TOMCAT-NEXT.txt

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Notes of things to consider for the next major Tomcat release (probably 8.0.x
but possibly 7.1.x).

 1. Refactor the TLD parsing. TLDs are currently parsed twice. Once by Catalina
    looking for listeners and once by Jasper.
    - Complete

 2. Refactor the XML parsing (org.apache.tomcat.util.xml ?) to remove duplicate
    XML parsing code in Catalina and Jasper such as the entity resolvers used
    for validation.
    - Partial.
    - More sharing possible?

 3. TLDs may have a many to many relationship between URIs and TLD files. This
    can result in the same TLD file being parsed many times. Refactor the
    TldLocationCache to cache the parsed nodes (will need to check for changes
    to TLD files).
    - Complete

 4. TLD files should be included in the dependencies for JSP and Tag files.
    - Complete

 5. Run the unused code detector and remove everything that isn't currently used.
    Add deprecation markers for the removed code to Tomcat 7.0.x
    - Complete

 6. Change the default URIEncoding on the connector to UTF-8.
    - Complete

 7. Rip out all the JNDI code in resource handling and replace it with straight
    URLs (File or WAR).
    - Complete

    kkolinko: I think this proposal goes too far. There are several
    separate issues. There are:

    a) Internal API to define resources
     - BaseDirContext implementing aliases and resource jars,
     and there will be overlays in Servlet 3.1
     - StandardContext.setResources() allowing an arbitrary DirContext
     implementation via <Resources> element.

     Concerns:
     - Too many ways to configure it.

    b) Internal API to lookup resources
     - DirContext interface

     Concerns:
     - Unnecessary objects, e.g. NamingException instead of null.

     - Too many methods. Name vs. String. list() vs. listBindings().

     - Limited API. As a workaround, there are non-standard methods that
       are implemented on BaseDirContext instead, e.g. getRealPath(),
       doListBindings(..).

     - All caching (ProxyDirContext) and aliases handling is
     performed on the root level only.

     Once I do a lookup that returns a DirContext, further lookups on it
     will bypass the caching and aliases.

    c) WebappClassLoader and its interaction with resources

     WebappClassLoader uses DirContext API to access resources (classes,
     jars).

     Note that it has to construct a classpath for Java compiler called by
     Jasper. The compiler cannot operate on a DirContext and needs access
     to actual files and JARs.

     Concerns:
     - There are problems with access to classes and JAR files in
     non-unpacked WARs.

     It is resolved by unzipping the files into the working directory (in
     WebappLoader#setRepositories()).

     Note that DirContext is not notified of this copying.
     StandardJarScanner does not know of those copies either.

     - There are problems when the classes directory is served from
     multiple locations

     It seems to be worked around by adding the path of the alternative
     classes directory to virtualClasspath of VirtualWebappLoader (as shown
     by example in config/context.html#Virtual_webapp), but it is likely
     that I miss something.

     - antiJARLocking support in WebappClassLoader creates copies of
     resources, but does not notify the DirContext.

     - WebappClassLoader.jarFiles is used to track JAR files and keep them
     open. These might be useful when looking for resources in those files.
     These might be useful for StandardJarScanner.

    d) StandardJarScanner

     Concerns:
     - It essentially scans the same JARs as accessed by WebappClassLoader.

     It might be better to access them via WebappClassLoader rather that
     through Servlet API methods.

     The scanner is used by Jasper as well, so there are some concerns to
     keep the components independent.

    e) URL returned by ServletContext.getResource()
     jndi:/hostName/contextPath/resourcePath

     Goodies:
     - Uniform URL space. Both files and directories can be represented,
     hiding details of aliases, resource jars, etc.

     - It hides implementation details.

     - Permissions can be expressed as JndiPermission. They do not depend
     on context version number.

     - Accessing a resource through such URL leverages the cache
     implemented in ProxyDirContext class. We do not access the file system
     directly, nor need to open a JAR file.

     - It can be created from a String if necessary.

     Such use relies on DirContextURLStreamHandler.bindThread(..) being
     called earlier in the same thread.

     Concerns:
     - Some components would like to get "real" resource URL from this one.

     Maybe it can be exposed through some special header name,
     DirContextURLConnection.getHeaderField(str)?

     How such real URL can be prepared?
     DirContext.getNameInNamespace()?
     BaseDirContext.getRealPath()?
     ((FileResourceAttributes)DirContext.getAttributes()).getCanonicalPath()?

     - A resource lookup is performed twice. The first time in
     ServletContext.getResource() (implemented in ApplicationContext.getResource())
     to return null for non-existing paths.
     The second time in DirContextURLConnection.connect().

     It is good that there is a cache in ProxyDirContext that saves time
     for repeated lookups.

     - Using URLs involves encoding/decoding.

     If there were some other API to access resources in a web application,
     I would prefer some opaque object that allows access to resource
     properties, but is converted to string/url form only on demand.

    f) Connection, created from jndi: URL
     DirContextURLStreamHandler, DirContextURLConnection

     Goodies:
     - DirContextURLConnection provides information about resource via
     methods such as getContentLength(), getHeaderField(str).

     Concerns:
     - It exposes DirContext through some APIs, such as
     DirContextURLConnection.getContent().

     Is this feature going to be preserved for compatibility, or to be
     removed?

     - DirContextURLConnection.list(): a public method, that is not part of
     the usual URL API. So URL API is lacking. Maybe some other methods
     could be added.

     A possible candidate could be "isCollection()", instead of asking for
     getContentType() and checking its value against ResourceAttributes.COLLECTION_TYPE.

    Threads:
    http://markmail.org/thread/hqbmdn2qs6xcooko

 8. Review the connector shutdown code for timing and threading issues
    particularly any that may result in a client socket being left open after a
    connector.stop().
    - Complete.

 9. Remove the svn keywords from all the files. (Just Java files?)

10. Code to the interfaces in the o.a.catalina package and avoid coding directly
    to implementations in other packages. This is likely to require a lot of
    work. Maybe use Structure 101 (or similar) to help.
    - Partially complete - probably as far as is practical.

11. Merge Service and Engine
    - Decided not to do this.

12. Java 7 updates
    - Use of <> operator where possible
      - Complete
    - Use of try with resources
      - Not started
    - Catching multiple exceptions
      - Not started

13. Fix all FindBugs warnings
    - Complete

14. Review date formatting with a view to reducing duplication.