What is Class.forName

We are using Class.forName("driver class") statement for registering the driver class. But after writing this statement we are not using any refernce to that Class.forName, why it is needed actually.

It causes the class to get loaded. That in turn causes the static initializer to run. Which registers it as an available driver, allowing you to use it from within JDBC.

Similar Messages

What to do with Class.forName(), Class.getName() when Obfuscating

hi,
I have been asked at my company to perform Obfuscation of our project-code, The problem I have been facing is,
We have got too many Class.forName(), Class.getName() calls in our Project-code, which is really hindering the process of Obfuscating all the Classes (refrences in code may break for all these classes which are dynamically being asked for, hence the project may suffer). And it is a pain-in-neck to really resolve which classes to exclude so that code should not break after obfuscation.
What my question is:
Do we have some automated tool to take care of all these Reflection API calls, so that work left to us is minimal?
If not, Do we have some short-cut (program, tool etc.) to identify all the classes which should be excluded?

Which program are you using when obfuscating?
In RetroGuard you can for example avoid certain class names, or packages, to be obfuscated.

What is the Difference between ? new Operator and Class.forName() ???

plz tel me ....
what is the Difference between ? new Operator and Class.forName() ??? ........

Class.forName(), takes the class name as parameter,
and loads that class in memory. But it doesn't create
any instance of that class.
That means static methods/variables are available for
use.
new keyword, checks if the class is loaded, if not
then loads that class, and then creates an instance
of that class.Class.forName actually returns the class object for that name (class - for -name). it might load it, if the class hasn't already been loaded, but it's misleading to say that's what that method does
your definition of 'new' is wrong, too. give the dukes back

What is actually do class.forname

hi
experts
what is actually mean when we write
class.forName("sun.jdbc.odbc.....")
what actually does class.forName
plz give me a code to connect with mysql database on linux.

no, it doesn't. will people please please please
stop telling other people this. it's
completely wrong.It is?
Then why does the API documentation claim that "a
call to forName("X") causes the class named X to be
initialized?"
http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Clas
s.html#forName%28java.lang.String%29because I misread "initialized" for "instantiated" in the above post! sorry! usually when this question comes up, the stock answer is "it instantiates the class"
my mistake

Class.forName, how to use it in the case?

we have a java application:
c:\app\TestForName.class
inside the app, there is a call:
Class.forName("ClassLib");
ClassLib.class is a simplest class for testing with no package.
ClassLib.class can be in any directory except the app's directory
c:\app
because ClassLib.class stands for our library class for multiple projects and multiple uses, it is not allowed to be in a special app directory.
and, ClassLoader and URLClassLoder are not suitable in our case.
i tried following 3 ideas, none of them is OK, please help.
1. put ClassLib.class in directory
c:\lib\
(that is c:\lib\ClassLib.class)
call application with command -cp
java -cp c:\lib;....; TestForName
(method Class.forName("ClassLib") call is inside TestForName.class)
2. put ClassLib.class in
c:\jdk\bin\
(VM says it is one of "java.library.path")
java -cp ....; TestForName
3. put ClassLib.class in
c:\jdk\JAR\classes\
(VM says if is one of "sun.boot.class.path")
java -cp ....; TestForName
i really wondering how to make Class.forName() call successfuf inside application TestForName.class
1. which directory is right place for ClassLib.class
2. how to change command line or java code inside TestForName.class
thx for any help.

Why don't u use a class loader. Try this code
// loader class
public class Loader extends ClassLoader {
    String path;
    public Loader(String path) {
          this.path = path;
    public Class findClass(String name) {
        byte[] b = loadClassData(path+name+".class");
        return defineClass(name, b, 0, b.length);
    private byte[] loadClassData(String name) {
        File file = new File(name);
        byte[] data = null;
        try {
            InputStream in = new FileInputStream(file);
            data = new byte[ (int) file.length()];
            for (int i = 0; i < data.length; i++) {
                data[i] = (byte) in.read();
        catch (IOException ex) {
        file = null;
        return data;
// in your caller class use
   Loader loader = new Loader(libPath); // lib path may be taken from a command line arg
   Object main = loader.loadClass("ClassLib", true).newInstance();I think this is what u r looking for
Uditha Nagahawatta

Error in Class.forName("com.mysql.jdbc.driver")

Hi forum,
Please help me to solve the issue.
im using the following jsp code for genrating the reports using JASPER REPORTS
the JSP FILE
<%@ page contentType="text/html;charset=windows-1252"%>
<%@ page import="java.io.*"%>
<%@ page import="java.util.*"%>
<%@ page import="java.sql.*"%>
<%@ page import="javax.sql.DataSource"%>
<%@ page import="javax.naming.InitialContext"%>
<%@ page import="net.sf.jasperreports.engine.*"%>
<%@ page import="net.sf.jasperreports.engine.design.JasperDesign"%>
<%@ page import="net.sf.jasperreports.engine.xml.JRXmlLoader"%>
<%@ page import="net.sf.jasperreports.engine.export.*" %>
<%@ page import ="net.sf.jasperreports.engine.*"%>
<%@ page import ="net.sf.jasperreports.engine.JasperFillManager"%>
<%@ page import ="net.sf.jasperreports.engine.JRException"%>
<%@ page import="net.sf.jasperreports.engine.JasperReport"%>
<%@ page import="net.sf.jasperreports.engine.JasperPrint"%>
<html>
<body bgcolor="00ffcc">
<%
try{
Connection con = null;
String url="jdbc:mysql://localhost/customer";
String username = "root";
String password = "cmsadmin";
InputStream input=new FileInputStream(new File("C:/Documents and Settings/user/My Documents/NetBeansProjects/jasperreports/web/helloworld.xml"));
JasperDesign design = JRXmlLoader.load(input);
JasperReport report = JasperCompileManager.compileReport(design);
Map params = new HashMap();
params.put("reportTitle", "helloworld");
params.put("author", "Muthu Kumar");
params.put("startDate", (new java.util.Date()).toString());
params.put("ReportTitle", "PDF JasperReport");
<img class="emoticon" src="images/emoticons/confused.gif" border="0" alt="" />Class.forName("com.mysql.jdbc.Driver");<img class="emoticon" src="images/emoticons/confused.gif" border="0" alt="" /><img src="images/emoticons/confused.gif" border="0" alt="" />
con = DriverManager.getConnection(url,username,password);
JasperPrint print = JasperFillManager.fillReport(report, params, con);
OutputStream output=new FileOutputStream(new File("C:/Documents and Settings/user/My Documents/NetBeansProjects/jasperreports/helloreportworld.pdf"));
JasperExportManager.exportReportToPdfStream(print, output);
// JasperViewer.viewReport(print);
catch(SQLException es) {
out.println(es);
catch(JRException ex){
//ex.printStackTrace();
out.println(ex);
%>
</body>
</html>The error it is saying is in the line Class.forName(....) ;
Please look for the emoctions with question mark
i DOn know what to do.
Please help
Im comparin the below JRXML file as with the above code
<?xml version="1.0"?>
<!DOCTYPE jasperReport
PUBLIC "-//JasperReports//DTD Report Design//EN"
"http://jasperreports.sourceforge.net/dtds/jasperreport.dtd">
<jasperReport name="helloworld">
<parameter name="reportTitle" class="java.lang.String"/>
<parameter name="author" class="java.lang.String"/>
<parameter name="startDate" class="java.lang.String"/>
<queryString>
<![CDATA[SELECT * FROM customer order by UserID ]]>
</queryString>
<field name="UserID" class="java.lang.String"/>
<field name="UserName" class="java.lang.String"/>
<field name="City" class="java.lang.String"/>
<field name="State" class="java.lang.String"/>
<title>
<band height="60">
<textField>
<reportElement x="0" y="10" width="500" height="40"/>
<textElement textAlignment="Center">
<font size="24"/>
</textElement>
<textFieldExpression class="java.lang.String">
<![CDATA[$P{reportTitle}]]>
</textFieldExpression>
</textField>
<textField>
<reportElement x="0" y="40" width="500" height="20"/>
<textElement textAlignment="Center"/>
<textFieldExpression class="java.lang.String">
<![CDATA["Run by: " + $P{author}
+ " on " + $P{startDate}]]>
</textFieldExpression>
</textField>
</band>
</title>
<columnHeader>
<band height="30">
<rectangle>
<reportElement x="0" y="0" width="500" height="25"/>
<graphicElement/>
</rectangle>
<staticText>
<reportElement x="5" y="5" width="50" height="15"/>
<textElement/>
<text><![CDATA[UserID]]></text>
</staticText>
<staticText>
<reportElement x="55" y="5" width="150" height="15"/>
<text><![CDATA[UserName]]></text>
</staticText>
<staticText>
<reportElement x="205" y="5" width="255" height="15"/>
<text><![CDATA[City, State]]></text>
</staticText>
</band>
</columnHeader>
<detail>
<band height="20">
<textField>
<reportElement x="5" y="0" width="50" height="15"/>
<textElement/>
<textFieldExpression class="java.lang.String">
<![CDATA[$F{UserID}]]>
</textFieldExpression>
</textField>
<textField>
<reportElement x="55" y="0" width="150" height="15"/>
<textElement/>
<textFieldExpression class="java.lang.String">
<![CDATA[$F{UserName}]]>
</textFieldExpression>
</textField>
<textField>
<reportElement x="205" y="0" width="255" height="15"/>
<textElement/>
<textFieldExpression class="java.lang.String">
<![CDATA[$F{City} + ", " + $F{State}]]>
</textFieldExpression>
</textField>
</band>
</detail>
</jasperReport>

Glass_Fish wrote:
I have set the classpath in the environment variables in the my computer properties.The web container has it's own properties. The "system" classpath means absolutely nothing to it. Read your server's documentation.

Class.forName() with dynamic String

I'm trying to create objects of a class whose name depends on a runtime database lookup. So my code looks like this:
package com.mycompany.ourproduct.ourpackage;
String className = rs.getString(1);
Class c = Class.forName(className);
When I run the program, I get a ClassNotFoundException. But everything runs fine if I replace the code above with this:
package com.mycompany.ourproduct.ourpackage;
// String className = rs.getString(1);
String className = "com.mycompany.ourproduct.ourpackage.oursubpackage.MyClass"
Class c = Class.forName(className);
The problem seems to be in the dynamic linking. Although the class I'm trying to load is in a different package, it is a public class (and I can load it with a static string). Neither does moving it to the same package fix the problem.
I've noticed that if I supply a mis-named class with a static string, the exception reads:
java.lang.ClassNotFoundException: com.mycompany.ourproduct.misspelledpackage.SomeClass
but the same exception prints as follows when the string comes from the database:
java.lang.ClassNotFoundException: com/mycompany/ourproduct/misspelledpackage/SomeClass
I thought the difference was one of compile-time linking and run-time linking, but oddly enough, I still get the dots for misspelled classes that I (1) supply on the command line, (2) read from a file, or (3) concatenate from command line arguments plus info from a file. It's just when I pull the class name from the database that I get the slashes. Does anyone know what's going on?
Here's what I get from java -version:
java version "1.2.2"
Solaris VM (build Solaris_JDK_1.2.2_05a, native threads, sunwjit)
Any help would be greatly appreicated!

Hmm. Weird. Have you looked at the String you're getting back from the database? Does it have slashes or dots? (Should be dots.) Have you made sure any leading/trailing spaces have been trimmed? Try doing classname.equals("com.mycompany... etc.") to see if it really is the same string as the constant that does work.
If it turns out the String is correct, and the only difference is whether that String came from a databaes or a literal, then I don't know what's going on. The first step, though, is to verify whether that's really the case, or if you're not getting the String you think you are.

Class.forname("").newInstance(); = Problem!! ;)

I am distributing the application I am developping as a Jar file...
In my application, there is a tool which interacts with a Database..
As there is more than 1 existing database, and that they all require different drivers, I do not want to have to put every driver into my jar file, since it makes the file too big... I'd like to make it possible to download the drivers separatly, as another jar file... Although when I do that, I am not able to create a new instance of the driver...
Here's what I have:
Class.forName("org.gjt.mm.mysql.Driver").newInstance();
This works fine when the driver has been included in the same jar file as my program.. How could I get it to work if the driver is in a separate Jar file, in the same folder as the jar file of my own application?

I am distributing the application I am developping as
a Jar file...
In my application, there is a tool which interacts
with a Database..
As there is more than 1 existing database, and that
they all require different drivers, I do not want to
have to put every driver into my jar file, since it
makes the file too big... I'd like to make it
possible to download the drivers separatly, as another
jar file... Although when I do that, I am not able to
create a new instance of the driver...
Here's what I have:
Class.forName("org.gjt.mm.mysql.Driver").newInstance();
This works fine when the driver has been included in
the same jar file as my program.. How could I get it
to work if the driver is in a separate Jar file, in
the same folder as the jar file of my own application?I think the problem may be the classpath since it has to include the jar name specifically to find the classes in them. Perhaps you can set a new classpath with the System.setProperties() function so that the Class.forName() will work. I haven't tried that so I don't know if it will work.

Class.forname (help please)

Hello,
I would like to load a class with class.forname. BUT, I just know the package and the path to the class. This class its not on class-path...
What I know is:
class: myClass
package: org.java
location: c:\myClases
current class path: c:\myClassPath
Class.forName("org.java.myClass");
this above does not works because org.java.myClass its not on classpath
Any ideas?

URL directory = new URL("file:/location where your package is/"); // dont forget to end it with /
URL[] classPath = new URL[] {directory};
ClassLoader loader = URLClassLoader.newInstance(classPath);
Class youClass = Class.forName("org.java.myClass", true, loader);

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.

How to create an object of our own class by using Class.forName()??

how to create an object of our own class by using Class.forName()??
plzz anser my qustion soon..

Class.forName does not create an object. It returns a reference to the Class object that describes the metadata for the class in question--what methods and fields it has, etc.
To create an object--regardless of whether it's your class or some other class--you could call newInstance on the Class object returned from Class.forName, BUT only if that class has a no-arg constructor that you want to call.
Class<MyClass> clazz = Class.forName("com.mycompany.MyClass");
MyClass mine = clazz.newInstance();If you want to use a constructor that takes parameters, you'll have to use java.lang.reflect.Constructor.
Google for java reflection tutorial for more details.
BUT reflection is often abused, and often employe when not needed. Why is it that you think you need this?

Strange use of Class.forName() in JDBC

The following is the classical code to retreive data from a database via JDBC
        Connection con;
        Statement stmt;
        String querystring;
        String parametervalue = "";
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch(java.lang.ClassNotFoundException e) {
            System.err.print("ClassNotFoundException: ");
            System.err.println(e.getMessage());
        try {
            con = DriverManager.getConnection(dburl);
            stmt = con.createStatement();
            querystring = "select ParameterValue from Profile ";
            ResultSet rs = stmt.executeQuery(querystring);
            if(rs.next()) parametervalue = rs.getString("ParameterValue");
            rs.close();
            stmt.close();
            con.close();
        } catch(SQLException ex) {
            System.err.println("-----SQLException-----");
            System.err.println("SQLState: " + ex.getSQLState());
            System.err.println("Message: " + ex.getMessage());
            System.err.println("Vendor: " + ex.getErrorCode());
        return parametervalue;         but the use of Class.forName("com.mysql.jdbc.Driver") is strange. it doesn't need to get the returned Class
like: Class t = Class.forName("com.mysql.jdbc.Driver"),and the DriverManager knows which driver to use!
Any one can give an explanation?
thanks

* It's more natural from an OO perspective for me to
tell the manager about the classes it manages thanfor
the classes to know about the manager and tell it
about themselves.
No.Hmmm. Care to elaborate? I don't have anything to really back this up, but it seems to me that a class shouldn't have to know too much about the context in which it is used. Drivers shouldn't have to know that there is a DriverManager that will be managing them. IMHO.
I thought of another reason: Since you're doing either the Class.forName or the DriverManger.register in the client, no work is saved there either way (as you said, register is just as easy to call as forName), but using Class.forName adds extra complexity in the Drivers. I guess this is probably the same as, or very close to "protected users from themselves" though.
If the forName() doesn't happen somewhere then the
class doesn't get loaded.I'm thinking more along the lines of classes getting loaded in a different area of the code than the DB client. Some kind of plugin-type thing maybe, where the plugin manager automatically loads all the classes in a certain classpath-like set of diretories and jars, without knowing or caring what each one is (DB plugin, graphics plugin, encryption plugin, messaging plugin, etc.) or how it's used. The DB client then wouldn't know which specific driver(s) it has available, only that whatever was visible to the plugin manager will be loaded, and some subset of that could be DB drivers.
In this situation, it's not appropriate for the plugin manager to register the drivers, since it doesn't know anything about JDBC, and it's not appropriate for the DB client to register them, since it doesn't know what classes the plugin manager loaded.
I suppose the DB client could query the plugin manager for all its loaded plugins, then check if each one implements Driver, and if it does, then register it. Or maybe the plugin manager could even store a map whose keys are interface Class objects or interface names and whose values are lists of the plugins that implement that interface.
I don't know if this scenario is used, or is even good design, but it doesn't seem too farfetched. This is the kind of situation where it seems to me the driver is the one in the best position to know both a) he has been loaded and b) he needs to be registered.

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

Diffrence between Class.forName() and new Operator

What is diffrence between class.forName() and new operator.Please tell in much detail.
Also about classloader.loadclass.
Suppose the class that we are tring to load with the help of class.forname is not compiled. Again if I make changes at runtime to that class will that get reflected.

What is diffrence between class.forName() and new
operator.Please tell in much detail.Class.forName loads a class. The new operator creates a new instance. Apple trees and apples.
Also about classloader.loadclass.Read the API.
Suppose the class that we are tring to load with the
help of class.forname is not compiled.Then you can't load it and get an exception. Read the API.
Again if I
make changes at runtime to that class will that get
reflected.Depends on the changes and when exactly you do them.

How to use class.forName

I am trying to use Class.forName() from a string which is passed to me as argument.
Class batchClass = Class.forName(args[1]);
A jar file contains the class file for the string received above and I have this jar file in the manifest of my executable jar.
I get a class not found exception when I run my executable jar
Can some body give pointers..what could possibly be the issue.
The jar file is in my classpath
run script
#!/bin/csh
java -jar -DDBPROVIDER=NO -DDBUS_ROOT=$DBUS_ROOT -DVTNAME=$VTNAME ./jar/IntraDayDepotPositionBatch.jar MagellanStart IntraDayDepotPositionBatch INPUTFILE LOGFILE
Exception
Magellan program starting - program class IntraDayDepotPositionBatch
Cannot find program class - IntraDayDepotPositionBatch
IntraDayDepotPositionBatch
java.lang.ClassNotFoundException: IntraDayDepotPositionBatch
at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:268)
at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:164)
at com.db.mmrepo.app.IntraDayDepotPositionBatch.MagellanStart.main(Unknown Source)
Thanks for your time and feedback on this

actually i tried both...with package name and without package name..
nothing worked...
my manifest file also contains the path to the package..so does the classpath

What is Class.forName

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