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Processing large files efficiently in Java – multi-threaded code – part 2

If you want to process medium sized data (e.g. 2 GB to 100 GB in multiple files) in Java, consider writing a batch job with Spring batch or Java EE 7.0 batch processing. If processing requires access to other systems, use “spring integration” … Read more ›...

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Producer and Consumer Java Multi-threading code

The following code is used for demonstrating thread-safety issues on eclipse.

Step 1: ProducerConsumerTest

package com.debug.multithread;

public class ProducerConsumerTest {
    
    
    public static void main(String[] args) throws InterruptedException {
        
        ProducerConsumer pc = new ProducerConsumer();
        
        //spawn a new producer thread and start
        Thread producer = new Thread(new ProducerThread(pc));
        producer.start();
        
        Thread.sleep(10); //main thread sleeps for 1 second
        
        //spawn a new consumer thread and start
        Thread consumer = new Thread(new ConsumerThread(pc));
        consumer.start();
        
    }
}

package com.debug.multithread;

public class ProducerConsumerTest {

public static void main(String[] args) throws InterruptedException {

ProducerConsumer pc = new ProducerConsumer();

//spawn a new producer thread and start

Thread producer = new Thread(new ProducerThread(pc));

producer.start();

Thread.sleep(10); //main thread sleeps for 1 second

//spawn a new consumer thread and start

Thread consumer = new Thread(new ConsumerThread(pc));

consumer.start();

}

Step 2: Producer thread.

package com.debug.multithread;

public class ProducerThread implements Runnable {

    private ProducerConsumer pc;

    public ProducerThread(ProducerConsumer pc) {
        this.pc = pc;
    }

    @Override
    public void run() {
        pc.produce();
    }

}

package com.debug.multithread;

public class ProducerThread implements Runnable {

private ProducerConsumer pc;

public ProducerThread(ProducerConsumer pc) {

this.pc = pc;

}

@Override

public void run() {

pc.produce();

}

Step 3: Consumer thread.

package com.debug.multithread;

public class ConsumerThread implements Runnable {

    private ProducerConsumer pc;
        
    public ConsumerThread(ProducerConsumer pc) {
        this.pc = pc;
    }

    @Override
    public void run() {
        pc.consume();
    }

}

package com.debug.multithread;

public class ConsumerThread implements Runnable {

private ProducerConsumer pc;

public ConsumerThread(ProducerConsumer pc) {

this.pc = pc;

}

@Override

public void run() {

pc.consume();

}

Step 4: ProducerConsumer logic.

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Q1 – Q10 Java OOPs interview Q&As

If you don’t get Java OOPs interview questions & answers right in the job interviews you can say OOPS !!!! to your Java interview success. Q1. Is Java a 100% Object Oriented (OO) language? if yes why? and if no, why not? A1. … Read more ›...

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Q6 – Q11 Swing interview questions and answers

Extends Q1 to Q5 Swing interview questions and answers.

Q6. If you add a component to the CENTER of a border layout, which directions will the component stretch?
A6. The component will stretch both horizontally and vertically. It will occupy the whole space in the middle.

…

Read a text file from Java classpath

File to read: src/main/resources/examples/request.xml

<employee>
    <name>Peter Smith</name>
    <age>25</age>
</employee>

<name>Peter Smith</name>

</employee>

1. Using Java API without any libraries

package com.mytutorial;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;


public class ReadTextFileFromClasspath {

    public static void main(String[] args) throws IOException {
        InputStream is = ReadTextFileFromClasspath.class.getResourceAsStream("/examples/request.xml");
        InputStreamReader isr = new InputStreamReader(is);
        StringBuilder sb=new StringBuilder();
        BufferedReader br = new BufferedReader(isr);
        String read = br.readLine();

        while(read != null) {
            sb.append(read);
            read =br.readLine();
            sb.append("\n");
        }

        System.out.println(sb.toString());
    }
}

package com.mytutorial;

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

public class ReadTextFileFromClasspath {

public static void main(String[] args) throws IOException {

InputStream is = ReadTextFileFromClasspath.class.getResourceAsStream("/examples/request.xml");

InputStreamReader isr = new InputStreamReader(is);

StringBuilder sb=new StringBuilder();

BufferedReader br = new BufferedReader(isr);

String read = br.readLine();

while(read != null) {

sb.append(read);

read =br.readLine();

sb.append("\n");

}

System.out.println(sb.toString());

}

You can also use the “ClassLoader”

ClassLoader loader = Thread.currentThread().getContextClassLoader();
InputStream is = loader.getResourceAsStream("examples/request.xml");

1 2	ClassLoader loader = Thread.currentThread().getContextClassLoader(); InputStream is = loader.getResourceAsStream("examples/request.xml");

2. Using Java 7 NIO

 package com.mytutorial;

import java.io.IOException;
import java.net.URISyntaxException;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;


public class ReadTextFileFromClasspath {

    public static void main(String[] args) throws IOException, URISyntaxException {

        List<String> readLines = Files.readAllLines(
            Paths.get(ReadTextFileFromClasspath.class.getResource("/examples/request.xml").toURI()), Charset.defaultCharset());

        System.out.println(readLines);
    }
}

package com.mytutorial;

import java.io.IOException;

import java.net.URISyntaxException;

import java.nio.charset.Charset;

import java.nio.file.Files;

import java.nio.file.Paths;

import java.util.List;

public class ReadTextFileFromClasspath {

public static void main(String[] args) throws IOException, URISyntaxException {

List<String> readLines = Files.readAllLines(

Paths.get(ReadTextFileFromClasspath.class.getResource("/examples/request.xml").toURI()), Charset.defaultCharset());

System.out.println(readLines);

}

…

Reading a text file in Java with the Scanner

As a Java developer it is a very common task to read file contents to a String object. It is also very common in pre-interview written tests read the contents of a file and apply regex to split string, etc.

4 things to watch-out for in File processing

1) Files must be closed once read.

…

Reloading configuration files in Java without stopping the server

Q1. Why & when do you want to use properties files for the project configuration as opposed to Java constants?
A1. It is a best practice to externalize application related properties that are likely to change. If you hard code the properties that are likely to change,

…

Searching algorithms in Java

This assumes that you understand “Swapping, partitioning, and sorting algorithms in Java“. Q1. Can you write a code to search for number 5 in 7 3 6 8 2 9 5 4? A1. The code below uses the linear search algorithm. … Read more ›...

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Sorting a Map by values instead of keys

This post is motivated by ““Sorting a list or array of numbers by frequency of occurrences in Java”

Sorting a Map by Keys

Sorting a map by its keys is straightforward


SortedSet<String> keys = new TreeSet<String>(map.keySet());

SortedSet<String> keys = new TreeSet<String>(map.keySet());

Sorting a Map by its Values –

…

Splitting input text & string processing coding Q&A

Q1. Can you write code to extract numbers from a given input text and return the sum of those numbers? Example: “1 some text 2 more text 4 more text 8” should return 15 as the sum. A The key steps are: 1. … Read more ›...

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Swapping, partitioning, and sorting algorithms in Java

Q1. Can you write an algorithm in Java to swap two variables? A1.

public class Swap {
    
    public static void main(String[ ] args) {
        int x = 5;
        int y = 6;
        
        //store 'x' in a temp variable
        int temp = x;
        x = y;
        y = temp;
        
        System.out.println("x=" + x + ",y=" + y);
   }
}

public class Swap {

public static void main(String[ ] args) {

int x = 5;

int y = 6;

//store 'x' in a temp variable

int temp = x;

x = y;

y = temp;

System.out.println("x=" + x + ",y=" + y);

}

Q2. Can you write an algorithm to bubble sort the following array { 30, 12, 18, 0, -5, 72, 424 }?? … Read more ›...

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Top 5 Core Java Exceptions and best practices

#1: ConcurrentModificationException Getting a ConcurrentModificationException when trying to modify (i.e. adding or removing an item) a collection while iterating. The following code throws a ConcurrentModificationException.

List<T> list = getListOfItems();
for (Iterator<T> iter = list.iterator(); iter.hasNext(); ) {
  T obj = iter.next();
  if (obj.someCondition()) {
    list.remove(0); // ConcurrentModificationException
  }
}

List<T> list = getListOfItems();

for (Iterator<T> iter = list.iterator(); iter.hasNext(); ) {

T obj = iter.next();

if (obj.someCondition()) {

list.remove(0); // ConcurrentModificationException

}

To avoid ConcurrentModificationException in a single-threaded environment, you can remove the object that you are working on with the iterator. … Read more ›...

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Top 6 Java 8 features you can start using now

Unlike Java 7, Java 8 has some significant changes. You can get familiarised with the the following simple working code. All you need is Java 8 installed on your machine.

#1: Interface can have static and default methods. This tries to solve the diamond (aka multiple inheriance) issue.

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Blog Archives

Processing large files efficiently in Java – multi-threaded code – part 2

Producer and Consumer Java Multi-threading code

Q1 – Q10 Java OOPs interview Q&As

Q6 – Q11 Swing interview questions and answers

Read a text file from Java classpath

Reading a text file in Java with the Scanner

Reloading configuration files in Java without stopping the server

Searching algorithms in Java

Sorting a Map by values instead of keys

Splitting input text & string processing coding Q&A

Swapping, partitioning, and sorting algorithms in Java

Top 5 Core Java Exceptions and best practices

Top 6 Java 8 features you can start using now

300+ Java Interview Questions - FAQs

10+ Companion Techs Interview Q&As

300+ Big Data Interview Questions - FAQs

16+ Java Tech Key Areas Interview Q&As

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