Sun Java System Application Server Enterprise Edition 8.2 Upgrade and Migration Guide

Chapter 5 J2EE 1.4 Compatibility Issues

The following topics are covered in this chapter:

Binary Compatibility

The Java SDK included in Application Server 8.2 is the J2EE version 1.4 SDK. This version of the J2EE SDK is compatible with J2EE SDK, v1.3.

Source Compatibility

Downward source compatibility is not supported. If source files use new J2EE APIs, they are not usable with an earlier version of the J2EE platform.

In general, the policy is as follows:

Maintenance releases do not introduce any new APIs, so they maintain source-compatibility with one another. However, since J2EE is based on J2SE, a new Application Server release may include a new version of J2SE. For more information, refer to the J2SE document on compatibility issues:

http://java.sun.com/j2se/1.4.2/compatibility.html
Functionality releases and major releases maintain upwards but not downwards source-compatibility.

Deprecated APIs are methods and classes that are supported only for backward compatibility, and the compiler generates a warning message whenever one of these is used, unless the -nowarn command-line option is used. It is recommended that programs be modified to eliminate the use of deprecated methods and classes, though there are no plans to remove such methods and classes entirely.

Incompatibilities with the J2EE 1.4 Platform (since the J2EE 1.3 release)

The Sun Java System Application Server 8.2 release is based on the Java 2 Platform, Enterprise Edition, version 1.4. The Sun Java System Application Server 7 release is based on the Java 2 Platform, Enterprise Edition, version 1.3.

Almost all existing programs must run on the Sun Java System Application Server 8.2 release without modification. However, there are some minor potential incompatibilities that involve rare circumstances and corner cases that have been documented here for completeness.

Java Servlet Specification Version 2.4 ships with the Sun Java System Application Server 8.2 release, and can be downloaded from the following URL:

http://java.sun.com/products/servlet/

Version 2.3 of the specification shipped with the J2EE 1.3 SDK. The following items discuss compatibility issues between these releases.
- HttpSessionListener sessionDestroyed method was previously used to notify that a session was invalidated. As of this release, this method is used to notify that a session is about to be invalidated so that it notifies before the session invalidation. If the code assumed the previous behavior, it must be modified to match the new behavior.
- ServletRequest, getRemotePort, getLocalName, getLocalAddr, getLocalPort
  
  The following methods are added in the ServletRequest interface in this version of the specification. Be aware that this addition causes source incompatibility in some cases, such as when a developer implements the ServletRequest interface. In this case, ensure that all the new methods are implemented:
  - public int getRemotePort() returns the Internet Protocol (IP) source port of the client or last proxy that sent the request.
  - public java.lang.String getLocalName() returns the host name of the IP interface on which the request was received.
  - public java.lang.String getLocalAddr() returns the IP address of the interface on which the request was received.
  - public int getLocalPort() returns the IP port number of the interface on which the request was received.
  Java Server Pages (JSP) Specification 2.0 ships with the Sun Java System Application Server 8.2 release and is downloadable from the following URL:
  
  http://java.sun.com/products/jsp/
  
  JSP specification 1.2 shipped with the J2EE 1.3 SDK. Wherever possible, the JSP 2.0 specification attempts to be fully backward compatible with the JSP 1.2 specification. In some cases, there are ambiguities in the JSP 1.2 specification that have been clarified in the JSP 2.0 Specification. Because some JSP 1.2 containers behave differently, some applications that rely on container-specific behavior may need to be adjusted to work correctly in a JSP 2.0 environment.
  
  The following is a list of known backward compatibility issues related to JSP:
- Tag Library validators that are not namespace-aware and that rely solely on the prefix parameter might not correctly validate some JSP 2.0 pages. This is because the XML view might contain tag library declarations in elements other than jsp:root, and might contain the same tag library declaration more than once, using different prefixes. The uri parameter should always be used by tag library validators instead. Existing JSP pages with existing tag libraries do not create any problems.
- You may observe differences in I18N behavior on some containers primarily due to ambiguity in the JSP 1.2 specification. Where possible, steps were taken to minimize the impact on backward compatibility and overall, the I18N abilities of technology have been greatly improved.
  
  In the JSP specification versions previous to JSP 2.0, JSP pages in XML syntax and those in standard syntax determined their page encoding in the same fashion, by examining the pageEncoding or contentType attributes of their page directive, defaulting to ISO-8859-1 if neither was present.
  
  As of the JSP specification v2.0, the page encoding for JSP documents is determined as described in section 4.3.3 and appendix F.1 of the XML specification, and the pageEncoding attribute of those pages is only checked to make sure it is consistent with the page encoding determined as per the XML specification.
  
  As a result of this change, JSP documents that rely on their page encoding to be determined from their pageEncoding attribute will no longer be decoded correctly. These JSP documents must be changed to include an appropriate XML encoding declaration.
  
  Additionally, in the JSP 1.2 Specification, page encodings are determined on a per translation unit basis whereas in the JSP 2.0 Specification, page encodings are determined on a per-file basis. Therefore, if a.jsp statically includes b.jsp, and a page encoding is specified in a.jsp but not in b.jsp, in the JSP 1.2 specification a.jsp’s encoding is used for b.jsp, but in the JSP 2.0 Specification, the default encoding is used for b.jsp.
- The type coercion rules (shown in Table JSP.1-11 in the JSP 2.0 specification) have been reconciled with the EL coercion rules. There are some exceptional conditions that no longer result in an exception in the JSP 2.0 specification. In particular, when passing an empty String to an attribute of a numeric type, a translation error or a NumberFormatException used to occur, whereas in the JSP 2.0 specification, a 0 is passed in instead. See Table JSP.1-11 in the JSP 2.0 specification for details. In general, this is not expected to cause any problems because these would have been exceptional conditions in the JSP 1.2 specification and the specification allowed for these exceptions to occur at translation time or request time.
- The JSP container uses web.xml to determine the default behavior of various container features. The following is a list of items of which JSP developers should be aware when upgrading their web.xml file from Servlet version 2.3 Specification to Servlet version 2.4 Specification.
  - EL expressions are ignored by default in applications created with JSP 1.2 technology. When upgrading a Web application to the JSP 2.0 specification, EL expressions are interpreted by default. The escape sequence \\$ can be used to escape EL expressions that should not be interpreted by the container. Alternatively, the isELIgnored page directive attribute, or the el-ignored configuration element can deactivate EL for entire translation units. Users of JSTL 1.0 need to either upgrade their taglib/ imports to the JSTL 1.1 URIs, or they need to use the _rt versions of the tags (for example c_rt instead of c, or fmt_rt instead of fmt).
  - Files with an extension of .jspx are interpreted as JSP documents by default. Use the JSP configuration element is-xml to treat .jspx files as regular JSP pages. There is no way to disassociate .jspx from the JSP container.
  - The escape sequence \\$ was not reserved in the JSP 1.2 specification. Any template text or attribute value that appeared as \\$ in the JSP 1.2 specification used to output \\$ but now outputs just $.

JAXP and SAX Incompatibilities

Sun Java System Application Server 8.2 supports JAXP 1.3, which in turn supports SAX 2.0.2. In SAX 2.0.2, DeclHandler.externalEntityDecl requires the parser to return the absolute system identifier for consistency with DTDHandler.unparsedEntityDecl. This might cause some incompatibilities when migrating applications that use SAX 2.0.0.

To migrate an application that uses SAX 2.0.0 to SAX 2.0.2 without changing the previous behavior of externalEntityDecl, you can set the resolve-dtd-uris feature to false. For example:

SAXParserFactory spf = SAXParserFactory.newInstance();
spf.setFeature("http://xml.org/sax/features/resolve-dtd-uris",false);

Other incompatibilities between SAX 2.0.0 and SAX 2.0.2 are documented in the JAXP Compatibility Guide.

The `pass-by-reference` Element

Sun Java System Application Server 8.2 is compatible with the Java 2 Platform, Enterprise Edition specification by default. In this case, all portable J2EE programs run on the Application Server without modification. However, as allowed by the J2EE compatibility requirements, it is possible to configure applications to use features of the Sun Java System Application Server 8.2 that are not compatible with the J2EE specification.

The pass-by-reference element in the sun-ejb-jar.xml file only applies to remote calls. As defined in the EJB 2.0 specification, section 5.4, calls to local interfaces use pass-by-reference semantics.

If the pass-by-reference element is set to its default value of false, the parameter passing semantics for calls to remote interfaces comply with the EJB 2.0 specification, section 5.4. If set to true, remote calls involve pass-by-reference semantics instead of pass-by-value semantics, contrary to this specification.

Portable programs cannot assume that a copy of the object is made during such a call, and thus that it is safe to modify the original. Nor can they assume that a copy is not made, and thus that changes to the object are visible to both caller and callee. When this flag is set to true, parameters and return values are considered read-only. The behavior of a program that modifies such parameters or return values is undefined. For more information about the pass-by-reference element, see the Sun Java System Application Server Enterprise Edition 8.2 Developer’s Guide.