How To Resolve Java.Lang.Classnotfoundexception Inward Java

What is ClassNotFoundException inwards Java
ClassNotFoundException is i of Java nightmare every Java developer human face upward inwards at that topographic point 24-hour interval to 24-hour interval life. java.lang.NoClassDefFoundError in addition to java.lang.ClassNotFoundException are 2 errors  which occurs past times in addition to at i time in addition to chew upward of your precious fourth dimension piece finding in addition to fixing rootage cause. From the mention java.lang.ClassNotFoundException looks quite uncomplicated but underlying movement of it is ever unlike and which classifies it every bit an environmental issue. In this coffee tutorial nosotros volition see what is ClassNotFoundException inwards java, what is existent movement of it and how to prepare it along amongst roughly to a greater extent than frequent in addition to infamous examples of java.lang.ClassNotFoundException inwards Java or J2EE, Don’t mistake this exception amongst NoClassDefFoundError inwards Java which is too due to wrong classpath inwards Java.  Though both of them are related to missing cast file when Java tries to charge cast inwards Java they are completely unlike to each other.  Correct agreement of  When cast is loaded inwards Java in addition to How Classpath works  is must to troubleshoot in addition to prepare this error quickly.

What is java.lang.classNotFoundException inwards Java

As the mention suggests classNotFoundException in Java is a subclass of java.lang.Exception in addition to Comes when Java Virtual Machine tries to charge a detail cast in addition to doesn't establish the requested cast inwards classpath. Another of import signal close this Exception is that, It is a checked Exception in addition to yous take to render explicitly Exception treatment piece using methods which tin perhaps throw classnotfoundexception inwards coffee either past times using try-catch block or past times using throws clause. Though underlying concept of this exception is uncomplicated but it ever manifest itself inwards such format that yous take to pass roughly fourth dimension to figure out what precisely wrong amongst your classpath. If yous desire to know nasty secrets of coffee classpath  which tin movement upshot consider the link. 

When ClassNotFoundException occurs inwards Java:

As per java MD java.lang.classNotFoundException comes inwards next cases:

1) When nosotros endeavor to charge a cast past times using Class.forName() method in addition to .class file or binary of cast is non available inwards classpath.
2) When Classloader try to charge a cast past times using findSystemClass () method.
3) While using loadClass() method of cast ClassLoader in Java.

Reflection is non bad ability of Java but yous take to last aware of java.lang.classNotFoundException piece using it or loading cast inwards Java. See Understanding the Java Virtual Machine: Class Loading in addition to Reflection to larn to a greater extent than close how precisely cast loading plant within JVM.

Examples of classnotfoundexception inwards java

Though java.lang.classNotFoundException is really mutual in addition to it tin come upward for whatever classes, I unremarkably consider it piece doing JDBC connectivity similar when I was writing Java programme to connect Oracle database. I am going to listing roughly of the most mutual scenario where yous volition acquire classnotfoundexception inwards java.

java.lang.classnotfoundexception com.mysql.jdbc.driver

This is classical in addition to most infamous illustration of  in addition to too my kickoff consider with java.lang.ClassNotFoundException in addition to comes when yous are writing JDBC connectivity code in addition to trying to charge the JDBC driver. In this detail instance of ClassNotFoundException looks similar mysql driver jounce file is missing from Classpath. If yous pay attending yous volition uncovering that nosotros purpose method Class.forName (“driver”) to charge the driver cast which resides inwards a detail jounce inwards instance of this its mysql-connector.jar in addition to if that jounce is non inwards classpath or non accessible to JVM it volition throw  java.lang.ClassNotFoundException: com.mysql.jdbc.Driver

Here are few to a greater extent than infamous examples of java.lang.ClassnotFoundException which comes hither in addition to at that topographic point piece doing whatever Java J2EE project. 

java.lang.classnotfoundexception org.hibernate.hql.ast.hqltoken

java.lang.classnotfoundexception org.springframework.web.context.contextloaderlistener

java.lang.classnotfoundexception org.eclipse.core.runtime.adaptor.eclipsestarter

java.lang.classnotfoundexception org.apache.catalina.startup.catalina

java.lang.classnotfoundexception javax.mail.messagingexception

java.lang.classnotfoundexception oracle.jdbc.driver.oracledriver

This ClassNotfoundException comes when yous are trying to connect Oracle database from Java programme using JDBC but yous don't receive got corresponding Oracle driver e.g.ojdbc6.jar is non inwards classpath of your Java program

More Complicated ClassNotFoundException

With the advent of dynamic library e.g. OSGi and ClassLoader inwards Java, this exception tin last to a greater extent than tricky in addition to difficult to find. Thanks to Mr. Anonymous who has summarized this beautifully, hither it is what he says

“It tin acquire a flake to a greater extent than complicated than that. In truth a cast does non receive got to last just visible past times the JVM through its classpath, but last visible past times the Classloader being used. When yous are inwards a multi-classloader environment (In a EE environment, for example, but non express to), each classloader may receive got its ain rules to search for the classes, in addition to this demeanour powerfulness depend on the dynamic hierarchy of the Classloaders.

For example, inwards a projection that uses an EAR packaging amongst WARs within it, libraries inwards the lib folder of the EAR are visible to classes within a WAR, but whatever classes packaged inwards a jounce position inwards the WEB-INF/lib on the WAR cannot last seen past times classes inwards unlike modules (other WARs, EJB-JARS, etc).

It tin acquire actually complicated every bit its mutual for unlike modules depending on unlike versions of the same libraries every bit unlike modules depend on each other. It tin last a challenge to care this. Sometimes the classloader can consider multiple versions of the same class; sometimes they tin consider no version at all. Sometimes unlike dependency paths halt inwards unlike versions of the same class. And many of this cases halt inwards a ClassNotFoundException.

And in addition to thus nosotros receive got OSGi... “. If a cast is non visible to ClassLoader than it tin too throw NoClassDefFoundError in Java every bit explained in  3 ways to resolve NoClassDefFoundError inwards Java.

How to prepare java.lang.ClassNotFoundException inwards Java
As yous receive got seen from inwards a higher house examples its clear work of classpath, thus hither is my approach to prepare or resolve java.lang.ClassNotFoundException:

1) First uncovering out the jounce file on which problematic cast file is introduce for illustration inwards instance of "com.mysql.jdbc.driver" its mysql-connector-java.jar. If yous don't know how to uncovering which jar file a detail cast yous tin consider eclipse shortcuts to practise that or yous tin but practise "Ctrl+T" inwards Eclipse in addition to type the mention of class, It volition listing all the jounce inwards the fellowship they appear inwards eclipse classpath.

2) Check whether your classpath contains that jar, if your classpath doesn't incorporate the jounce in addition to thus just add together that cast inwards your classpath.

3) If it’s introduce inwards your classpath in addition to thus at that topographic point is high peril that your classpath is getting overridden or application is using classpath specified inwards jounce file or start-up script in addition to to prepare that yous take to uncovering the exact classpath used past times your application.


Live illustration of reproducing in addition to Fixing ClassNotFoundException inwards java
I remember if nosotros are able to reproduce in addition to solve sure enough work nosotros acquire to a greater extent than comfortable dealing amongst that, that’s why hither nosotros volition reproduce java.lang.ClassNotFoundException and solve it past times next the concept nosotros receive got discussed thus far.

1) Create a Class called StockTrading.java

public cast StockTrading{
   populace String getDescription(){
   render "StockTrading";
  }
}

2) create a Class called OnlineStockTranding.java in addition to charge the cast StockTrading.java every bit Class.forName ("stocktrading");

public cast OnlineStockTrading {
   populace static void main(String args[]) throws ClassNotFoundException{
      Class.forName("StockTrading");
      System.out.println("StockTrading cast successfully loaded");
   }
}

3) Compile both Java source file which volition practise 2 cast files in addition to run the programme should run fine.

javin@trading /java: javac *.java

javin@trading /java: ls –lrt
-rw-r--r-- 1 javin None  xc Aug 21 09:27 StockTrading.java
-rw-r--r-- 1 javin None 208 Aug 21 09:28 OnlineStockTrading.java
-rwxr-xr-x 1 javin None 282 Aug 21 09:28 StockTrading.class
-rwxr-xr-x 1 javin None 638 Aug 21 09:28 OnlineStockTrading.class

javin@trading /java:$ java OnlineStockTrading
StockTrading cast successfully loaded


4) Now just remove the .class file for stocktrading.java in addition to run the Java program in addition to it volition throw java.lang.ClassNotFoundException inwards java.

javin@trading /java: rm StockTrading.class

javin@trading /java: java OnlineStockTrading
Exception inwards thread "main" java.lang.ClassNotFoundException: StockTrading
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)


ClassFoundException vs NoClassDefFoundError vs UnSupportedClassVersionError
There are lots of exceptions inwards coffee but these iii are the i who most haunted the coffee developer most mainly because these iii are generally related to surround issues in addition to they all depends upon JVM in addition to Classpath behaviour. Though they await similar at that topographic point is slight difference betwixt ClassFoundException in addition to NoClassDefFoundError in addition to UnSupportedClassVersionError in addition to nosotros volition highlight those differences hither for slowly agreement in addition to differentiating these three:

1) ClassNotFoundException comes on Runtime when requested cast is non available inwards classpath in addition to mainly due to telephone vociferation upward to Class.forName () or Classloader.loadClass () or ClassLoader.findSystemClass ().

2) NoClassDefFoundError comes when problematic cast was introduce when your compiled your application but they are non inwards classpath piece yous running your program.

3) UnSupportedClassVersionError is slowly to differentiate because it’s related to version of classpath in addition to unremarkably comes when yous compile your code inwards higher Java version in addition to endeavor to run on lower coffee version. Can last resolved but past times using i coffee version for compiling in addition to running your application.

So that's all on ClassNotFoundException inwards java for at i time , delight allow me know if yous receive got whatever tip or  whatever personal sense on solving java.lang.ClassNotFoundException inwards Java which yous would similar to share.

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