Question

I have a fileDownload component inside a dataTable but when I click it it seems the filedownloader is called before the datlis.filepath variable is set by setPropertyActionListener.

When I click download I get “Cant instantiate class: ui.FileDownloader.com.sun.faces.mgbean.ManagedBeanCreationException: Cant instantiate class: ui.FileDownloader.”

My jsf code is:

<p:column headerText="Metadata" style="width:40px">  
   <p:commandButton id="selectButton" rendered="#{datlis.has_metadata}" icon="ui-icon-circle-arrow-s" title="View" ajax="false" >  
      <f:setPropertyActionListener value="#{datlis.filepath}" target="#{filedownloader.filepath}" />  
      <p:fileDownload value="#{filedownloader.file}" /> 
   </p:commandButton>  
</p:column>  

The bean that ‘datlis’ represents is ViewScoped in my application – and I’ve checked that datlist.filepath is not null. And the file download bean (FileDownloader) is as follows:

@ManagedBean(name="filedownloader")
@RequestScoped
public class FileDownloader {  

private StreamedContent file; 

public StreamedContent getFile() {  
    return file;  
}

@ManagedProperty(value="#{param.filepath}")
private String filepath;

public String getFilepath() {
    return filepath;
}
public void setFilepath(String filepath) {
System.out.println("> "+filepath);
    this.filepath = filepath;
System.out.println(">> "+this.filepath);
}

public FileDownloader() throws FileNotFoundException { 
System.out.println("100");
    String filename = "/opt/glassfish3/glassfish/domains/domain1/datasets/string_compare/Business v2 Metadata/README.txt";
        InputStream stream = new FileInputStream(filepath);
        file = new DefaultStreamedContent(stream, "text/txt", "README.txt");  
}  

The stack trace mentions a nullpointer exception regarding the inputstream and that’s why I’m thinking the ‘filepath’ variable isn’t being set – plus my system output only shows the “100” from the System.out.println, and no System outputs from the setFilepath function…as if it’s not called at all.

I’ve also tried:

<p:column headerText="Metadata" style="width:40px">  
                <p:commandButton id="selectButton" rendered="#{datlis.has_metadata}" icon="ui-icon-circle-arrow-s" title="View" ajax="false" >  
                    <f:param name="filepath" value="#{datlis.filepath}" />  
                    <p:fileDownload value="#{filedownloader.file}" /> 
                </p:commandButton>  
            </p:column>

with the added code just above the filepath getter/setter in my FileDownloader class:

@ManagedProperty(value="#{param.filepath}")
private String filepath;

But this also doesn’t seem to work. Any ideas? I feel I’m on the right track perhaps just misusing the elements…

Answer 1

Managed properties will be injected after construction. So you will get an NPE if you try to access them in the bean’s constructor.

Use a method annotated with @PostConstruct. It will automatically be invoked after construction and property injection:

@PostConstruct
public void init() {
  // do your initializations here
}