Strait Fram Singapuur

In almost all real world projects (non Spring + We are not considering Arquillian or any similar framework) where you are using JPA (Hibernate implementation), the data source binding happens by JNDI and the services are provided by EJBs, which means to test your entities for any CRUD operation you have to deploy the bundle (ear, ejb or war) into the application server which adds time to your development efforts each time you make any change. So in this post we will see how we can temporarily inject entity manager into your business class so that you can test all the operations you want to perform on entities without deploying the application or restarting server quite often.

persistence.xml: The configuration for entity managers both inside an application server and in a standalone application reside in a persistence archive. In the next section we focus on standalone configuration.

 
  org.hibernate.ejb.HibernatePersistence
  com.gognamunish.test.Entity
  
   
   
   
   
   
  
 

Please Note:

• The database dialect we have chosen is MySQL for obvious reasons.
• Persistence unit has name test_unit and the type is RESOURCE_LOCAL and not JTA.
• com.gognamunish.test.Entity is the entity which we want to test later.
• As we are running without a JNDI available datasource, we must specify JDBC connections with Hibernate specific properties

Next in your business class you can get reference to the entity manager as follow:

EntityManagerFactory factory ;
factory = Persistence.createEntityManagerFactory("test_unit");
EntityManager manager = factory.createEntityManager();

That's all you need , after obtaining the reference focus only on your entity and the operation you want to perform on it.
Let's try one sample example:

/* Sample Entity class */
@javax.persistence.Entity
@Table(name = "Entity")
public class Entity {
 @Id
 private Long id;
 @Column
 private String value;
}

package com.gognamunish.test;

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

/**
 * Sample Test - nothing fancy.
 * 
 * @author Munish Gogna
 * 
 */
public class LocalEntityManager {
 static EntityManager manager;
 static {
  EntityManagerFactory factory = Persistence
    .createEntityManagerFactory("test_unit");
  manager = factory.createEntityManager();
 }

 public static void main(String[] args) {

  System.out.println("Before Entities: " + getEntities());

  manager.getTransaction().begin();
  Entity entity = new Entity();
  entity.setId(1l);
  entity.setValue("my first value");
  saveOrUpdate(entity);
  manager.getTransaction().commit();

  System.out.println("After Entities: " + getEntities());

 }

 private static Entity saveOrUpdate(Entity entity) {
  return manager.merge(entity);
 }

 @SuppressWarnings("unchecked")
 private static List<Entity> getEntities() {
  return manager.createQuery("from Entity").getResultList();
 }
}

LOGS:
Hibernate: select entity0_.id as id0_, entity0_.value as value0_ from Entity entity0_
Before Entities: []
Hibernate: select entity0_.id as id0_0_, entity0_.value as value0_0_ from Entity entity0_ where entity0_.id=?
Hibernate: insert into Entity (value, id) values (?, ?)
Hibernate: select entity0_.id as id0_, entity0_.value as value0_ from Entity entity0_
After Entities: [Id:1, Value:my first value]

One of the frequently asked questions in interviews, let's try few ways available in JDK to reverse a string:

import java.util.Stack;
public class StringReverse {

 public static String reverse1(String s) {
  int length = s.length();
  if (length <= 1)
   return s;
  String left = s.substring(0, length / 2);
  String right = s.substring(length / 2, length);
  return reverse1(right) + reverse1(left);
 }

 public static String reverse2(String s) {
  int length = s.length();
  String reverse = "";
  for (int i = 0; i < length; i++)
   reverse = s.charAt(i) + reverse;
  return reverse;
 }

 public static String reverse3(String s) {
  char[] array = s.toCharArray();
  String reverse = "";
  for (int i = array.length - 1; i >= 0; i--)
   reverse += array[i];

  return reverse;
 }

 public static String reverse4(String s) {
  return new StringBuffer(s).reverse().toString();
 }

 public static String reverse5(String orig) {
  char[] s = orig.toCharArray();
  int n = s.length - 1;
  int halfLength = n / 2;
  for (int i = 0; i <= halfLength; i++) {
   char temp = s[i];
   s[i] = s[n - i];
   s[n - i] = temp;
  }
  return new String(s);
 }

 public static String reverse6(String s) {

  char[] str = s.toCharArray();

  int begin = 0;
  int end = s.length() - 1;

  while (begin < end) {
   str[begin] = (char) (str[begin] ^ str[end]);
   str[end] = (char) (str[begin] ^ str[end]);
   str[begin] = (char) (str[end] ^ str[begin]);
   begin++;
   end--;
  }

  return new String(str);
 }

 public static String reverse7(String s) {
  char[] str = s.toCharArray();
  Stack<Character> stack = new Stack<Character>();
  for (int i = 0; i < str.length; i++)
   stack.push(str[i]);

  String reversed = "";
  for (int i = 0; i < str.length; i++)
   reversed += stack.pop();

  return reversed;
 }

}

Feel free to suggest other ways if you have.

My previous post was about merging the PDF files into single file using PDFBox, the limitation of that approach was if you had fill able form inside any PDF file it was lost, to over come that issue here is an updated version of the same post using iText library.

import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
import java.util.Set;

import com.lowagie.text.pdf.AcroFields;
import com.lowagie.text.pdf.PdfCopyFields;
import com.lowagie.text.pdf.PdfReader;

/**
 * Merges the PDF files while retaining the fillable forms within them. It also
 * renames form field (to avoid conflicts) which can have an impact if form is
 * submitted to server but for printing purpose should be OK.
 * 
 * @author Munish Gogna
 * 
 */
public class PDFMerge {
 private static int counter = 0;

 public static void merge(List<InputStream> sourcePDFs,
   OutputStream targetPDF) throws Exception {
  if (sourcePDFs != null && targetPDF != null) {
   PdfCopyFields copy = new PdfCopyFields(targetPDF);

   for (InputStream stream : sourcePDFs) {
    PdfReader pdfReader = new PdfReader(stream);
    renameFields(pdfReader.getAcroFields());
    copy.addDocument(pdfReader);
    stream.close();
   }
   copy.close();
  }
 }

 private static void renameFields(AcroFields fields) {
  Set<String> fieldNames = fields.getFields().keySet();
  String prepend = String.format("_%d.", counter++);

  for (String fieldName : fieldNames) {
   fields.renameField(fieldName, prepend + fieldName);
  }
 }

 public static void main(String[] args) {
  try {
   List<InputStream> pdfs = new ArrayList<InputStream>();
   pdfs
     .add(new URL(
       "http://thewebjockeys.com/TheWebJockeys/Fillable_PDF_Sample_from_TheWebJockeys_vC5.pdf")
       .openStream());
   pdfs
     .add(new URL(
       "http://help.adobe.com/en_US/Acrobat/9.0/Samples/interactiveform_enabled.pdf")
       .openStream());
   OutputStream output = new FileOutputStream("merged.pdf");

   merge(pdfs, output);

  } catch (Exception e) {
   e.printStackTrace();
  }
 }

}

The iText jar can be downloaded here

Thanks.