EJB Bad Practices: Use of Java I/O

Description

The Enterprise JavaBeans specification requires that every bean provider follow a set of programming guidelines designed to ensure that the bean will be portable and behave consistently in any EJB container. In this case, the product violates the following EJB guideline: "An enterprise bean must not use the java.io package to attempt to access files and directories in the file system." The specification justifies this requirement in the following way: "The file system APIs are not well-suited for business components to access data. Business components should use a resource manager API, such as JDBC, to store data."

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

The following Java example is a simple stateless Enterprise JavaBean that retrieves the interest rate for the number of points for a mortgage. In this example, the interest rates for various points are retrieved from an XML document on the local file system, and the EJB uses the Java I/O API to retrieve the XML document from the local file system.

@Stateless
public class InterestRateBean implements InterestRateRemote {


  private Document interestRateXMLDocument = null;
  private File interestRateFile = null;

  public InterestRateBean() {

    try {


      /* get XML document from the local filesystem */
      interestRateFile = new File(Constants.INTEREST_RATE_FILE);

      if (interestRateFile.exists())
      {
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = dbf.newDocumentBuilder();
        interestRateXMLDocument = db.parse(interestRateFile);
      }

    } catch (IOException ex) {...}

  }

  public BigDecimal getInterestRate(Integer points) {
    return getInterestRateFromXML(points);
  }

  /* member function to retrieve interest rate from XML document on the local file system */

  private BigDecimal getInterestRateFromXML(Integer points) {...}

}

This use of the Java I/O API within any kind of Enterprise JavaBean violates the EJB specification by using the java.io package for accessing files within the local filesystem.

An Enterprise JavaBean should use a resource manager API for storing and accessing data. In the following example, the private member function getInterestRateFromXMLParser uses an XML parser API to retrieve the interest rates.

@Stateless
public class InterestRateBean implements InterestRateRemote {


  public InterestRateBean() {
  }

  public BigDecimal getInterestRate(Integer points) {
    return getInterestRateFromXMLParser(points);
  }

  /* member function to retrieve interest rate from XML document using an XML parser API */

  private BigDecimal getInterestRateFromXMLParser(Integer points) {...}

}

See Also