Java Snippets

Surround Strings with Quotes

2011-05-13T13:29:00.000-07:00

The following Java class adds quotes to a string depending on
whether it is a number or not. The class relies on the NumberFormatException to determine whether a string is a number.
The added benefit is that single quotes in strings are escaped with a backslash.

public class Util {
 public static String escapeQuotes( String s ){
      return s.replaceAll("'","\\\\'");
 }
 private static boolean isNumber(String str){
  try{
   Integer.parseInt(str);
   return true;
  }
  catch(NumberFormatException e){
   return false;
  }
 }
 private static boolean isEmpty(String str){
  return !(str.length()>0);
 }
 public static String addQuotes(String str) {
  str = str.trim();
  if(!isEmpty(str)){
   if(isNumber(str))
    return str;
   else
    return "'"+ escapeQuotes(str)+"'";
  }
  else
   return null;
 }

 public static String deleteLastCharacter(String str){
   return str.substring(0, str.length()-1);
 }
}

This class could be used as a helper class to construct a valid sql statement.
Here is code for a method that takes file contents and adds single quotes around Strings leaving numbers intact:

public static void convert (BufferedReader in, PrintWriter out)
   throws IOException {
 String separator  = System.getProperty("line.separator");
 String delimiter  = ",";
 for (String line = in.readLine(); line != null; line = in.readLine()) {
  line = line.trim();
  if (line.length() == 0) {
   continue;
  }
  StringTokenizer st = new StringTokenizer(line, delimiter, false);
  String outLine ="";
  while(st.hasMoreTokens()) {
   String token  = st.nextToken();
   outLine += Util.addQuotes(token) +",";
  }
  outLine = Util.deleteLastCharacter(outLine);
  out.print(outLine + separator);
  }
 in.close();
 out.close();
}

As you can see, this method accepts 2 arguments, BufferedReader and PrintWriter. It takes each line in a file and splits it into
comma-separated tokens. Then, addQuotes() method is called on each token. The line is assembled again and written to a PrintWriter.

Java Text File Splitter Class

2011-05-13T13:27:00.001-07:00

Here is a Java class that splits a text file into multiple files using a supplied string as a separator.

It accepts two arguments in the constructor: a path to the file, and a token to be used for separation.

Usage example:

TextFileSplitter tfs = new TextFileSplitter('myfile.txt', 'Section');
tfs.run();

It will create a sub-directory in the same directory as the file where it will place the resulting files.

This is a very basic version that does not throw any exceptions.


import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Iterator;

public class TextFileSplitter {

 private static String fullPath ;
 private static String token;

 public TextFileSplitter(String path, String token) {
  this.fullPath = path;
  this.token = token;
 }


 public void run(){

  ArrayList al = splitIntoTokens(fullPath, token);

  if(al.size()==0){
   return;
  }
  String dir = getDirectoryFromFileName(fullPath);

  int pageIndex =1;
  Iterator iter = al.listIterator();
  String name = getFileName(fullPath);

  while(iter.hasNext()){
   String str = (String)iter.next();
   String fileName = dir+"\\"+ name + "_"+ pageIndex + ".txt";
   try {
    System.out.println(fileName);
    writeFile(fileName, str);
   }
   catch (IOException e) {
    e.printStackTrace();
   }
   pageIndex++;
  }
 }


 private String getFileName(String path){

  String fileName = null;
  String separator = File.separator;

  int pos = path.lastIndexOf(separator);
  int pos2 = path.lastIndexOf(".");

  if(pos2>-1)
   fileName =path.substring(pos+1, pos2);
  else
   fileName =path.substring(pos+1);

  return fileName;
 }

 private String getDirectoryFromFileName(String fname) {

  String parent =  (new File(fname).getParent());

  String name = getFileName(fname);

  String dirPath = parent+"\\" + name;

  File dir = new File(dirPath);

  if(!dir.exists()){
   boolean success = dir.mkdir();
   if (!success) {
    System.out.println("Directory creation failed");
    return null;
   }
  }
  return dirPath;
 }




 private  void writeFile(String fname, String str) throws IOException{
  BufferedWriter out=new BufferedWriter ( new FileWriter(fname));
  out.write(str);
  out.close();
 }
 
 //splits a file into an ArrayList of strings using the separator passed
 
 private ArrayList splitIntoTokens(String fname, String token){
  String line;
  StringBuffer sb = new StringBuffer();
  ArrayList al = new ArrayList();
  String lineSeparator =  System.getProperty("line.separator");
  try {
   FileInputStream fis = new FileInputStream(fname);
            BufferedReader reader=
              new BufferedReader
                (new InputStreamReader(fis));

            while((line = reader.readLine()) != null) {
    if((line.indexOf(token))>-1){
     al.add(sb.toString());
     sb = new StringBuffer();
    }
    sb.append(line + lineSeparator);
   }
            //add last section
            al.add(sb.toString());
   reader.close();
  }
  catch (IOException e) {
            System.err.println("*** IOexception ***" + e.getMessage());
  }
  return al;

 }
}

List Files in a Directory

2011-05-13T13:25:00.001-07:00

The following Java example returns an ArrayList of only those files that have a .csv extension.

public static ArrayList listFiles(String dirName) {
 ArrayList al = new ArrayList();
 File dir = new File(dirName);

 String[] children = dir.list(filter);
 if (children == null) {
//Either dir does not exist or is not a directory
  }
 else {
  for (int i = 0; i < children.length; i++) {
  // Add the file name to ArrayList
   al.add(children[i]);
  }
 }
  return al;
}

// Create an an inner class that implements the FilenameFilter interface.
    static FilenameFilter filter = new FilenameFilter() {
        public boolean accept(File dir, String name) {
            return name.endsWith("csv");
        }
    };

To list all files in the directory use the list() method without arguments.

The code is based on the Java Developers Almanac .

Read File Contents into Java ArrayList

2011-05-13T13:24:00.001-07:00

The following method reads file contents into an ArrayList. Each element of the ArrayList will contain a line from the file.

public ArrayList readFile(String fname){
    String line;
    StringBuffer sb = new StringBuffer();
    ArrayList al = new ArrayList();
    try {
     FileInputStream fis = new FileInputStream(fname);
        BufferedReader reader=
          new BufferedReader
            (new InputStreamReader(fis));
        while((line = reader.readLine()) != null) {
   al.add(line);
  }
        reader.close();
 }
 catch (IOException e) {
     System.err.println("*** IOexception ***" + e.getMessage());
 }
 return al;
 }

Get File Name without extension from Its Path

2011-05-13T13:23:00.001-07:00

The following Java method returns a file name without extension from its path.

public static String getFileName(String path){

 String fileName = null;
 String separator = File.separator;

 int pos = path.lastIndexOf(separator);
 int pos2 = path.lastIndexOf(".");

 if(pos2>-1)
  fileName =path.substring(pos+1, pos2);
 else
  fileName =path.substring(pos+1);

 return fileName;
}

Create Sub-Directory From File Name in Java

2011-05-13T13:21:00.000-07:00

Description:
You have a file name and you need to create a new directory in the folder where the file resides.

Solution:

The following method creates a new directory in the same directory as the file. If the directory exists already, it does nothing.
In other words, it makes sure the directory is there.
It accepts two strings as arguments, file name and sub-directory name.

boolean  createDirectory (String fname, String dirName) {
 //get the path to the parent directory
 String parent =  (new File(fname).getParent());
 //construct a new directory path
 String dirPath = parent+"\\" + dirName;

 File dir = new File(dirPath);

 if(!dir.exists()){
  boolean success = dir.mkdir();
  if (!success) {
   System.out.println("Directory creation failed");
   return false;
  }
 }
 return true;
}

A variation of the above method is the one that returns the path to the sub-directory:

public static String getDirectory(String fname, String dirName) {

  String parent =  (new File(fname).getParent());
  String dirPath = parent+"\\" + dirName;
  File dir = new File(dirPath);

  if(!dir.exists()){
   boolean success = dir.mkdir();
   if (!success) {
    System.out.println("Directory creation failed");
    return null;
   }
  }
  return dirPath;
 }

Another thing we could do is have the method create a sub-directory based on the file name without extension.

public static String getDirectoryFromFileName(String fname) {

  String parent =  (new File(fname).getParent());
  //extract a file name without extension from the path
  String name = getFileName(fname);
  String dirPath = parent+"\\" + name;

  File dir = new File(dirPath);

  if(!dir.exists()){
   boolean success = dir.mkdir();
   if (!success) {
    System.out.println("Directory creation failed");
    return null;
   }
  }
  return dirPath;
 }

Remove Duplicates in Java

2011-05-13T13:18:00.001-07:00

Description:
You have an ArrayList with duplicates, and you need to remove them

Solution:

Create a HashSet with the ArrayList as the constructor argument:
```
HashSet hashSet = new HashSet(myArrayList);
```

If the order is important, use a LinkedHashSet:

LinkedHashSet  linkedHashSet = new LinkedHashSet(myArrayList);

Use the following method to remove duplcates:

static ArrayList deDupKeepingFirst(ArrayList withDups,
  Comparator comparator,boolean presorted) {
 if (!presorted) {
  Collections.sort(withDups, comparator);
 }
 int size = withDups.size();

 ArrayList result = new ArrayList(size);
 if (size <= 1) {
  if (size == 1) {
   result.add(withDups.get(0));
  }
  return result;
 }
 Object prev = withDups.get(0);
 result.add(prev);

 for (int i = 1; i < size; i++) {
  Object o = withDups.get(i);
  if (comparator.compare(o, prev) != 0) {
   result.add(o);
   prev = o;
  }
  else
   System.out.println(o.toString());
 }
 return result;
}

private static class StringComp implements Comparator
{
 public int compare(Object o1, Object o2)
 {
  return o1.toString().compareToIgnoreCase((o2).toString());
 }
}

Sorting ArrayLists in Java

2011-05-13T13:15:00.000-07:00

Description:
You have an ArrayList of objects that you need to be sorted by their
integer member variables

Solution:

Let's say you have a Record class with the following members: int id, int weight;

class Record {
 public Record(int i, int w){
  this.id =i;
  this.weight = w;
 }
 int id;
 int weight;

 public int getId() {
  return id;
 }
 public int getWeight() {
  return weight;
 }
}

You have an ArrayList of objects of the Record class that need to be sorted by weight. To make it possible, the Record class needs to implement the Comparable interface which mandates the use of the compareTo method with the following signature:

public int compareTo(Object o)

That means we need to add the following code to the Record class:

public int compareTo(Object o) {
 int weight = ((Record) o).getWeight();
 return weight - this.weight;
}

We use weight - this.weight for descending order and
this.weight - weight for ascending order.

Once we have the proper method in the Record class, all we need to do is use the sort method
of the Collections class.

Collections.sort (myArrayList);

Determine the Next Month in Java

2010-05-25T15:24:00.000-07:00

First, get an instance of the Calendar class:

Calendar cal = GregorianCalendar.getInstance();

Declare a format to be used:

SimpleDateFormat df = new SimpleDateFormat("MMM yyyy");

Set the Calendar's current time to today's Date:

cal.setTime(new Date());

Add a month to the Calendar's date:

cal.add(Calendar.MONTH, 1);

Format the new date into a string:

String nextMonth = df.format(cal.getTime());

The nextMonth String will contain the next month's value.

The following technique allows us to show 12 consecutive months:

cal.setTime(new Date());
for(int i=0; i<12;i++){
   cal.add(Calendar.MONTH, 1);
   String nextMonth = df.format(cal.getTime());
   System.out.println(nextMonth);
}

The Calendar class has a lot of other methods to set its date. For example, you can set the year and month as follows:

cal.set(Calendar.YEAR, 2010);
cal.set(Calendar.MONTH, 05);

cal.set(Calendar.MONTH, Calendar.JUNE);

This code sets the Calendar date to June 2010.

You can also set the date using year, month, and day arguments.

cal.set(2010, 05, 15);

This code sets the Calendar date to June 15, 2010.

Enumerate All Keys of a Hashtable

2010-05-24T19:46:00.000-07:00

Set keys = myHashTable.keySet();
Iterator iter = keys.iterator();
while (iter.hasNext())
{
    Object key = iter.next();
    System.out.println("key:"+ (String)key);
}

A Simple Way to Find Data in XML Using dom4j

2010-05-24T19:42:00.000-07:00

dom4j is a small but powerful package to parse XML documents. It has the advantage of having a very small footprint and being very easy to use. The dom4j website has a lot of examples that show how to use it.
If you have a simple xml file like the following one, I will show you how to use dom4j to find data.

<?xml version="1.0"?>
<students>
        <student>
                <name>Mike</name>
                <course>JSP</course>
        </student>
        <student>
                <name>Janet</name>
                <course>EJB</course>
        </student>
</students>

The file name is students.xml.
Suppose, you need to find the course for a student named Mike.
First, you need to parse a document:

public Document parse(String file) throws DocumentException {
    SAXReader reader = new SAXReader();
    Document document = reader.read(file);
    return document;
}

Document doc= parse("students.xml");

Then, use the following statement:

String course = doc.valueOf("//student[name='Mike']/course");

This statement uses an XPath Engine library from Jaxen which means you need to have it in your classpath.
If you want to limit your library usage to dom4j proper you'll have to write your own method which may look like the following:

public String findStudentCourse(Document doc, String studentName) {
    Element root = doc.getRootElement();
    for (Iterator i = root.elementIterator(); i.hasNext();) {
        Element el = (Element) i.next();
        if (el.elementText("name").equals(studentName)) {
            return el.elementText("course");
        }
    }
    return null;
}

If you want to iterate through all the student elements and print the name-course combinations use the following example:

Element root = document.getRootElement();
for (Iterator i = root.elementIterator(); i.hasNext();) {
    Element el = (Element) i.next();
    System.out.println("Child Element Path :" + el.getPath());
    System.out.println("    Name:" + el.elementText("name"));
    System.out.println("    Course:" + el.elementText("course"));
}

Convert Collection to Array

2010-05-24T19:30:00.000-07:00

The following example converts an ArrayList into an array of strings:

    ArrayList al = new ArrayList();
    //Fill the array 
    ...........

    String[] aStrings = (String[]) al.toArray(new String[0]);

Find and Replace All Occurrencies of a String

2010-05-24T19:13:00.000-07:00

Description:
You need to replace all occurencies of a string in a text file

Solution: (For Java 1.4 and higher) '

public static void readReplace(String fname, String oldPattern, String replPattern){
    String line;
    StringBuffer sb = new StringBuffer();
    try {
        FileInputStream fis = new FileInputStream(fname);
        BufferedReader reader=new BufferedReader ( new InputStreamReader(fis));
        while((line = reader.readLine()) != null) {
            line = line.replaceAll(oldPattern, replPattern);
            sb.append(line+"\n");
        }
        reader.close();
        BufferedWriter out=new BufferedWriter ( new FileWriter(fname));
        out.write(sb.toString());
        out.close();
    }
    catch (Throwable e) {
                System.err.println("*** exception ***");
    }
}

Transfer data from Excel to Access through Java

2010-05-24T14:35:00.000-07:00

This is sample code that shows how to use Java to transfer data from Excel spreadsheets to Access. The basic idea is to create an ODBC data source for both Excel and Access. Then use the JDBC API to retrieve records from the Excel ODBC source and insert them to Access.
The Excel ODBC source is represented by "jdbc:odbc:BulkMail", and the Access ODBC source is represented by "jdbc:odbc:Whisky" in the code.

import java.sql.*;
public class ExcelToAccess {
public static void main (String[] args)
{
try
{
Class.forName ("sun.jdbc.odbc.JdbcOdbcDriver");
String sourceURL = "jdbc:odbc:BulkMail";
String sourceAccess = "jdbc:odbc:Whisky";
Connection dbConnection = DriverManager.getConnection(sourceURL);
Connection dbAccess = DriverManager.getConnection(sourceAccess);
String comp;
String fax;
Statement st = dbConnection.createStatement();
Statement stAccess = dbAccess.createStatement();
ResultSet rs = st.executeQuery("Select LastName, FirstName, Company, FaxNumber from Customers");
while (rs.next()){
    comp = rs.getString ("Company");
    fax = rs.getString ("FaxNumber");
    stAccess.executeUpdate("INSERT INTO Company (CompanyName, FaxNumber) VALUES('"

+ comp + "','" + fax + "')");
}
rs.close();
dbConnection.close();
dbConnection =null;
dbAccess.close();
dbAccess = null;
}
catch(SQLException sqle)
{ System.err.println(sqle); }
catch(ClassNotFoundException cnfe)
{ System.err.println(cnfe); }
}

}