Generating unique strings with JAVA

If you need randomly generated Strings in your java code you can use the below functions.

01  public String generateRandomString(String s) { 02   try { 03    SecureRandom prng = SecureRandom.getInstance("SHA1PRNG"); 04    String randomNum = new Integer(prng.nextInt()).toString(); 05    randomNum += s; 06    MessageDigest sha = MessageDigest.getInstance("SHA-1"); 07    byte[] result = sha.digest(randomNum.getBytes()); 08    return hexEncode(result); 09   } catch (NoSuchAlgorithmException e) { 10    return  System.currentTimeMillis()+"_"+username; 11   } 12  }

The classical hexEncode method:

01 protected String hexEncode(byte[] aInput) { 02   StringBuffer result = new StringBuffer(); 03   char[] digits = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 04     'a', 'b', 'c', 'd', 'e', 'f' }; 05   for (int idx = 0; idx < aInput.length; ++idx) { 06    byte b = aInput[idx]; 07    result.append(digits[(b & 0xf0) >> 4]); 08    result.append(digits[b & 0x0f]); 09   } 10   return result.toString(); 11  }

Suppose that you need to generate unique random session ids for your logged in users. You can use the above function as follows :

       String sessionId = generateRandomString(username);

10 consecutive calls to generateRandomString("ilkinulas") generates the following strings:

38aca43c835888bc38fbb2d431f537489d637427
8c9fec7eb1309cd60a9548a11b16a30c2cf277a4
d495e83405704d38bfdf1bc3e2a38b31a5b52243
e3f15b900a3b80936596dc4471c0e42889dbf00c
83a4c869593af633a97b3b68433fac19bac7937d
f7573e8fdb4ecf6f58062570b66943b08d87fab8
c19bfdf75abbafbb5d9ca0ce37b90e97f08fccfa
41f0d9cd01ff814f8879bbff4b06642fc01a4624
aae1a792389239ca8db35a1ff9b16856c9921845
c2c9041ab5039b38c79a125c57a10cc6a3eabad9

The power off shell

Linux shell is a powerful tool for developers. Basic commands such as find, grep, diff can be combined to make our lives easier. Suppose that we are working on a project that uses CVS as source code control system, and there are plenty of versions of the same project on CVS. How can you find out the changed java files between version V1 and version V2? The answer is simple: use cvs and diff commands.

First, checkout the two versions of the project in to two different directories. Create a directory named v1. Checkout a version of the source into directory v1.

mkdir v1
cd v1
cvs -d :pserver:ilkinba@192.168.43.12:/usr/local/cvsroot/ina co -rICU_01_03_01 common/InoxCommonUtil


Create a directory named v2. Checkout a version of the source into directory v2.

mkdir v2
cd v2
cvs -d :pserver:ilkinba@192.168.43.12:/usr/local/cvsroot/ina co -rICU_01_03_02 common/InoxCommonUtil

Now it is time to use diff command.

diff -r -q v1/ v2/

This command outputs all the files that differ in directory v1 and v2.
"r" option is used to tell diff command to work recursively.
"q" option is used to tell diff command to work briefly. diff will only write the names of the different files.
Use grep to filter java source files.

diff -r -q v1/ v2/ | grep .java

After detecting the changed java source files you can use diff to see what has been changed in the java source files.

$ diff -r -q v1 v2 |grep .java
Files v1/common/InoxCommonUtil/code/src/com/oksijen/inox/common/util/edr/EDRGenerator.java and v2/common/InoxCommonUtil/code/src/com/oksijen/inox/common/util/edr/EDRGenerator.java differ

$ diff -y --suppress-common-lines v1/common/InoxCommonUtil/code/src/com/oksijen/inox/common/util/edr/EDRGenerator.java v2/common/InoxCommonUtil/code/src/com/oksijen/inox/common/util/edr/EDRGenerator.java

The result of the above command will be something like:

&& st[i].indexOf(label) >= 0) | && st[i].indexOf(fileName) >=

"y" option tells diff to output results in two columns(side by side)
"--suppress-common-lines" option is used to display only changed lines. Common lines will not be displayed.
Thats all.

Search java class files in jars.

This script helps you find the jar file which contains specified java class file.

Usage is simple :

./findClass /home/ilkinulas/lib javax.xml.ws.WebFault

This command searchs all the jars in directory /home/ilkinulas/lib and lists the jars that contain javax.xml.ws.WebFault java class.

#!/bin/bash

START_DIR=$1;
KEYWORD=$2;

for i in `find $START_DIR -name *.jar`
do
       (jar tf $i | grep -q $KEYWORD) && echo $i;
done