Saturday, September 06, 2008

Common Struts Errors and Causes

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This page contains errors and exceptions commonly encountered during web application development using Struts. Along with the exception or error messages themselves, potential causes of these errors are often listed along with links to additional resources.

I found this post here  and i think it will solve many problems you got when you were creating Struts Application.

To find the error you're looking for, use your browser's Find or Search capability and input a few words that you are seeing in your error message.

Cannot retrieve mapping for action
Exception: javax.servlet.jsp.JspException: Cannot retrieve mapping for action /Login
Probable Cause: No action defined in struts-config.xml to match that specified in the JSP's <html:form action="".

Cannot retrieve definition for form bean null
Exception: org.apache.jasper.JasperException: Cannot retrieve definition for form bean null
Probable Cause: This exception typically occurs because Struts cannot find the form bean it expects for a specific action according to the mapping in the struts-config.xml file. Most often, this is probably because the name given to the form in the name attribute of the form-bean element does not match the name attribute of the associated action's action element. In other words, the action and form should each have a name attribute that matches exactly, including case. It has been reported that this error has been seen when no name attribute is associated with the action. If there is no name attribute in an action element, no form is associated with the action. Others have reported this error as merely a symptom of something completely unrelated (all too common), but the mismatch of name attributes in the form-bean and action elements in the struts-config.xml file is the usual culprit.

Must specify type attribute if name is specified
Exception: Must specify type attribute if name is specified
Probable Cause:
This error is seen in conjunction with the Struts' HTML FORM tag. As the error message points out, the "name" attribute was used in the Struts HTML FORM tag (<html:form>), but the "type" attribute was not specified for this HTML FORM custom tag.

There are two easy ways to get around this:
  1. Remove name attribute altogether and specify only an action attribute, allowing Struts to figure out the form class from the struts-config.xml file.
  2. If you really want to use the name attribute, then specify the type attribute. This attribute should be set to the fully qualified (full package) class name of the class that is to be used as the ActionForm associated with the action. For example, the class attribute might be specified in the Struts HTML FORM tag as follows:

    <html:form action=""  name="MyFormBean"
Related Links: Struts FAQ / View / HTML

No action instance for path /xxxx could be created
Exception: No action instance for path /xxxx could be created
Probable Causes:
Special Note: Because so many different things can cause this error, it is recommended that you turn your error logging/debugging levels on your web server to a high level of verbosity to see the underlying problems in trying to instantiate the action class you have written and associated with the specified action xxxx through an action mapping in the struts-config.xml file.
Your Action class specified in the struts-config.xml file under the class attribute of the action mapping for action xxxx cannot be found for a variety of reasons, including (but not limited to):
  • Failure to place compiled .class file for the action in the classpath (needs to be under WEB-INF/classes with the appropriate directory structure underneath this that matches the package your Action class belongs to).
  • Package spelling or hierarchy specified in your action class itself (using the package keyword) does not match the spelling or complete package hierachy specified for your action class in the class attribute of the action in struts-config.xml. 
Action class specified in the /xxxx action mapping in the struts-config.xml file (class attribute) does not extend (directly or indirectly) from the Action class. In other words, your custom Action class does not extend off the Struts-provided Action class or off of another class that eventually extends the Action class (such as DispatchAction.
Problem in your classpath, such as web server not being able to find files in the WEB-INF/classes/ directory or specified subdirectory.
Problem in struts-config.xml file with action mapping.
Problem with data-sources.xml file.
Related Links:

Cannot find bean under name ...
Exception: Cannot find bean under name ...
Probable Cause: This is usually seen in association with a problematic Struts HTML SELECT custom tag. The Struts html:select tag behaves differently depending whether one or both of the name and property attributes is specified for its encompassed tags. If the name attribute is specified, whether or not if the property attribute is specified, then a bean matching the specified name will be expected in some scope (such as page, request, session, or application). If the matching bean is not found in any available scope, the error above will be seen.
There are two ways to address this. The first approach is to put a bean in one of the scopes so that the html:options might be associated with it. The second approach is to not specify the name attribute and instead use only the property attribute.

No getter method for property XXXX of bean org.apache.struts.taglib.html.BEAN
Exception: javax.servlet.jsp.JspException: No getter method for property username of bean org.apache.struts.taglib.html.BEAN
Probable Causes:
No getXXXX() method defined for form field with name XXXX.
This can happen if the JSP/Struts developer forgets that the name of the get method will have the same spelling as the value supplied in the Struts tag's property attribute, but that case will be different and is based on JavaBean specification rules. For example, my form class should have a getUsername method if my Struts form-related tag has username as the value for its property attribute. Note the difference in case marked with emphasis on the letter "U."
Related Links:
Case can trip up the matching between get method's name and name specified in Struts tag

java.lang.NoClassDefFoundError: org/apache/struts/action/ActionForm
Exception: java.lang.NoClassDefFoundError: org/apache/struts/action/ActionForm
Probable Causes:
This error occurs typically when the specified Java .class file cannot be located in the classpath. If this occurs at runtime of a web application (error shows on browser rather than a rendered page), this typically means that specified class is not in the web server's classpath (made up primarily of /WEB-INF/classes and /WEB-INF/lib contents). Note that the NoClassDefFoundError in general typically indicates lack of the specified class in the relevant classpath. In this particular case the missing class would be ActionForm.class
This error is sometimes seen when one or more ActionForm.class instances are actually in the classpath. This most often occurs when ActionForm.class is made available correctly by placing struts.jar in the /WEB-INF/lib directory. When this library has been correctly placed and it is verified that ActionForm.class actually is present in the struts.jar file, the problem is either that more than one copy of ActionForm.class is in the classpath or (more likely) that duplicate versions of class files other than ActionForm are in the same classpath, causing confusion. This is especially true if a class that extends ActionForm is made available twice, such as in an .ear file that encompasses a .war file as well as in the .war file's own classpath (/WEB-INF/classes). This problem can be resolved by guaranteeing that there are no redundant classes, especially those related to Struts (directly from Struts or extensions of Struts), in the web application's view.
Related Links:

Exception creating bean of class org.apache.struts.action.ActionForm: {1}
Exception: javax.servlet.jsp.JspException: Exception creating bean of class org.apache.struts.action.ActionForm: {1}
Probable Causes:
Instantiating Struts-provided ActionForm class directly instead of instantiating a class derived off ActionForm. This might occur implicitly if you specify that a form-bean is this Struts ActionForm class rather than specifying a child of this class for the form-bean.
Not associating an ActionForm-descended class with an action can also lead to this error.

Cannot find ActionMappings or ActionFormBeans collection
Exception: javax.servlet.jsp.JspException: Cannot find ActionMappings or ActionFormBeans collection
Probable Causes:
Either the <servlet> tags for the Struts action servlet or the        <servlet-mapping> tags for the .do extension mapping        or both not present in the web.xml file.  I saw a case        where the web.xml file had no elements other than the root element        and so this error was occurring.
Typos or spelling errors in the struts-config.xml can lead to this error message. For example, missing a slash ("/") on a closing tag can have this effect.
Another element that must be present in the web.xml file is the load-on-startup element. This can be either an empty tag or can have an integer specified that indicates the priority of executing the associated servlet. The higher the number in the load-on-startup tags, the lower its priority.
Another possibility, related to need to use load-on-startup tag, is that precompiling JSPs using Struts can lead to this message as well.
Related Links: 
Explicitly Define <load-on-startup>

NullPointerException at ... RequestUtils.forwardURL
Exception: java.lang.NullPointerException at org.apache.struts.util.RequestUtils.forwardURL(
Probable Causes: Missing path attribute in the forward subelement of the action element in struts-config.xml

Cannot find bean org.apache.struts.taglib.html.BEAN in any scope
Exception: javax.servlet.jsp.JspException: Cannot find bean org.apache.struts.taglib.html.BEAN in any scope.
Probable Causes: 
Trying to use Struts form subelement tags outside of the Struts' form tag. Note that this might be because you are using the Struts html tags after the closing tag.
Note that if you accidentaly make your opening html:form tag a no-body tag (you put a closing / at the end so that it looks something like ), this may be treated by your web server's parser as a no-body tag and everything after that tag you meant to be an opening tag will be outside of the form tag by default.
Note your prefix may be different than html, but most people seem to use that as their prefix for the Struts HTML tags library.

Related Links:
Using form subelements outside of a form tag 

Missing message for key xx.xx.xx
Exception: javax.servlet.jsp.JspException: Missing message for key xx.xx.xx
Probable Causes:
The key-value pair with specified key is not in file. file not in classpath (not in WEB-INF/classes directory in specified location)

Cannot find message resources under key org.apache.struts.action.MESSAGE
Exception: Cannot find message resources under key org.apache.struts.action.MESSAGE
Probable Causes:
Explicitly trying to use message resources that are not available (such as not available.
Implicitly trying to use message resources that are not available (such as using empty html:options tag instead of specifying the options in its body -- this assumes options are specified in file).
XML parser issues -- too many, too few, incorrect/incompatible versions.
Related Links:

No input attribute for mapping path /loginAction
Exception: No input attribute for mapping path /xxxxAction
Probable Causes: No input attribute in action mapping in struts-config.xml file for the action with the name specified in the error message. An input attribute is not required if form validation is not performed (either because the validate attribute is set to false or because the validation method in the relevant form class is not implemented. The input attribute specifies the page leading to this action because that page is used to display error messages from the form validation.

Strange Output Characters
Exception: Strange and seemingly random characters in HTML and on screen, but not in original JSP or servlet.
Probable Causes: 
Regular HTML form tags intermixed incorrectly with Struts html:form tags.
Encoding style used does not support characters used in page.

"Document contained no data" or no data rendered on page
"Document contained no data" in Netscape
No data rendered (completely empty) page in Microsoft Internet Explorer
Probable Cause: Employing a descendent of the Action class that does not implement the perform() method while using the Struts 1.0 libraries. Struts 1.1 Action child classes started using execute() rather than perform(), but is backwards compatible and supports the perform() method. However, if you write an Action-descended class for Struts 1.1 with an execute() method and try to run it in Struts 1.0, you will get this "Document contained no data" error message in Netscape or a completely empty (no HTML whatsoever) page rendered in Microsoft Internet Explorer.

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