String name;
  private String place;
  public String getId(){ return id; } 
  public String setId(String id) { this.id = id;}
  public String getName(){ return name; } 
  public String setName(String name) { this.name = name;}
  public String getPlace(){ return place; } 
  public String setPlace(String place) { this.place = place;}
}

Lets create a Data Access Object which exposes two methods –

  1. to fetch the details of all the people
  2. to fetch the details of one person of given id
package demo.dao;

import demo.common.DatabaseConnectionManager;
import demo.model.Person;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

public class PeopleDAO {

    public List<Person> getAllPeople() throws SQLException {
        String SQL = "SELECT * FROM people";
        Connection conn = DatabaseConnectionManager.getConnection();
        List<Person> people = new ArrayList<>();
        try (Statement statement = conn.createStatement();
                ResultSet rs = statement.executeQuery(SQL)) {
            while (rs.next()) {
                Person person = new Person();
                person.setId(rs.getString("id"));
                person.setName(rs.getString("name"));
                person.setPlace(rs.getString("place"));
                people.add(person);
            }
        }
        return people;
    }

    public Person getPerson(String id) throws SQLException {
        String SQL = "SELECT * FROM people WHERE id = ?";
        Connection conn = DatabaseConnectionManager.getConnection();
        try (PreparedStatement ps = conn.prepareStatement(SQL)) {
            ps.setString(1, id);
            try (ResultSet rs = ps.executeQuery()) {
                if (rs.next()) {
                    Person person = new Person();
                    person.setId(rs.getString("id"));
                    person.setName(rs.getString("name"));
                    person.setPlace(rs.getString("place"));
                    return person;
                }
            }
        }

        return null;
    }
}

You can use your own approach to get a new Connection. In the above code I have created a static utility that returns me the same connection.

Creating Interceptors

Creating Interceptors involves 2 steps:

  1. Create Interceptor binding which creates an annotation annotated with @InterceptorBinding that is used to bind the interceptor code and the target code which needs to be intercepted.
  2. Create a class annotated with @Interceptor which contains the interceptor code. It would contain methods annotated with @AroundInvoke, different lifecycle annotations, @AroundTimeout and others.

Lets create an Interceptor binding by name @LatencyLogger

package demo;

import java.lang.annotation.Target;
import java.lang.annotation.Retention;
import static java.lang.annotation.RetentionPolicy.*;
import static java.lang.annotation.ElementType.*;
import javax.interceptor.InterceptorBinding;

@InterceptorBinding
@Retention(RUNTIME)
@Target({METHOD, TYPE})
public @interface LatencyLogger {
    
}

Now we need to create the Interceptor code which is annotated with @Interceptor and also annotated with the Interceptor binding we created above i.e @LatencyLogger:

package demo;
import java.io.Serializable;
import javax.interceptor.AroundInvoke;
import javax.interceptor.Interceptor;
import javax.interceptor.InvocationContext;

@Interceptor
@LatencyLogger
public class LatencyLoggerInterceptor implements Serializable{
  
  @AroundInvoke
    public Object computeLatency(InvocationContext invocationCtx) throws Exception{
        long startTime = System.currentTimeMillis();
        //execute the intercepted method and store the return value
        Object returnValue = invocationCtx.proceed();
        long endTime = System.currentTimeMillis();
        System.out.println("Latency of " + invocationCtx.getMethod().getName() +": " + (endTime-startTime)+"ms");
        return returnValue;
        
    }
}

There are two interesting things in the above code:

  1. use of @AroundInvoke
  2. parameter of type InvocationContext passed to the method

@AroundInvoke designates the method as an interceptor method. An Interceptor class can have only ONE method annotated with this annotation. When ever a target method is intercepted, its context is passed to the interceptor. Using the InvocationContext one can get the method details, the parameters passed to the method.

We need to declare the above Interceptor in the WEB-INF/beans.xml file

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://xmlns.jcp.org/xml/ns/javaee"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/beans_1_1.xsd"
       bean-discovery-mode="all">
    
    <interceptors>
        <class>demo.LatencyLoggerInterceptor</class>
    </interceptors>
</beans>

Creating Service APIs annotated with Interceptors

We have already created the Interceptor binding and the interceptor which gets executed. Now lets create the Service APIs and then annotate them with the Interceptor binding

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package demo.service;

import demo.LatencyLogger;
import demo.dao.PeopleDAO;
import demo.model.Person;
import java.sql.SQLException;
import java.util.List;
import javax.inject.Inject;

public class PeopleService {

  @Inject
  PeopleDAO peopleDAO;

  @LatencyLogger
  public List<Person> getAllPeople() throws SQLException {
    return peopleDAO.getAllPeople();
  }

  @LatencyLogger
  public Person getPerson(String id) throws SQLException {
    return peopleDAO.getPerson(id);
  }

}

We have annotated the service methods with the Interceptor binding @LatencyLogger. The other way would be to annotate at the class level which would then apply the annotation to all the methods of the class. Another thing to notice is the @Inject annotation that injects the instance i.e injects the dependency into the class.

Next is to wire up the Controller and View to show the data. The controller is the servlet and view is a plain JSP using JSTL tags.

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package demo;

import demo.model.Person;
import demo.service.PeopleService;
import java.io.IOException;
import java.sql.SQLException;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.inject.Inject;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet(name = "AOPDemo", urlPatterns = {"/AOPDemo"})
public class AOPDemoServlet extends HttpServlet {

  @Inject
  PeopleService peopleService;

  @Override
  public void doGet(HttpServletRequest request, HttpServletResponse response)
          throws ServletException, IOException {
    try {
      List<Person> people = peopleService.getAllPeople();
      Person person = peopleService.getPerson("2");
      request.setAttribute("people", people);
      request.setAttribute("person", person);
      getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
    } catch (SQLException ex) {
      Logger.getLogger(AOPDemoServlet.class.getName()).log(Level.SEVERE, null, ex);
    }
  }
}

The above servlet is available at http://localhost:8080//AOPDemo. It fetches the data and redirects to the view to display the same. Note that the Service has also been injected using @Inject annotation. If the dependencies are not injected and instead created using new then the Interceptors will not work. This is an important point which I realised while building this sample.

The JSP to render the data would be

<%@page contentType="text/html" pageEncoding="UTF-8"%>
<%@ taglib prefix="c" 
           uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE html>
<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>AOP Demo</title>
  </head>
  <body>
    <h1>Hello World!</h1>
    <table>
      <tr>
        <th>Id</th>
        <th>Name</th>
        <th>Place</th>
      </tr>
      <c:forEach items="${requestScope.people}" var="person">
        <tr>
          <td><c:out value="${person.id}"/></td>
          <td><c:out value="${person.name}"/></td>
          <td><c:out value="${person.place}"/></td>
        </tr>
      </c:forEach>
    </table>
    <br/>
    Details for person with id=2
    <c:out value="Name ${person.name} from ${person.place}" />
  </body>
</html>

With this you would have built a very simple app using Interceptors. Thanks for reading and staying with me till this end. Please share your queries/feedback as comments. And also share this article among your friends 🙂

Getting started with Mocking in Java using Mockito

We all write unit tests but the challenge we face at times is that the unit under test might be dependent on other components. And configuring other components for unit testing is definitely an overkill. Instead we can make use of Mocks in place of the other components and continue with the unit testing.

To show how one can use mocks, I have a Data access layer(DAL), basically a class which provides an API for the application to access and modify the data in the data repository. I then unit test the DAL without actually the need to connect to the data repository. The data repository can be a local database or remote database or a file system or any place where we can store and retrieve the data. The use of a DAL class helps us in keeping the data mappers separate from the application code.

Lets create a Java project using maven.

mvn archetype:generate -DgroupId=info.sanaulla -DartifactId=MockitoDemo -DarchetypeArtifactId=maven-archetype-quickstart -DinteractiveMode=false

The above creates a folder MockitoDemo and then creates the entire directory structure for source and test files.

Consider the below model class for this example:

package info.sanaulla.models;

import java.util.List;

/**
* Model class for the book details.
*/
public class Book {

  private String isbn;
  private String title;
  private List<String> authors;
  private String publication;
  private Integer yearOfPublication;
  private Integer numberOfPages;
  private String image;

  public Book(String isbn,
              String title,
              List<String> authors,
              String publication,
              Integer yearOfPublication,
              Integer numberOfPages,
              String image){

    this.isbn = isbn;
    this.title = title;
    this.authors = authors;
    this.publication = publication;
    this.yearOfPublication = yearOfPublication;
    this.numberOfPages = numberOfPages;
    this.image = image;

  }

  public String getIsbn() {
    return isbn;
  }

  public String getTitle() {
    return title;
  }

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

  public String getPublication() {
    return publication;
  }

  public Integer getYearOfPublication() {
    return yearOfPublication;
  }

  public Integer getNumberOfPages() {
    return numberOfPages;
  }

  public String getImage() {
    return image;
  }
}

The DAL class for operating on the Book model class is:

package info.sanaulla.dal;

import info.sanaulla.models.Book;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

/**
* API layer for persisting and retrieving the Book objects.
*/
public class BookDAL {

  private static BookDAL bookDAL = new BookDAL();

  public List<Book> getAllBooks(){
      return Collections.EMPTY_LIST;
  }

  public Book getBook(String isbn){
      return null;
  }

  public String addBook(Book book){
      return book.getIsbn();
  }

  public String updateBook(Book book){
      return book.getIsbn();
  }

  public static BookDAL getInstance(){
      return bookDAL;
  }
}

The DAL layer above currently has no functionality and we are going to unit test that piece of code (TDD). The DAL layer might communicate with a ORM Mapper or Database API which we are not concerned while designing the API.

Test driving the DAL layer

There are lot of frameworks for Unit testing and mocking in Java but for this example I would be picking JUnit for unit testing and Mockito for mocking. We would have to update the dependency in Maven’s 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>info.sanaulla</groupId>
  <artifactId>MockitoDemo</artifactId>
  <packaging>jar</packaging>
  <version>1.0-SNAPSHOT</version>
  <name>MockitoDemo</name>
  <url>http://maven.apache.org</url>
  <dependencies>
    <!-- Dependency for JUnit -->
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.10</version>
      <scope>test</scope>
    </dependency>
    <!-- Dependency for Mockito -->
    <dependency>
      <groupId>org.mockito</groupId>
      <artifactId>mockito-all</artifactId>
      <version>1.9.5</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
</project>

Now lets unit test the BookDAL. During the unit testing we will inject mock data into the BookDAL so that we can complete the testing of the API without depending on the data source.

Initially we will have an empty test class:

public class BookDALTest {
  public void setUp() throws Exception {

  }

  public void testGetAllBooks() throws Exception {

  }

  public void testGetBook() throws Exception {

  }

  public void testAddBook() throws Exception {

  }

  public void testUpdateBook() throws Exception {

  }
}

We will inject the mock BookDAL and mock data in the setUp() as shown below:

public class BookDALTest {

  private static BookDAL mockedBookDAL;
  private static Book book1;
  private static Book book2;

  @BeforeClass
  public static void setUp(){
    //Create mock object of BookDAL
    mockedBookDAL = mock(BookDAL.class);

    //Create few instances of Book class.
    book1 = new Book("8131721019","Compilers Principles",
            Arrays.asList("D. Jeffrey Ulman","Ravi Sethi", "Alfred V. Aho", "Monica S. Lam"),
            "Pearson Education Singapore Pte Ltd", 2008,1009,"BOOK_IMAGE");

    book2 = new Book("9788183331630","Let Us C 13th Edition",
            Arrays.asList("Yashavant Kanetkar"),"BPB PUBLICATIONS", 2012,675,"BOOK_IMAGE");

    //Stubbing the methods of mocked BookDAL with mocked data. 
    when(mockedBookDAL.getAllBooks()).thenReturn(Arrays.asList(book1, book2));
    when(mockedBookDAL.getBook("8131721019")).thenReturn(book1);
    when(mockedBookDAL.addBook(book1)).thenReturn(book1.getIsbn());
    when(mockedBookDAL.updateBook(book1)).thenReturn(book1.getIsbn());
  }

  public void testGetAllBooks() throws Exception {}

  public void testGetBook() throws Exception {}

  public void testAddBook() throws Exception {}

  public void testUpdateBook() throws Exception {}
}

In the above setUp() method I have:

  1. Created a mock object of BookDAL
    BookDAL mockedBookDAL = mock(BookDAL.class);
    
  2. Stubbed the API of BookDAL with mock data, such that when ever the API is invoked the mocked data is returned.
    //When getAllBooks() is invoked then return the given data and so on for the other methods.
    when(mockedBookDAL.getAllBooks()).thenReturn(Arrays.asList(book1, book2));
    when(mockedBookDAL.getBook("8131721019")).thenReturn(book1);
    when(mockedBookDAL.addBook(book1)).thenReturn(book1.getIsbn());
    when(mockedBookDAL.updateBook(book1)).thenReturn(book1.getIsbn());
    

Populating the rest of the tests we get:

package info.sanaulla.dal;

import info.sanaulla.models.Book;
import org.junit.BeforeClass;
import org.junit.Test;

import static org.junit.Assert.*;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.when;

import java.util.Arrays;
import java.util.List;


public class BookDALTest {

  private static BookDAL mockedBookDAL;
  private static Book book1;
  private static Book book2;

  @BeforeClass
  public static void setUp(){
    mockedBookDAL = mock(BookDAL.class);
    book1 = new Book("8131721019","Compilers Principles",
            Arrays.asList("D. Jeffrey Ulman","Ravi Sethi", "Alfred V. Aho", "Monica S. Lam"),
            "Pearson Education Singapore Pte Ltd", 2008,1009,"BOOK_IMAGE");

    book2 = new Book("9788183331630","Let Us C 13th Edition",
            Arrays.asList("Yashavant Kanetkar"),"BPB PUBLICATIONS", 2012,675,"BOOK_IMAGE");

    when(mockedBookDAL.getAllBooks()).thenReturn(Arrays.asList(book1, book2));
    when(mockedBookDAL.getBook("8131721019")).thenReturn(book1);
    when(mockedBookDAL.addBook(book1)).thenReturn(book1.getIsbn());

    when(mockedBookDAL.updateBook(book1)).thenReturn(book1.getIsbn());

  }

  @Test
  public void testGetAllBooks() throws Exception {

    List<Book> allBooks = mockedBookDAL.getAllBooks();
    assertEquals(2, allBooks.size());
    Book myBook = allBooks.get(0);
    assertEquals("8131721019", myBook.getIsbn());
    assertEquals("Compilers Principles", myBook.getTitle());
    assertEquals(4, myBook.getAuthors().size());
    assertEquals((Integer)2008, myBook.getYearOfPublication());
    assertEquals((Integer) 1009, myBook.getNumberOfPages());
    assertEquals("Pearson Education Singapore Pte Ltd", myBook.getPublication());
    assertEquals("BOOK_IMAGE", myBook.getImage());
  }

  @Test
  public void testGetBook(){

    String isbn = "8131721019";

    Book myBook = mockedBookDAL.getBook(isbn);

    assertNotNull(myBook);
    assertEquals(isbn, myBook.getIsbn());
    assertEquals("Compilers Principles", myBook.getTitle());
    assertEquals(4, myBook.getAuthors().size());
    assertEquals("Pearson Education Singapore Pte Ltd", myBook.getPublication());
    assertEquals((Integer)2008, myBook.getYearOfPublication());
    assertEquals((Integer)1009, myBook.getNumberOfPages());

  }

  @Test
  public void testAddBook(){
    String isbn = mockedBookDAL.addBook(book1);
    assertNotNull(isbn);
    assertEquals(book1.getIsbn(), isbn);
  }

  @Test
  public void testUpdateBook(){

    String isbn = mockedBookDAL.updateBook(book1);
    assertNotNull(isbn);
    assertEquals(book1.getIsbn(), isbn);
  }
}

One can run the test by using maven command: mvn test. The output is:

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running info.sanaulla.AppTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.029 sec
Running info.sanaulla.dal.BookDALTest
Tests run: 4, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.209 sec

Results :

Tests run: 5, Failures: 0, Errors: 0, Skipped: 0

So we have been able to test the DAL class without actually configuring the data source by using mocks.

JSON Processing support in JavaEE 7 and JSR-353

JSON processing is not supported out of the box in Java. One would have to make use of 3rd part libraries to enable JSON processing. But with JSR 353 and its reference implementation JSON processing is being brought into the Java language. JavaEE 7 has already included the reference implementation.

I wrote a series of articles explaining how to parse and create JSON data using the JSR 353 implementation: