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Tomcat6 error: Jar not loaded - Offending class: javax/servlet/Servlet.class

I created a war file and on deployment I encountered this error:

Tomcat6 error: Jar not loaded - Offending class: javax/servlet/Servlet.class

Thankfully, I was able to resolve it easily, as I had the clue where I was going wrong. The war file created using ant build.xml of netbeans used to deploy successfully but the war created using my own build script used to fail during deployment.

The reason for failure was that I was including servlet-api.jar to the war file. This jar offends the tomcat as it already has a copy of it and doesn't expect another.

I modified my war file to success. Below is the snapshot of changes in build.xml

Another important point to note is that ant will expect the servlet-api.jar in classpath at compile time. Hence the servlet-api.jar has to be present in the /lib directory (you cannot delete it). Hence exclude is the best solution. Can't think of any other solution. Please share if you can think of any other.

Spring ResponseBody

When @ResponseBody is applied on a method, it indicates that the return type should be written straight to the HTTP Response Body and not placed in a Model or interpreted as a view name.

#Spring ResponseBody #Spring @ResponseBody #@ResponseBody

Remove unused import in Netbeans

The unused imports can be removed from java class, using any of the following methods:

1. Ctrl + Shift + I

2. Alt + s + o

3. Navigate in Menu (Source -> Fix Import).

The above mentioned process, not only removes the unused import but also add the imports statement, if any missing.

#Remove unused import in Netbeans #How to remove unused import in Netbeans

Spring DisposableBean Usage

Spring DisposableBean is the marker interface for performing action upon spring destruction.

Usage:

import org.springframework.beans.factory.DisposableBean;

public class ABCService implements DisposableBean {

public void destroy() throws Exception {

System.out.println(“Destroying Bean”);

}

The DisposableBean might not exexute if the execution is abruptly terminated using SIGKILL or Ctrl + C

Spring InitializingBean Usage

Spring InitializingBean is the marker interface for performing action upon spring initialization.

Usage:

import org.springframework.beans.factory.InitializingBean;

public class ABCService implements InitializingBean {

public void afterPropertiesSet() throws Exception {

System.out.println("Invoked on Initialization");

}

Load values from properties file in Java

Well, there are couple of ways to load values from properties file in Java. To start with, we will discuss the simplest and most common way of doing it.

Create an instance of File class.

File file = new File("<filelocation>/<filename>");

Create an instance of FileInputObject.

FileInputObject input = new FileInputObject(file);

Create an instance of Properties class from java.util package, which does the real work.

Properties prop = new Properties();

Load the properties to the Properties instance

prop.load(input);

Now, you are good to go.

System.out.println(prop.getProperty("<propname-from-file>));

Let's put it together and into it's shorter form:

Properties prop = new Properties();

prop.load(new FileInputObject("<filelocation>/<filename>"));

System.out.println(prop.getProperty("<propname-from-file>));

Just 3 lines of code and you are done.

One of the limitation of this approach, is that the values are loaded at startup. If you need to update the value, server need to be started.

In the upcoming blogs, we will be discusssing the other approaches.

#java load properties #load properties file java #load value from properties file in java #java properties #java configuration

Remove the last/first occurance of delimiter

Many a times we need to loop through collection & form a string delimited by some character. But when we loop, if always end up with an extra delimiter, either at start or in the end. I also landed in a similar situation and started pondering over the possible & best solution.

Use StringBuffer instead of String & remove the extra character using deleteCharAt() method:

sb.deleteCharAt(sb.length() - 1)

Another way can be, to handle it while looping:

String delimiter = "";

for(String str : StringList) {

sb.append(delimiter);

delimeter = ",";

sb.append(str)

}

Another can be reducing the lenght by 1:

sb.setlength(sb.lenght() - 1);

subString() method of String class:

str.subString(0, str.length() - 1);

#java string #remove the last occurance of character #remove the last occurance of delimiter

One road leads to many others. How true!

Calculate Execution time in Java

Following is the easiest way to find the execution time of a code block:

1. Get the start time before the code block:

long startTime = System.currentTimeMillis();

2. Get the end time after the code block:

long endTime = System.currentTimeMillis();

3. Calculate the time difference:

long secsTaken = (endTime - startTime); // unit is millisecond

4. Convert to required unit (Eg: Second):

long secsTaken =secsTaken / 1000;

#java execution time #java #java time difference #calculate execution time

Solr Tokenizer

Tokenizer is an analyzer that takes text and splits it into smaller units.

Eg:

"Hello World" => "Hello","World" (Tokenized on whitespace, generated 2 tokens)

Some of the commonly used tokenizer are mentioned below:

WhitespaceTokenizerFactory: Tokenizes on whitespace. Above is the example of this factory.

KeywordTokenizerFactory: This doesn't do any tokenization but returns as it is. Is is needed when you want to perform exact match.

StandardTokenizerFactory: This analyzer has the most practical use. It tokenizes on whitespace, special characters etc. Please refer the apache site for detailed description.

There are several other tokenizers like LetterTokenizerFactory, HTMLStripWhitespaceTokenizerFactory etc.

#solr #tokenizer #WhitespaceTokenizerFactory #KeywordTokenizerFactory #StandardTokenizerFactory

Center align a div

To align a div to the center of page, here lies the magic:

margin:0 auto;

Ensure that you set the width of the page, else it will align only vertically.

#css #center align #div #css margin

Fewer the choice, happier is the life!

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