Amount credited in account Rs. 500

 Now suppose attacker provide the input \n\n Amount debited in account Rs.500

Amount credited in account Rs. 500

Amount debited in account Rs.500

So, attacker forged the logs by making a fake or forge entry in log.

Avoid directly embedding user input in log files when possible. Sanitize untrusted data used to construct log entries by using safe logging mechanism such as OWASP ESAPI logger, which will automatically remove unexpected carriage returns. So, to prevent this, we use use ESAPI Logger mechanism.

Here is the dependency of ESAPI: 

<dependency>

<groupId>org.owasp.esapi</groupId>

<artifactId>esapi</artifactId>

<version>2.2.2.0</version>

</dependency>

We can encode the logs using ESAPI‘s Encoder method and interface:

    public String encode(String message) {
    message = message.replace( '\n' ,  '_' ).replace( '\r' , '_' )
      .replace( '\t' , '_' );
    message = ESAPI.encoder().encodeForHTML( message );
    return message;
}

How we can create a new project in Angular?

To create a new project, open Angular CLI and type below mentioned command and press enter. This will take some time to create an ready to build application for you.

ng new angular-project

Now this will create a full ready to build angular application. In below image you can see the full folder structure of angular application.

Run or Serve application

cd angular-project

ng serve

How to install Angular?

Which IDE is used for angular?

Install Node.js

Angular CLI

SPA (Single Page Application)

Angular Tutorial: Getting Started With Angular 

Welcome to Angular tutorials, in this tutorial i will cover all the topics of angular and after this tutorial you will be able to write the code of angular.

So lets start the tutorial step by step.

1. What is Angular
2. Installation
3. Getting Started with Angular 
4. Angular Features
5. Differences between AngularJS and Angular
6. Angular Directives
7. Angular Pipes
8. Angular Databinding
9. Angular CLI
10. Forms
• Form Validation
• HTTP
• Router
• Module
• Styling
• Errors
• Configuration

package com.string.codebyakram;

import java.util.HashMap;

public class NonReapingCahr {
 public static void main(String[] args) {
  String string = "hello";
  System.out.println(findNonReapingCahr(string));
 }

 public static char findNonReapingCahr(String string) {

  HashMap< character > countChar = new HashMap<>();

  for (int i = 0; i < string.length(); i++) {
   int count = countChar.get(string.charAt(i)) == null ? 1 : countChar.get(string.charAt(i)) + 1;
   countChar.put(string.charAt(i), count);
  }

  for (int i = 0; i < string.length(); i++) {
   if (countChar.get(string.charAt(i)) == 1) {
    return string.charAt(i);
   }
  }
  return '\0';

 }
}

log4j.rootLogger=TRACE, stdout
log4j.appender.dataLogs=org.apache.log4j.FileAppender
log4j.appender.dataLogs.File=logs/logFile1.log
log4j.appender.dataLogs.layout=org.apache.log4j.PatternLayout
log4j.appender.dataLogs.layout.ConversionPattern=%d [%24F:%t:%L] - %m%n
log4j.appender.reportsLog=org.apache.log4j.FileAppender
log4j.appender.reportsLog.File=logs/logFile2.log
log4j.appender.reportsLog.layout=org.apache.log4j.PatternLayout
log4j.appender.reportsLog.layout.ConversionPattern=%d [%24F:%t:%L] - %m%n

log4j.category.dataLogger=TRACE, dataLogs
log4j.additivity.debugLogger=false
log4j.category.reportsLogger=DEBUG, reportsLog
log4j.additivity.reportsLogger=false

static final Logger debugLog = Logger.getLogger("dataLogger");
static final Logger resultLog = Logger.getLogger("reportsLogger");

package com.avaya.deletelogs;

import java.io.File;
import java.io.FilenameFilter;
import java.util.Arrays;
import java.util.List;

public class DeleteLogs {

 private String baseDir = "/opt/java/IVRLog";
 private int daysBack = 4;

 public void invokeProcess() {
  getFolders();
 }

 public void getFolders() {

  try {
   File file = new File(baseDir);
   String[] directories = file.list(new FilenameFilter() {

    public boolean accept(File current, String name) {
     return new File(current, name).isDirectory();
    }
   });
   deleteFiles(daysBack, baseDir, Arrays.asList(directories));
  } catch (Exception e) {
   System.out.println(e);
  }
 }

 public void deleteFiles(int daysBack, String dirWay, List< string> directories) {
  for (String dir : directories) {
   deleteFilesOlderThanNdays(daysBack, dir);
  }

 }

 public void deleteFilesOlderThanNdays(int daysBack, String dirWay) {

  File directory = new File(baseDir + "/" + dirWay);
  if (directory.exists()) {

   File[] listFiles = directory.listFiles();
   long purgeTime = System.currentTimeMillis() - (daysBack * 24 * 60 * 60 * 1000);
   for (File listFile : listFiles) {
    try {
     if (listFile.isFile()) {
      if (listFile.lastModified() < purgeTime) {
       if (!listFile.delete()) {
        System.err.println("Unable to delete file: " + listFile);
       }
      }
     } else {
      continue;
     }
    } catch (Exception e) {
     System.out.println(e);
    }
   }
  }
 }

}

Partial Dependency

Overriding

Changes

Number of dependencies

Lets se how we can sort the object by using java 8 lambda comparator. For this let take a Employee class.

public class Employee {
    private String name;
    private int salary;
 
    // standard constructors, getters/setters, equals and hashcode
}

1. Classic sort (without lambda)

Comparator< Employee > bySalary = new Comparator< Employee >() {
  @Override
  public int compare(Employee o1, Employee o2) {
   return o1.getSalary().compareTo(o2.getSalary());
  }
 };

2. Lambda expression equivalent.

 Comparator< Employee > bySalary = 
  (Employee o1, Employee o2)->o1.getSalary().compareTo(o2.getSalary());

You may also like to read What do you mean by Aspect, Join Point, Advice?

As we know, map is based on key-value pair associations, so interviewer can ask you this question if you are a beginner or having less than 3 years of experience.

So lets see how we can the key and values from a Map?

In Java we have and Map.Entry method that returns a collection-view of map.

Map< string string=""> map = new HashMap<>();

 // Get keys and values
 for (Map.Entry< string string=""> entry : map.entrySet()) {
  String k = entry.getKey();
  String v = entry.getValue();
  System.out.println("Key: " + k + ", Value: " + v);
 }

 // In Java 8 we can use for each
 map.forEach((k, v) -> {
  System.out.println("Key: " + k + ", Value: " + v);
 });

We can set the timeout for RestTemplate by doing some custom configuration for RestTemplate.

First you need to create a class named as HttpClientConfig in this class we configure HttpClient because RestTemplate internally uses the HttpClient.

package com.codebyakram;

import org.apache.http.client.config.RequestConfig;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.slf4j.Logger;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class HttpClientConfig {

 public static final Logger LOGGER = org.slf4j.LoggerFactory.getLogger(HttpClientConfig.class.getName());
 // Determines the timeout in milliseconds until a connection is established.
 private static final int CONNECT_TIMEOUT = 30000;

 // The timeout when requesting a connection from the connection manager.
 
 private int REQUEST_TIMEOUT = 10000;
 
 @Bean
 public CloseableHttpClient httpClient() {
  RequestConfig requestConfig = RequestConfig.custom().setConnectionRequestTimeout(REQUEST_TIMEOUT).build();
  return HttpClients.custom().setDefaultRequestConfig(requestConfig).build();
 }
}

Here in this class we setting HttpClient in RestTemplate

package com.codebyakram;

import org.apache.http.impl.client.CloseableHttpClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
import org.springframework.scheduling.TaskScheduler;
import org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler;
import org.springframework.web.client.RestTemplate;

@Configuration
public class RestTemplateConfig {

 @Autowired
 CloseableHttpClient httpClient;


 @Bean
 public RestTemplate restTemplate() {
  RestTemplate restTemplate = new RestTemplate(clientHttpRequestFactory());
  return restTemplate;
 }

 @Bean
 public HttpComponentsClientHttpRequestFactory clientHttpRequestFactory() {
  HttpComponentsClientHttpRequestFactory clientHttpRequestFactory = new HttpComponentsClientHttpRequestFactory();
  clientHttpRequestFactory.setHttpClient(httpClient);
  return clientHttpRequestFactory;
 }

 @Bean
 public TaskScheduler taskScheduler() {
  ThreadPoolTaskScheduler scheduler = new ThreadPoolTaskScheduler();
  scheduler.setThreadNamePrefix("poolScheduler");
  scheduler.setPoolSize(50);
  return scheduler;
 }
}

Interviewer may ask you this question if you have more than 3 years of experience in java development. So lets have a look, how to sort a stack using merge sort?

Lets see sample input and output for better understanding:

Algorithm
For this we will follow these below two steps,
1. Break the stack into two parts by using two temporary stack.

2. When only one element remains on a Stack, Merge it.

Lets have a look on the program,

package com.codebyakram;
 
import java.util.Stack;
 
public class SortStack {
 
    public static void main(String args[]) {
        Stack stack = new Stack();
        stack.push(5);
        stack.push(9);
        stack.push(4);
        stack.push(1);
        stack.push(2);
        stack.push(-1);

 
        sort(stack);
 
        System.out.println(stack);
    }
 
    private static void sort(Stack stack) {
        Stack s1 = new Stack();
        Stack s2 = new Stack();
 
        while (stack.size() != 0) {
            if (stack.size() % 2 == 0) {
                s1.push(stack.pop());
            } else {
                s2.push(stack.pop());
            }
        }
 
        if (s1.size() > 1) {
            sort(s1);
        }
 
        if (s2.size() > 1) {
            sort(s2);
        }
 
        merge(s1, s2, stack);
    }
 
    private static void merge(Stack s1, Stack s2, Stack stack) {
        Stack mergedStack = new Stack();
        while (!s1.isEmpty() && !s2.isEmpty()) {
            if ((Integer) s1.peek() < (Integer) s2.peek()) {
                mergedStack.push(s2.pop());
            } else {
                mergedStack.push(s1.pop());
            }
        }
 
        while (!s1.isEmpty()) {
            mergedStack.push(s1.pop());
        }
 
        while (!s2.isEmpty()) {
            mergedStack.push(s2.pop());
        }
 
        while (!mergedStack.isEmpty()) {
            stack.push(mergedStack.pop());
        }
    }
}

An adjacency list represents a graph as an array of linked list.

The index of the array represents a vertex and each element in its linked list represents the other vertices that form an edge with the vertex.

Adjacency List representation
A graph and its equivalent adjacency list representation is shown below.

An adjacency list is efficient in terms of storage because we only need to store the values for the edges. For a sparse graph with millions of vertices and edges, this can mean a lot of saved space.

Adjacency List Structure
The simplest adjacency list needs a node data structure to store a vertex and a graph data structure to organize the nodes.


We stay close to the basic definition of graph - a collection of vertices and edges {V, E}. For simplicity we use an unlabeled graph as opposed to a labeled one i.e. the vertexes are identified by their indices 0,1,2,3.

Let's dig into the data structures.

struct node
{
    int vertex;
    struct node* next;
};
struct Graph
{
    int numVertices;
    struct node** adjLists;
};

Don't let the struct node** adjLists overwhelm you.

All we are saying is we want to store a pointer to struct node*. This is because we don't know how many vertices the graph will have and so we cannot create an array of Linked Lists at compile time.

Adjacency List Java
We use Java Collections to store the Array of Linked Lists.

class Graph
{
    private int numVertices;
    private LinkedList adjLists[];
}

The type of LinkedList is determined what data you want to store in it. For a labeled graph, you could store a dictionary instead of an Integer

Adjacency List code Java

import java.io.*;
import java.util.*;
class Graph
{
    private int numVertices;
    private LinkedList adjLists[];
 
    Graph(int vertices)
    {
        numVertices = vertices;
        adjLists = new LinkedList[vertices];
        
        for (int i = 0; i < vertices; i++)
            adjLists[i] = new LinkedList();
    }
 
    void addEdge(int src, int dest)
    {
        adjLists[src].add(dest);
    }
 
    public static void main(String args[])
    {
        Graph g = new Graph(4);
 
         g.addEdge(0, 1);
         g.addEdge(0, 2);
         g.addEdge(1, 2);
         g.addEdge(2, 3);
    }
}

Traversal meaning visiting all the nodes of a graph. Breadth first Search is also known as Breadth first traversal and is a recursive algorithm for searching all the nodes of a graph or tree data structure.

BFS algorithm
A standard BFS algorithm implementation puts each nodes of the graph or tree into one of two categories:
Visited and
Not Visited

The purpose of the algorithm is to mark each node as visited while avoiding cycles.

The algorithm works as follows:

1. Start by putting any one of the graph's node at the back of a queue or array.
2. Take the front node of the queue and add it to the visited list.
3. Create a list of that node's adjacent nodes. Add the ones which aren't in the visited list to the back of the queue.
4. Keep repeating steps 2 and 3 until the queue is empty.

The graph might have two different disconnected parts so to make sure that we cover every node, we can also run the BFS algorithm on every node

BFS example
Let's see how the BFS algorithm works with an example. We use an undirected graph with 5 nodes.

We start from node 0, the BFS algorithm starts by putting it in the Visited list and putting all its adjacent nodes in the queue.

Next, we visit the element at the front of queue i.e. 1 and go to its adjacent nodes. Since 0 has already been visited, we visit 2 instead.

Node 2 has an unvisited adjacent node in 4, so we add that to the back of the queue and visit 3, which is at the front of the queue.

Only 4 remains in the queue since the only adjacent node of 3 i.e. 0 is already visited. We visit it.

Since the queue is empty, we have completed the Depth First Traversal of the graph.

BFS pseudocode

create a queue Q 
mark v as visited and put v into Q 
while Q is non-empty 
    remove the head u of Q 
    mark and enqueue all (unvisited) neighbours of u

BFS Java code

import java.io.*;
import java.util.*;
 
class Graph
{
    private int numVertices;
    private LinkedList adjLists[];
    private boolean visited[];
 
    Graph(int v)
    {
        numVertices = v;
        visited = new boolean[numVertices];
        adjLists = new LinkedList[numVertices];
        for (int i=0; i i = adjLists[currVertex].listIterator();
            while (i.hasNext())
            {
                int adjVertex = i.next();
                if (!visited[adjVertex])
                {
                    visited[adjVertex] = true;
                    queue.add(adjVertex);
                }
            }
        }
    }
 
    public static void main(String args[])
    {
        Graph g = new Graph(4);
 
        g.addEdge(0, 1);
        g.addEdge(0, 2);
        g.addEdge(1, 2);
        g.addEdge(2, 0);
        g.addEdge(2, 3);
        g.addEdge(3, 3);
 
        System.out.println("Following is Breadth First Traversal "+
                           "(starting from vertex 2)");
 
        g.BFS(2);
    }
}