JasperException: The value for the useBean class attribute is invalid

Question

org.apache.jasper.JasperException: /index.jsp(1,1) The value for the useBean class attribute com.b5 is invalid.
    org.apache.jasper.compiler.DefaultErrorHandler.jspError(DefaultErrorHandler.java:40)
    org.apache.jasper.compiler.ErrorDispatcher.dispatch(ErrorDispatcher.java:407)
    org.apache.jasper.compiler.ErrorDispatcher.jspError(ErrorDispatcher.java:148)
    org.apache.jasper.compiler.Generator$GenerateVisitor.visit(Generator.java:1272)
    org.apache.jasper.compiler.Node$UseBean.accept(Node.java:1178)
    org.apache.jasper.compiler.Node$Nodes.visit(Node.java:2361)
    org.apache.jasper.compiler.Node$Visitor.visitBody(Node.java:2411)
    org.apache.jasper.compiler.Node$Visitor.visit(Node.java:2417)
    org.apache.jasper.compiler.Node$Root.accept(Node.java:495)
    org.apache.jasper.compiler.Node$Nodes.visit(Node.java:2361)
    org.apache.jasper.compiler.Generator.generate(Generator.java:3426)
    org.apache.jasper.compiler.Compiler.generateJava(Compiler.java:216)
    org.apache.jasper.compiler.Compiler.compile(Compiler.java:332)
    org.apache.jasper.compiler.Compiler.compile(Compiler.java:312)
    org.apache.jasper.compiler.Compiler.compile(Compiler.java:299)
    org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:586)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:317)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

Can anyone explain the cause and solution of this problem?

Answer 1

Try type instead of class

The difference as per the documentation:

class="package.class" type="package.class" Instantiates a bean from the class named in class and assigns the bean the data type you specify in type. The value of type can be the same as class, a superclass of class, or an interface implemented by class. The class you specify in class must not be abstract and must have a public, no-argument constructor. The package and class names you use with both class and type are case sensitive. beanName="{package.class | }" type="package.class" Instantiates a bean from a class, a serialized template, or an expression that evaluates to a class or serialized template. When you use beanName, the bean is instantiated by the java.beans.Beans.instantiate method. The Beans.instantiate method checks whether the package and class you specify represents a class or a serialized template. If they represent a serialized template, Beans.instantiate reads the serialized form (which has a name like package.class.ser) using a class loader. The value of type can be the same as beanName, a superclass of beanName, or an interface implemented by beanName. The package and class names you use with both beanName and type are case sensitive.

Answer 2

The value for the useBean class attribute com.b5 is invalid.

So you have a

<jsp:useBean id="b5" class="com.b5" />

This exception is typical when the following happening "behind the scenes" fails:

com.b5 b5 = new com.b5();

Apart from the requirement that it should be placed inside a package (which you thus correctly did), the bean should itself be a public class and have an (implicit) public no-arg constructor. I.e.

package com;

public class b5 {

    public b5() {
        // Default constructor is optional when there are no other constructors.
    }
}

Normally this constructor is already present, but this will be hidden whenever you add other constructors which take other arguments. You'll then need to add it yourself explicitly.

package com;

public class b5 {

    public b5(String argument) {
        // Non-default constructor.
    }

    public b5() {
        // You need to explicitly add a default constructor.
    }
}

Another possible cause is that the bean class cannot be found in the runtime classpath. If this is your own bean, then ensure that its class file is located in /WEB-INF/classes/com/b5.class. Also ensure that the full qualified name com.b5 is literally correct, it's case sensitive. You should then look a bit further in the stacktrace for the exact cause of the problem. Head to the root cause or caused by parts at the bottom of the trace.

---

That said (and unrelated to the actual problem), the classname b5 is a pretty poor choice. It should be a sensible name starting with uppercase, e.g. User, Product, Order, etc. Also, using <jsp:useBean> instead of a servlet-based controller is a poor practice. If you're new to servlets, start at out servlets wiki page.