Why class.forName to load driver

hi all,
as most of the times the loading of jdbc driver is carried out
by using the function class.forName, Why so ?
as i tryied with creating the object of the driver class like
Object driver = new <JDBC DRIVER>;and the code worked fine
so is there any difference in the two methods of loading the
drivers ?
if not wot is the use of method class.forname ?
thanx

That 's fine, but what if you change database back end in near future.
I will define a property and used class.forName ("read property").
In your case, you have to change the code about loading the JDBC driver as well.
Using std. JDBC API functionality and loading driver dynamically, leaves some of the part of the code that are not a candidate for a change in case back-end DB is changed.
BS

Similar Messages

Why Class.forName is used to load the driver ?

Hi all,
Why Class.forName() is used to load the driver ?. Can I use any other method to load the driver safely ?.
rgds
Antony Paul

That's still redundant. Sure, it works. Here are some equivalent forms:
    new MySqlDriver();
    DriverManager.registerDriver(new MySqlDriver());
    New LinkedList().add(new MySqlDriver());
    if (new MySqlDriver() == new MySqlDriver())
        System.out.println("department of redundancy department");
    Driver unusedVariable[] = new Driver[] { new MySqlDriver() };
    Class anotherUnusedVariable = MySqlDriver.class; // I'm not 100% sure this works
    new File(new MySqlDriver().toString());
    while (new MySqlDriver() == null)
    new Double(Math.sqrt(new MySqlDriver().toString().length()) / 42);

Error class not found with Class.forName("oracle.jdbc.driver.OracleDriver")

sorry Got the solution...!!!!
Hi
I am trying to connect to oracle database on the server, oracle client installed on working m/c, I have placed classes111.zip (from oracle 8) in jdk1.1.8demojrelibext folder and I have set the classpath to the ext folder. The code
try
Class.forName("oracle.jdbc.driver.OracleDriver");
catch(Exception e)
when I run this code , error as
[[ java.lang.ClassNotFoundException: oracle.jdbc.driver.OracleDriver ]]
Please reply what are settings I should to to load this oracle driver,
Thanks
Mayank
Message was edited by:
user560333

I currently have this same problem. How did you solve yours see my post Cant find suitable driver.

Why Class.forName("driver class") ?

Hi,
whay we are using Class.forName("driver class"). why we dont import the driver package and access the required classes and methods?
for eg:
insead of calling
Class.forName("com.microsoft.jdbc.sqlserver.SQLServerDriver"); ,can we use import com.microsoft.jdbc.sqlserver.*; ?
what is the use of DriverManager in this context? any connection between DriverManager and Class.forName() ?
expecting answers.

sure you can import the packages and use the classes directly but that defeats the whole purpose of pluggable drivers.
Class.forName causes the class to be loaded and as stated before that should cause the driver to register itself with the driver manager.
so then if you have a system where you are talking to several different database vendors then you don't have to worry about which is which as the DriverManager handles it for you.
the big pros that i have actually seen though for having this be pluggable and not hard-coded (with the exception of the URL although you can do this dynamically as well) is what happens if you switch databases. if you import the package and use fully named classes and you switch databases at some point (could be just an upgrade of the same vendor's database) you are screwed.
same problem could happen if you switch drivers for some reason.
at any rate if you use things properly and are careful then you should only ever have to change your URL the rest of the code is fine if you use the DriverManager and use the drivers dynamically otherwise...

Why Class.forName?...

I'm trying to understand the use of Class.forName in JDBC programing. �What is the really goal for this class?
try{
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
} catch(ClassNotFoundException ex){
// something
Regards.

I'm trying to understand the use of Class.forName in
JDBC programing. �What is the really goal for this
class?There are two implied questions...
-What does it do?
1. The class is loaded. All classes are loaded this way but normally the compiler does the work for you.
2. When a class is loaded, if there are any 'static initializers' in the class then those are run. Again true for any class when it is loaded.
3. JDBC drivers have a static initializer which registers the driver with the JDBC driver manager. See the DriverManager.registerDriver(Driver driver) method and the JDBC spec for more specific info.
-Why it is done this way?
As a guess because the original JDBC implementor(s) just found out about static initializers and thought they were 'cool'. It would be just as easy and more meaningful to do it using a different methodology.

How does Class.forName() get a driver registered with DriverManager

From the documentation, Class.forName() tends to loads the specified class via the class loader. But if we use it to load the class of a jdbc connection driver, how does it get automatically registered with DriverManager?
Neerav

yorkroad wrote:
No. Class.ForName("whatever") intializes the class. As for registering it with the DriverManager, this is from the API:
When the method getConnection is called, the DriverManager will attempt to locate a suitable driver from amongst those loaded at initialization and those loaded explicitly using the same classloader as the current applet or application.
You could use DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver()); which does it all in one. (Although keep in mind that will require an Oracle import in your code!)
m
Edited by: yorkroad on Nov 4, 2009 3:42 PMNo, loading the Class with Class.forName already registers the driver, as already said. Where DriverManager "searches" is among those registered classes. The method detailed above does not do anything more than simply calling Class.forName() with the added drawback that the Driver jarfile must be present at compile time, and, in order to change DBs you would have to change and recompile your code.

Why use Class.forName() ?

Why is it always adviced to use Class.forName( nameOfTheDriver ). Why dont we simply import the driver via the import statement ?
Please note that this topic is part of a bigger topic I published in Java programming about difficulties I had importing driver. See:
http://forums.java.sun.com/thread.jsp?forum=31&thread=147534
for more details.

Because using an import statement only tells the compiler about the driver. Class.forName() actually loads the driver when the program runs, which is what you want to happen.

Unable to load Driver Class

Hi There:
When I try to connect to the Oracle 8i via this applet , I get the following run time error.
Any help will be appreciated.
I am using j2sdkee1.3.1, jdk1.3.1_02 and Oracle8.
I also need your suggestion please. I have inserted some BLOB data in the Oracle table. I will need to display the BLOB data to the end users. I plan to convert this BLOB data into string format so that my applet can display the same. Further the string will have to be edited by the end users. I will then convert this modified string back to byte array so that I can insert the same as BLOB.
Please let me know applet or the servlet? Which is better option.
Users are reluctant to use any kind of WebServer because it will introduce the additional layer of complexity.
Any help will be greatly appreciated.
Thanks in advance.
C:\>AppletViewer JdbcApplet.html
Unable to load Driver Class
java.lang.ClassNotFoundException: java.io.FileNotFoundException: C:\oracle\jdbc\
driver\OracleDriver.class (The system cannot find the path specified)
The following code snippet fails because it is unable to find the suitable driver.
if (conn == null)
     //make a connection to the db
     try {
          // conn = DriverManager.getConnection ("jdbc:oracle:thin:@"+"localhost:1521:sys", "system", "manager");
          // conn = DriverManager.getConnection ("jdbc:oracle:thin:system/manager@(description=(address_list= (address=(pro tocol=tcp)(host=localhost)(port=1521)))(source_route=yes)(connect_data=(sid=sys)))" );
          Class.forName("oracle.jdbc.driver.OracleDriver");
          String conurl="jdbc:oracle:thin:@localhost:1521:sys";
          Connection con=DriverManager.getConnection(conurl,"system","manager");
     } catch ( Exception e ) {
          System.out.println ("Unable to load Driver Class");
          e.printStackTrace (System.out);
          // add send email notification about this fact
          return false;
} // End of if Statement from conn...

Hi,
maybe I'm too late but try the following :
It seems that Your IDE doesn't check the path to Your classesxxx.zip file.
Or Your classesxxx.zip file is corrupt.
We had this error after downloading the classes12.zip for Oracle versions
higher 8.1.6.
The original size of this file is 1.888kB.
Remember Windows FTP is downloading in ascii mode per default.
Or Your classpath isn't correct
( the Exception souns like this )
Regards

Help Please .... Unable to load Driver Class

Hi There:
When I try to connect to the Oracle 8i via this applet , I get the following run time error.
Any help will be appreciated.
I am using j2sdkee1.3.1, jdk1.3.1_02 and Oracle8.
I also need your suggestion please. I have inserted some BLOB data in the Oracle table. I will need to display the BLOB data to the end users. I plan to convert this BLOB data into string format so that my applet can display the same. Further the string will have to be edited by the end users. I will then convert this modified string back to byte array so that I can insert the same as BLOB.
Please let me know applet or the servlet? Which is better option.
Users are reluctant to use any kind of WebServer because it will introduce the additional layer of complexity.
Any help will be greatly appreciated.
Thanks in advance.
C:\>AppletViewer JdbcApplet.html
Unable to load Driver Class
java.lang.ClassNotFoundException: java.io.FileNotFoundException: C:\oracle\jdbc\
driver\OracleDriver.class (The system cannot find the path specified)
The following code snippet fails because it is unable to find the suitable driver.
if (conn == null)
     //make a connection to the db
     try {
          // conn = DriverManager.getConnection ("jdbc:oracle:thin:@"+"localhost:1521:sys", "system", "manager");
          // conn = DriverManager.getConnection ("jdbc:oracle:thin:system/manager@(description=(address_list= (address=(pro tocol=tcp)(host=localhost)(port=1521)))(source_route=yes)(connect_data=(sid=sys)))" );
          Class.forName("oracle.jdbc.driver.OracleDriver");
          String conurl="jdbc:oracle:thin:@localhost:1521:sys";
          Connection con=DriverManager.getConnection(conurl,"system","manager");
     } catch ( Exception e ) {
          System.out.println ("Unable to load Driver Class");
          e.printStackTrace (System.out);
          // add send email notification about this fact
          return false;
} // End of if Statement from conn...

Hi,
maybe I'm too late but try the following :
It seems that Your IDE doesn't check the path to Your classesxxx.zip file.
Or Your classesxxx.zip file is corrupt.
We had this error after downloading the classes12.zip for Oracle versions
higher 8.1.6.
The original size of this file is 1.888kB.
Remember Windows FTP is downloading in ascii mode per default.
Or Your classpath isn't correct
( the Exception souns like this )
Regards

Class.forName(driver) = ClassNotFoundException

hy all!
the following statements causes an error:
Class.forName("oracle.jdbc.driver.OracleDriver");I printed some informations about the exception:
Errorcause: null
Errormessage: oracle.jdbc.driver.OracleDriver
Class: class java.lang.ClassNotFoundException
StackTrace: [Ljava.lang.StackTraceElement;@16
(I�m using JDeveloper)
what do I have to do?? Is something missing on my harddrive??
can you guide me?
thanks!
lenaz

oracle jdeveloper build 10.1.2
1. select the project then right click
2. select the project properties
3. expand the Profiles and select the libraries
4. select the Oracle JDBC then click >
5. click ok

Why is Class.forName( ) so useful?

I still don't get why Class.forName so useful to java?
If I do:
Class c = Class.forName("dog");
Dog d = c.newInstance();But what's wrong with:
Dog d = new Dog();Why does java need that Class.forName thing? Can anyone give an counter example to demonstrate the case in my second way won't work?
Thanks.

cpthk wrote:
I still don't get why Class.forName so useful to java?
If I do:
Class c = Class.forName("dog");
Dog d = c.newInstance();But what's wrong with:
Dog d = new Dog();Why does java need that Class.forName thing? Can anyone give an counter example to demonstrate the case in my second way won't work?
System.out.println("Class to instantiate?");
String className = scanner.nextLine();
Class c = Class.forName(className);
Object o = c.newInstance();Also, Class has a lot more methods besides just forName().

Contructors + class.forName()

Howdy.
I'm having a bit of a problem but I'm not sure why. I'm trying to load-up a postgreSQL database and can do it from within the main method of a small, self-contained program, but I can't once I place the call in a constructor instead.
public class DB
     public static void main(String[] argv)
          System.out.println("Checking if Driver is registered with DriverManager.");
          try
               Class.forName("org.postgresql.Driver");
          catch (ClassNotFoundException cnfe)
               System.out.println("Couldn't find the driver!");
               System.out.println("Let's print a stack trace, and exit.");
               cnfe.printStackTrace();
               System.exit(1);
...Works, no error shows up.
public class DataB
     public DataB()
          System.out.println("Checking if Driver is registered with DriverManager.");
          try
            Class.forName("org.postgresql.Driver");
          catch (ClassNotFoundException cnfe)
            System.out.println("Couldn't find the driver!");
            System.out.println("Let's print a stack trace, and exit.");
            cnfe.printStackTrace();
            System.exit(1);
                              ...Doesn't work.
When I make an instance of DataB, the error I get is "Java.Lang.ClassNotFoundException: org.postgresql.Driver".
It can't be where these two programs are, as they are both in the same package of a project and use the same imports. The program that creates the instance of DataB is in a different package (same project). It's a simple create
databasePackage.DataB Data = new databasePackage.DataB();Is there something obvious I'm overlooking?

Well, even when I change the original program (that works) from:
public class DB
     public static void main(String[] argv)
//     public DB()
          System.out.println("Checking if Driver is registered with DriverManager.");
          try
               Class.forName("org.postgresql.Driver");
          catch (ClassNotFoundException cnfe)
               System.out.println("Couldn't find the driver!");
               System.out.println("Let's print a stack trace, and exit.");
               cnfe.printStackTrace();
               System.exit(1);
...to
public class DB
//     public static void main(String[] argv)
     public DB()
          System.out.println("Checking if Driver is registered with DriverManager.");
          try
               Class.forName("org.postgresql.Driver");
          catch (ClassNotFoundException cnfe)
               System.out.println("Couldn't find the driver!");
               System.out.println("Let's print a stack trace, and exit.");
               cnfe.printStackTrace();
               System.exit(1);
...and try to create an instance, it stops working, same error.

ClassNotFoundException when using Class.forName(), thx

in a study app, i try to use Class.forName() to load any class then get its properties (fields, methods etc. vs reflect).
the (Frame based) app is in directory:
c:\app\StudyApp.class
there is a "Open class" button on the app, click the button, i use FileChooser to open any class file.
i.e. open a class (assume it is not packaged)
d:\dir\TheClass.class
coding in StudyApp.java is:
Class cls=Class.forName("TheClass");
now a ClassNotFoundException throws when call Class.forName() above.
it is easy to understand why throw the exception because i never tell where the class is. it is in directory
d:\dir
my question is: how to tell VM the directory.
the directory d:\dir can not be applied to -classpath when run java.exe StudyApp, because the directory is random one at run-time.
i tried to change System property (i.e. "java.class.path", 'user.dir" etc. none of them can fix the problem.
thanks in advance for any help

This probably does a lot more than you need:
import java.util.*;
import java.io.*;
import java.util.jar.*;
import java.lang.*;
public class ClassFileFinder extends ClassLoader
     List cpath = new LinkedList();
     void addFile(File f) {
          if(f.isDirectory() || (f.isFile() && f.canRead() &&
                                      f.getName().endsWith(".jar")))
               cpath.add(f);
     public byte[] classData(String className) {
          String cname = className.replace('.', File.separatorChar) + ".class";
          Iterator it = cpath.iterator();
          while(it.hasNext()) {
               File f = (File)it.next();
               try {
                    if(f.isDirectory()) {
                         File cFile = new File(f, cname);
                         if(cFile.isFile()) {
                              byte[] buf = new byte[(int)cFile.length()];
                              InputStream in = new FileInputStream(cFile);
                              int off = 0, l;
                              while((l = in.read(buf, off, buf.length - off)) > 0) {
                                   off += l;
                                   if(off >= buf.length) break;
                              in.read(buf);
                              in.close();
                              return buf;
                    } else if (f.isFile()) {
                         JarFile jar = new JarFile(f);
                         JarEntry ent = jar.getJarEntry(cname);
                         if(ent != null) {
                              byte[] buf = new byte[(int)ent.getSize()];
                              int off = 0, l;
                              InputStream in = jar.getInputStream(ent);
                              while((l = in.read(buf, off, buf.length - off)) > 0) {
                                   off += l;
                                   if(off >= buf.length) break;
                              in.close();
                              return buf;
               } catch (IOException e) {
          return null;
     public Class findClass(String className) throws ClassNotFoundException{
          byte[] data = classData(className);
          if(data == null)
               return getParent().loadClass(className);
          else
               return defineClass(className,data,0, data.length);
}Create an instance, Add directories and/or jar files with addFile then loadClass the class you want.

Class.forName() debunked

This issue is about: Dynamic loading and Inheritance.
Debugging an odd ClassNotFoundException in a J2EE Application, I was involved investigating deeply Class.ForName(). This method - namely the version with only the class name as parameter - is used inside xsdbeans.jar, an optiopnal library, shipped with IBM WebSphere 5.x. Moving the jar from the EAR classloader to the server runtime classloader caused weird behavior on my app.
I try to simplify the core question:
Suppose class E extends B. Base class B declares an instance method, dynLoad(String name) that uses internally Class.forName(String name).
Say 'e' an instance of E. Invoking e.dynLoad("Foo"), Class.forName("Foo") should use the ClassLoader of current class. But which is the 'current class': E or B? Is it the class of current object (E) or the declaring superclass (B)?
My instinctive answer was: E. But my J2EE app was behaving as the current class was B. Indeed E and B may be defined by different classloaders, and this makes a big difference.
A rapid lookup at Sun's docs confirmed my first hypothesis:
http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Class.html#forName(java.lang.String)
> Returns the Class object associated with the class or interface with the given string name.
Invoking this method is equivalent to:
Class.forName(className, true, currentLoader)
where currentLoader denotes the defining class loader of the current class.
ok, this is a little misleading, but going on:
http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Class.html#forName(java.lang.String,%20boolean,%20java.lang.ClassLoader)
> For example, in an instance method the expression:
>
Class.forName("Foo")
is equivalent to:
Class.forName("Foo", true, this.getClass().getClassLoader())
Not equivocal. The current class is the class of current object, no matter (apparently) if the instance method is declared in a superclass.
Right? Wrong. Here a minimal counter-example:
//-- B.java
import java.net.*;
public class B {
    public void dynLoad(String name) throws Exception {
        System.out.println(getClass().getSuperclass()
            + " defining classloader is: "
            + getClass().getSuperclass().getClassLoader());
        System.out.println(getClass()
            + " defining classloader is: "
            + getClass().getClassLoader());
        System.out.println("\n1) Class.forName(\""+name+"\");");
        // Loading with 'currentLoader'
        Class.forName(name)
            .newInstance();
        System.out.println("\n2) Class.forName(\""+name
            +"\", true, this.getClass().getClassLoader());");
        // This should be equivalent (by Sun J2SE API spec)
        Class.forName(name, true, this.getClass().getClassLoader())
            .newInstance();
    public static void main(String[] args) {
        ClassLoader syscl = ClassLoader.getSystemClassLoader();
        if (!URLClassLoader.class.isInstance(syscl)) {
            System.err.println("Cannot continue the trick.");
            System.exit(1);
        URL[] urls = ((URLClassLoader)syscl).getURLs();
        // Yet Another ClassLoader
        URLClassLoader yacl = new URLClassLoader(urls) {
            // Force Parent-last delegation policy to assure
            // demanded classes are defined by _this_ classloader
            public Class loadClass(String name)
                throws ClassNotFoundException {
                Class c = findLoadedClass(name);
                if (c == null) {
                    try {
                        // Simulate no visibility to base class to assure
                        // it is _not_ defined by this classloader too
                        if (name.equalsIgnoreCase("B")) {
                            throw new ClassNotFoundException();
                        c = findClass(name);
                    } catch (ClassNotFoundException e) {
                        c = getParent().loadClass(name);
                return c;
        try {
            // Loading class E with a different classloader
            Class c = yacl.loadClass("E");
            c.getMethod("dynLoad", new Class[]{String.class})
                .invoke(c.newInstance(), new Object[]{"Foo"});
        } catch (Exception ex) {
            ex.printStackTrace();
            System.exit(1);
//-- E.java
public class E extends B {
//-- Foo.java
public class Foo {
public Foo() {
    System.out.println(getClass()
      + " defining classloader is: "
      + getClass().getClassLoader());
}Running above B.main() produce the following output on Sun JDK 1.3, 1.4.2, 1.5:
> class B defining classloader is: sun.misc.Launcher$AppClassLoader@3d200480
class E defining classloader is: B$1@3d2c0480
1) Class.forName("Foo");
class Foo defining classloader is: sun.misc.Launcher$AppClassLoader@3d200480
2) Class.forName("Foo", true, this.getClass().getClassLoader());
class Foo defining classloader is: B$1@3d2c0480
The evidence is that classloader used is not the same. in the case 1) it uses the classloader of superclass B. Hence the two form of Class.forName() invocation are not equivalent, as stated in Sun documentation.
Disclosure
The evidence is confirmed and explained looking at Sun's implementation of java.lang.Class.java and java.lang.ClassLoader.java: finally the Class.forName(String name) relies on sun.reflect.Reflection.getCallerClass(int) to find the famous 'current class' mentioned in the javadocs. This undocumented method returns the i-th caller class of current stack frames; each stack frame represents a method invocation coupled with its declaring class.
I wonder why in Sun docs this poorly explained issue was remaining immutable from 1.3 to date. Furthermore: which was the intended behavior? Another reason to the long said "Class.forName() is evil..." or am I missing something?
regards, Lorenzo

Of course, it comes down to the question: What is the current class?
Not something well defined. You are looking for this.getClass(), it's taking the class at compile time. If it went your way, woundn't that create an inconsistency in forName in static vs instance contexts?
Actually I think the static approach is more natural, because it means that forName behaves the way that resolving external references work. Your way would also go against the spirit of Java security policies which requires references down the classloader chain something to be treated with suspision.
The mechanism intended, I think, for these situations is the contextClassLoader property of Thread. When executing plugin type code the contextClassLoader should be set to the ClassLoader that loaded the plugin, and any references to resources or dynamic class loads from the plugin should be made using the contextClassLoader. This enables your shared library code to access classes and resources on behalf of the plugin code with access to classes and resources inside the plugin.
Thus, if you write library code or other container stuff likely to be called from a plugin you should probably always use:
Class cls = Thread.currentThread().getContextClassLoader().loadClass("foo");

Ojdbc14 can't load driver

Hi,
I built an application using among others the ojdbc14.jar - working "perfectly" in eclipse.
But when I create a jar - I receive an "Class-not-found-Exception", when the
Class.forName("oracle.jdbc.driver.OracleDriver"); is invoked.
I tried using newInstance() but it didn't work.
The classpath seems to be correct:
<?xml version="1.0" encoding="UTF-8"?>
<classpath>
     <classpathentry kind="src" path=""/>
     <classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER"/>
     <classpathentry kind="lib" path="ojdbc14.jar"/>
     <classpathentry kind="output" path=""/>
</classpath>I also "included" the jar(s) in the manifest:
Bundle-ClassPath: ojdbc14.jarwhen I use instead of the "...getName()..."
DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());I don' receive the ClassNotFoundError"- but the jar doesn't do anything (seems like hanging-up)
Of cause they are included in the jar. ;)
So - where is the bug? Do I have to use another command than the
forName to load the driver?
Thanks for any tip.
adicko

DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver());
String jdbcURL="jdbc:oracle:thin:@"
+"192.168.0.96"//jdbcHost
+":1521"//port
+":db12"//service name
//Another format: DriverManager.getConnection("jdbc:oracle:oci8:@","user", "passwd");
should work normally. If not, try to download a JDBC packag from Oracle site.

Why class.forName to load driver

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