resources.xml

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  <title>Resources</title>

  <section xml:id="resources-introduction">
    <title>Introduction</title>

    <para>Java's standard <classname>java.net.URL</classname> class and
    standard handlers for various URL prefixes unfortunately are not quite
    adequate enough for all access to low-level resources. For example,
    there is no standardized <classname>URL</classname> implementation
    that may be used to access a resource that needs to be obtained from
    the classpath, or relative to a
    <interfacename>ServletContext</interfacename>. While it is possible
    to register new handlers for specialized <classname>URL</classname>
    prefixes (similar to existing handlers for prefixes such as
    <literal>http:</literal>), this is generally quite complicated, and the
    <classname>URL</classname> interface still lacks some desirable
    functionality, such as a method to check for the existence of the
    resource being pointed to.</para>
  </section>

  <section xml:id="resources-resource">
    <title>The <interfacename>Resource</interfacename> interface</title>

    <para>Spring's <interfacename>Resource</interfacename> interface is meant
    to be a more capable interface for abstracting access to low-level
    resources.</para>

    <programlisting language="java"><![CDATA[public interface Resource extends InputStreamSource {

    boolean exists();

    boolean isOpen();

    URL getURL() throws IOException;

    File getFile() throws IOException;

    Resource createRelative(String relativePath) throws IOException;

    String getFilename();

    String getDescription();
}]]></programlisting>

    <programlisting language="java"><![CDATA[public interface InputStreamSource {

    InputStream getInputStream() throws IOException;
}]]></programlisting>

    <para>Some of the most important methods from the
    <interfacename>Resource</interfacename> interface are:</para>

    <itemizedlist>
      <listitem>
        <para><methodname>getInputStream()</methodname>: locates and opens the
        resource, returning an <classname>InputStream</classname> for reading
        from the resource. It is expected that each invocation returns a
        fresh <classname>InputStream</classname>. It is the responsibility of
        the caller to close the stream.</para>
      </listitem>

      <listitem>
        <para><methodname>exists()</methodname>: returns a
        <literal>boolean</literal> indicating whether this resource actually
        exists in physical form.</para>
      </listitem>

      <listitem>
        <para><methodname>isOpen()</methodname>: returns a
        <literal>boolean</literal> indicating whether this resource represents
        a handle with an open stream. If <literal>true</literal>, the
        <classname>InputStream</classname> cannot be read multiple times, and
        must be read once only and then closed to avoid resource leaks. Will
        be <literal>false</literal> for all usual resource implementations,
        with the exception of
        <classname>InputStreamResource</classname>.</para>
      </listitem>

      <listitem>
        <para><methodname>getDescription()</methodname>: returns a description
        for this resource, to be used for error output when working with the
        resource. This is often the fully qualified file name or the actual
        URL of the resource.</para>
      </listitem>
    </itemizedlist>

    <para>Other methods allow you to obtain an actual
    <classname>URL</classname> or <classname>File</classname> object
    representing the resource (if the underlying implementation is compatible,
    and supports that functionality).</para>

    <para>The <interfacename>Resource</interfacename> abstraction is used
    extensively in Spring itself, as an argument type in many method
    signatures when a resource is needed. Other methods in some Spring APIs
    (such as the constructors to various
    <interfacename>ApplicationContext</interfacename> implementations), take a
    <classname>String</classname> which in unadorned or simple form is used to
    create a <interfacename>Resource</interfacename> appropriate to that
    context implementation, or via special prefixes on the
    <classname>String</classname> path, allow the caller to specify that a
    specific <interfacename>Resource</interfacename> implementation must be
    created and used.</para>

    <para>While the <interfacename>Resource</interfacename> interface is used
    a lot with Spring and by Spring, it's actually very useful to use as a
    general utility class by itself in your own code, for access to resources,
    even when your code doesn't know or care about any other parts of Spring.
    While this couples your code to Spring, it really only couples it to this
    small set of utility classes, which are serving as a more capable
    replacement for <classname>URL</classname>, and can be considered
    equivalent to any other library you would use for this purpose.</para>

    <para>It is important to note that the
    <interfacename>Resource</interfacename> abstraction does not replace
    functionality: it wraps it where possible. For example, a
    <classname>UrlResource</classname> wraps a URL, and uses the wrapped
    <classname>URL</classname> to do its work.</para>
  </section>

  <section xml:id="resources-implementations">
    <title>Built-in <interfacename>Resource</interfacename> implementations</title>

    <para>There are a number of <interfacename>Resource</interfacename>
    implementations that come supplied straight out of the box in
    Spring:</para>

    <section xml:id="resources-implementations-urlresource">
      <title><classname>UrlResource</classname></title>

      <para>The <classname>UrlResource</classname> wraps a
      <classname>java.net.URL</classname>, and may be used to access any
      object that is normally accessible via a URL, such as files, an HTTP
      target, an FTP target, etc. All URLs have a standardized
      <classname>String</classname> representation, such that appropriate
      standardized prefixes are used to indicate one URL type from another.
      This includes <literal>file:</literal> for accessing filesystem paths,
      <literal>http:</literal> for accessing resources via the HTTP protocol,
      <literal>ftp:</literal> for accessing resources via FTP, etc.</para>

      <para>A <classname>UrlResource</classname> is created by Java code
      explicitly using the <classname>UrlResource</classname> constructor, but
      will often be created implicitly when you call an API method which takes
      a <classname>String</classname> argument which is meant to represent a
      path. For the latter case, a JavaBeans
      <interfacename>PropertyEditor</interfacename> will ultimately decide
      which type of <interfacename>Resource</interfacename> to create. If the
      path string contains a few well-known (to it, that is) prefixes such as
      <literal>classpath:</literal>, it will create an appropriate specialized
      <interfacename>Resource</interfacename> for that prefix. However, if it
      doesn't recognize the prefix, it will assume the this is just a standard
      URL string, and will create a <classname>UrlResource</classname>.</para>
    </section>

    <section xml:id="resources-implementations-classpathresource">
      <title><classname>ClassPathResource</classname></title>

      <para>This class represents a resource which should be obtained from the
      classpath. This uses either the thread context class loader, a given
      class loader, or a given class for loading resources.</para>

      <para>This <interfacename>Resource</interfacename> implementation
      supports resolution as <classname>java.io.File</classname> if the class
      path resource resides in the file system, but not for classpath
      resources which reside in a jar and have not been expanded (by the
      servlet engine, or whatever the environment is) to the filesystem. To
      address this the various <interfacename>Resource</interfacename>
      implementations always support resolution as a
      <classname>java.net.URL</classname>.</para>

      <para>A <classname>ClassPathResource</classname> is created by Java code
      explicitly using the <classname>ClassPathResource</classname>
      constructor, but will often be created implicitly when you call an API
      method which takes a <classname>String</classname> argument which is
      meant to represent a path. For the latter case, a JavaBeans
      <interfacename>PropertyEditor</interfacename> will recognize the special
      prefix <literal>classpath:</literal>on the string path, and create a
      <classname>ClassPathResource</classname> in that case.</para>
    </section>

    <section xml:id="resources-implementations-filesystemresource">
      <title><classname>FileSystemResource</classname></title>

      <para>This is a <interfacename>Resource</interfacename> implementation
      for <classname>java.io.File</classname> handles. It obviously supports
      resolution as a <classname>File</classname>, and as a
      <classname>URL</classname>.</para>
    </section>

    <section xml:id="resources-implementations-servletcontextresource">
      <title><classname>ServletContextResource</classname></title>

      <para>This is a <interfacename>Resource</interfacename> implementation
      for <interfacename>ServletContext</interfacename> resources,
      interpreting relative paths within the relevant web application's root
      directory.</para>

      <para>This always supports stream access and URL access, but only allows
      <classname>java.io.File</classname> access when the web application
      archive is expanded and the resource is physically on the filesystem.
      Whether or not it's expanded and on the filesystem like this, or
      accessed directly from the JAR or somewhere else like a DB (it's
      conceivable) is actually dependent on the Servlet container.</para>
    </section>

    <section xml:id="resources-implementations-inputstreamresource">
      <title><classname>InputStreamResource</classname></title>

      <para>A <interfacename>Resource</interfacename> implementation for a
      given <interfacename>InputStream</interfacename>. This should only be
      used if no specific <interfacename>Resource</interfacename>
      implementation is applicable. In particular, prefer
      <classname>ByteArrayResource</classname> or any of the file-based
      <interfacename>Resource</interfacename> implementations where
      possible.</para>

      <para>In contrast to other <interfacename>Resource</interfacename>
      implementations, this is a descriptor for an
      <emphasis>already</emphasis> opened resource - therefore returning
      <literal>true</literal> from <methodname>isOpen()</methodname>. Do not
      use it if you need to keep the resource descriptor somewhere, or if you
      need to read a stream multiple times.</para>
    </section>

    <section xml:id="resources-implementations-bytearrayresource">
      <title><classname>ByteArrayResource</classname></title>

      <para>This is a <interfacename>Resource</interfacename> implementation
      for a given byte array. It creates a
      <classname>ByteArrayInputStream</classname> for the given byte
      array.</para>

      <para>It's useful for loading content from any given byte array, without
      having to resort to a single-use
      <classname>InputStreamResource</classname>.</para>
    </section>
  </section>

  <section xml:id="resources-resourceloader">
    <title>The <interfacename>ResourceLoader</interfacename></title>

    <para>The <interfacename>ResourceLoader</interfacename> interface is meant
    to be implemented by objects that can return (i.e. load)
    <interfacename>Resource</interfacename> instances.</para>

    <programlisting language="java">public interface ResourceLoader {
    Resource getResource(String location);
}</programlisting>

    <para>All application contexts implement the
    <interfacename>ResourceLoader</interfacename> interface, and therefore all
    application contexts may be used to obtain
    <interfacename>Resource</interfacename> instances.</para>

    <para>When you call <methodname>getResource()</methodname> on a specific
    application context, and the location path specified doesn't have a
    specific prefix, you will get back a
    <interfacename>Resource</interfacename> type that is appropriate to that
    particular application context. For example, assume the following snippet
    of code was executed against a
    <classname>ClassPathXmlApplicationContext</classname> instance:</para>

    <programlisting language="java">Resource template = ctx.getResource("some/resource/path/myTemplate.txt");</programlisting>

    <para>What would be returned would be a
    <classname>ClassPathResource</classname>; if the same method was executed
    against a <classname>FileSystemXmlApplicationContext</classname> instance,
    you'd get back a <classname>FileSystemResource</classname>. For a
    <classname>WebApplicationContext</classname>, you'd get back a
    <classname>ServletContextResource</classname>, and so on.</para>

    <para>As such, you can load resources in a fashion appropriate to the
    particular application context.</para>

    <para>On the other hand, you may also force
    <classname>ClassPathResource</classname> to be used, regardless of the
    application context type, by specifying the special
    <literal>classpath:</literal> prefix:</para>

    <programlisting language="java">Resource template = ctx.getResource("classpath:some/resource/path/myTemplate.txt");</programlisting>

    <para>Similarly, one can force a <classname>UrlResource</classname> to be
    used by specifying any of the standard <classname>java.net.URL</classname>
    prefixes:</para>

    <programlisting language="java">Resource template = ctx.getResource("file:/some/resource/path/myTemplate.txt");</programlisting>

    <programlisting language="java">Resource template = ctx.getResource("http://myhost.com/resource/path/myTemplate.txt");</programlisting>

    <para>The following table summarizes the strategy for converting
    <classname>String</classname>s to
    <interfacename>Resource</interfacename>s:</para>

    <table pgwide="1" xml:id="resources-resource-strings">
      <title>Resource strings</title>

      <tgroup cols="3">
        <colspec align="left" />

        <thead>
          <row>
            <entry align="center">Prefix</entry>

            <entry align="center">Example</entry>

            <entry align="center">Explanation</entry>
          </row>
        </thead>

        <tbody>
          <row>
            <entry><para>classpath:</para></entry>

            <entry><para> <literal>classpath:com/myapp/config.xml</literal>
            </para></entry>

            <entry><para>Loaded from the classpath.</para></entry>
          </row>

          <row>
            <entry><para>file:</para></entry>

            <entry><para> <literal>file:/data/config.xml</literal>
            </para></entry>

            <entry><para> Loaded as a <classname>URL</classname>, from the
            filesystem. <footnote>
                <para>But see also
                <xref linkend="resources-filesystemresource-caveats" />.</para>
              </footnote> </para></entry>
          </row>

          <row>
            <entry><para>http:</para></entry>

            <entry><para> <literal>http://myserver/logo.png</literal>
            </para></entry>

            <entry><para>Loaded as a
            <classname>URL</classname>.</para></entry>
          </row>

          <row>
            <entry><para>(none)</para></entry>

            <entry><para> <literal>/data/config.xml</literal> </para></entry>

            <entry><para> Depends on the underlying
            <interfacename>ApplicationContext</interfacename>. </para></entry>
          </row>
        </tbody>
      </tgroup>
    </table>
  </section>

  <section xml:id="resources-resourceloaderaware">
    <title>The <interfacename>ResourceLoaderAware</interfacename> interface</title>

    <para>The <interfacename>ResourceLoaderAware</interfacename> interface is
    a special marker interface, identifying objects that expect to be provided
    with a <interfacename>ResourceLoader</interfacename> reference.</para>

    <programlisting language="java"><![CDATA[public interface ResourceLoaderAware {

   void setResourceLoader(ResourceLoader resourceLoader);
}]]></programlisting>

    <para>When a class implements
    <interfacename>ResourceLoaderAware</interfacename> and is deployed into an
    application context (as a Spring-managed bean), it is recognized as
    <interfacename>ResourceLoaderAware</interfacename> by the application
    context. The application context will then invoke the
    <methodname>setResourceLoader(ResourceLoader)</methodname>, supplying
    itself as the argument (remember, all application contexts in Spring
    implement the <interfacename>ResourceLoader</interfacename>
    interface).</para>

    <para>Of course, since an
    <interfacename>ApplicationContext</interfacename> is a
    <interfacename>ResourceLoader</interfacename>, the bean could also
    implement the <interfacename>ApplicationContextAware</interfacename>
    interface and use the supplied application context directly to load
    resources, but in general, it's better to use the specialized
    <interfacename>ResourceLoader</interfacename> interface if that's all
    that's needed. The code would just be coupled to the resource loading
    interface, which can be considered a utility interface, and not the whole
    Spring <interfacename>ApplicationContext</interfacename> interface.</para>

    <para>As of Spring 2.5, you can rely upon autowiring of the
    <interfacename>ResourceLoader</interfacename> as an alternative to
    implementing the <interfacename>ResourceLoaderAware</interfacename> interface.
    The "traditional" <literal>constructor</literal> and <literal>byType</literal>
    autowiring modes (as described in <xref linkend="beans-factory-autowire"/>)
    are now capable of providing a dependency of type
    <interfacename>ResourceLoader</interfacename> for either a
    constructor argument or setter method parameter respectively. For more flexibility
    (including the ability to autowire fields and multiple parameter methods), consider
    using the new annotation-based autowiring features. In that case, the
    <interfacename>ResourceLoader</interfacename> will be autowired into a field,
    constructor argument, or method parameter that is expecting the
    <interfacename>ResourceLoader</interfacename> type as long as the field,
    constructor, or method in question carries the
    <interfacename>@Autowired</interfacename> annotation. For more information,
    see <xref linkend="beans-autowired-annotation"/>.</para>
  </section>

  <section xml:id="resources-as-dependencies">
    <title><literal>Resources</literal> as dependencies</title>

    <para>If the bean itself is going to determine and supply the resource
    path through some sort of dynamic process, it probably makes sense for the
    bean to use the <interfacename>ResourceLoader</interfacename> interface to
    load resources. Consider as an example the loading of a template of some
    sort, where the specific resource that is needed depends on the role of
    the user. If the resources are static, it makes sense to eliminate the use
    of the <interfacename>ResourceLoader</interfacename> interface completely,
    and just have the bean expose the <interfacename>Resource</interfacename>
    properties it needs, and expect that they will be injected into it.</para>

    <para>What makes it trivial to then inject these properties, is that all
    application contexts register and use a special JavaBeans
    <interfacename>PropertyEditor</interfacename> which can convert
    <classname>String</classname> paths to
    <interfacename>Resource</interfacename> objects. So if
    <literal>myBean</literal> has a template property of type
    <interfacename>Resource</interfacename>, it can be configured with a
    simple string for that resource, as follows:</para>

    <programlisting language="xml"><![CDATA[<bean id="myBean" class="...">
  <property name="template" value="some/resource/path/myTemplate.txt"/>
</bean>]]></programlisting>

    <para>Note that the resource path has no prefix, so because the
    application context itself is going to be used as the
    <interfacename>ResourceLoader</interfacename>, the resource itself will be
    loaded via a <classname>ClassPathResource</classname>,
    <literal>FileSystemResource</literal>, or
    <classname>ServletContextResource</classname> (as appropriate)
    depending on the exact type of the context.</para>

    <para>If there is a need to force a specific
    <interfacename>Resource</interfacename> type to be used, then a prefix may
    be used. The following two examples show how to force a
    <classname>ClassPathResource</classname> and a
    <classname>UrlResource</classname> (the latter being used to access a
    filesystem file).</para>

    <programlisting language="xml"><![CDATA[<property name="template" value="classpath:some/resource/path/myTemplate.txt">]]></programlisting>

    <programlisting language="xml"><![CDATA[<property name="template" value="file:/some/resource/path/myTemplate.txt"/>]]></programlisting>
  </section>

  <section xml:id="resources-app-ctx">
    <title>Application contexts and <interfacename>Resource</interfacename> paths</title>

    <section xml:id="resources-app-ctx-construction">
      <title>Constructing application contexts</title>

      <para>An application context constructor (for a specific application
      context type) generally takes a string or array of strings as the
      location path(s) of the resource(s) such as XML files that make up the
      definition of the context.</para>

      <para>When such a location path doesn't have a prefix, the specific
      <interfacename>Resource</interfacename> type built from that path and
      used to load the bean definitions, depends on and is appropriate to the
      specific application context. For example, if you create a
      <classname>ClassPathXmlApplicationContext</classname> as follows:</para>

      <programlisting language="java"><![CDATA[ApplicationContext ctx = new ClassPathXmlApplicationContext("conf/appContext.xml");]]></programlisting>

      <para>The bean definitions will be loaded from the classpath, as a
      <classname></classname><classname>ClassPathResource</classname> will be
      used. But if you create a
      <classname>FileSystemXmlApplicationContext</classname> as
      follows:</para>

      <programlisting language="java"><![CDATA[ApplicationContext ctx =
    new FileSystemXmlApplicationContext("conf/appContext.xml");]]></programlisting>

      <para>The bean definition will be loaded from a filesystem location, in
      this case relative to the current working directory.</para>

      <para>Note that the use of the special classpath prefix or a standard
      URL prefix on the location path will override the default type of
      <interfacename>Resource</interfacename> created to load the definition.
      So this <classname>FileSystemXmlApplicationContext</classname>...</para>

      <programlisting language="java"><![CDATA[ApplicationContext ctx =
    new FileSystemXmlApplicationContext("classpath:conf/appContext.xml");]]></programlisting>

      <para>... will actually load its bean definitions from the classpath.
      However, it is still a <classname>FileSystemXmlApplicationContext</classname>. If it is
      subsequently used as a <interfacename>ResourceLoader</interfacename>,
      any unprefixed paths will still be treated as filesystem paths.</para>

      <section xml:id="resources-app-ctx-classpathxml">
        <title>Constructing <classname>ClassPathXmlApplicationContext</classname> instances - shortcuts</title>

        <para>The <classname>ClassPathXmlApplicationContext</classname>
        exposes a number of constructors to enable convenient instantiation.
        The basic idea is that one supplies merely a string array containing
        just the filenames of the XML files themselves (without the leading
        path information), and one <emphasis>also</emphasis> supplies a
        <classname>Class</classname>; the
        <classname>ClassPathXmlApplicationContext</classname> will derive the
        path information from the supplied class.</para>

        <para>An example will hopefully make this clear. Consider a directory
        layout that looks like this:</para>

        <programlisting><![CDATA[com/
  foo/
    services.xml
    daos.xml
    MessengerService.class]]></programlisting>

        <para>A <classname>ClassPathXmlApplicationContext</classname> instance
        composed of the beans defined in the <literal>'services.xml'</literal>
        and <literal>'daos.xml'</literal> could be instantiated like
        so...</para>

        <programlisting language="java"><![CDATA[ApplicationContext ctx = new ClassPathXmlApplicationContext(
    new String[] {"services.xml", "daos.xml"}, MessengerService.class);]]></programlisting>

        <para>Please do consult the Javadocs for the
        <classname>ClassPathXmlApplicationContext</classname> class for
        details of the various constructors.</para>
      </section>
    </section>

    <section xml:id="resources-app-ctx-wildcards-in-resource-paths">
      <title>Wildcards in application context constructor resource paths</title>

      <para>The resource paths in application context constructor values may
      be a simple path (as shown above) which has a one-to-one mapping to a
      target Resource, or alternately may contain the special "classpath*:"
      prefix and/or internal Ant-style regular expressions (matched using
      Spring's <classname>PathMatcher</classname> utility). Both of the latter
      are effectively wildcards</para>

      <para>One use for this mechanism is when doing component-style
      application assembly. All components can 'publish' context definition
      fragments to a well-known location path, and when the final application
      context is created using the same path prefixed via
      <literal>classpath*:</literal>, all component fragments will be picked
      up automatically.</para>

      <para>Note that this wildcarding is specific to use of resource paths in
      application context constructors (or when using the
      <classname>PathMatcher</classname> utility class hierarchy directly),
      and is resolved at construction time. It has nothing to do with the
      <interfacename>Resource</interfacename> type itself. It's not possible
      to use the <literal>classpath*:</literal> prefix to construct an actual
      <interfacename>Resource</interfacename>, as a resource points to just
      one resource at a time.</para>

      <section xml:id="resources-app-ctx-ant-patterns-in-paths">
        <title>Ant-style Patterns</title>

        <para>When the path location contains an Ant-style pattern, for example:</para>

        <programlisting><![CDATA[     /WEB-INF/*-context.xml
     com/mycompany/**/applicationContext.xml
     file:C:/some/path/*-context.xml
     classpath:com/mycompany/**/applicationContext.xml]]></programlisting>

        <para>... the resolver follows a more complex but defined procedure to
        try to resolve the wildcard. It produces a Resource for the path up to
        the last non-wildcard segment and obtains a URL from it. If this URL
        is not a "jar:" URL or container-specific variant (e.g.
        "<literal>zip:</literal>" in WebLogic, "<literal>wsjar</literal>" in
        WebSphere, etc.), then a <classname>java.io.File</classname> is
        obtained from it and used to resolve the wildcard by traversing the
        filesystem. In the case of a jar URL, the resolver either gets a
        <classname>java.net.JarURLConnection</classname> from it or manually
        parses the jar URL and then traverses the contents of the jar file
        to resolve the wildcards.</para>

        <section xml:id="resources-app-ctx-portability">
          <title>Implications on portability</title>

          <para>If the specified path is already a file URL (either
          explicitly, or implicitly because the base
          <interfacename>ResourceLoader</interfacename> is a
          filesystem one, then wildcarding is guaranteed to work in a
          completely portable fashion.</para>

          <para>If the specified path is a classpath location, then the
          resolver must obtain the last non-wildcard path segment URL via a
          <methodname>Classloader.getResource()</methodname> call. Since this
          is just a node of the path (not the file at the end) it is actually
          undefined (in the <classname>ClassLoader</classname> Javadocs)
          exactly what sort of a URL is returned in this case. In practice, it
          is always a <classname>java.io.File</classname> representing the
          directory, where the classpath resource resolves to a filesystem
          location, or a jar URL of some sort, where the classpath resource
          resolves to a jar location. Still, there is a portability concern on
          this operation.</para>

          <para>If a jar URL is obtained for the last non-wildcard segment,
          the resolver must be able to get a
          <classname>java.net.JarURLConnection</classname> from it, or
          manually parse the jar URL, to be able to walk the contents of the
          jar, and resolve the wildcard. This will work in most environments,
          but will fail in others, and it is strongly recommended that the
          wildcard resolution of resources coming from jars be thoroughly
          tested in your specific environment before you rely on it.</para>
        </section>
      </section>

      <section xml:id="resources-classpath-wildcards">
        <title>The <literal>classpath*:</literal> prefix</title>

        <para>When constructing an XML-based application context, a location
        string may use the special <literal>classpath*:</literal>
        prefix:</para>

        <programlisting language="java"><![CDATA[ApplicationContext ctx =
    new ClassPathXmlApplicationContext("classpath*:conf/appContext.xml");]]></programlisting>

        <para>This special prefix specifies that all classpath resources that
        match the given name must be obtained (internally, this essentially
        happens via a <methodname>ClassLoader.getResources(...)</methodname>
        call), and then merged to form the final application context
        definition.</para>

        <note>
          <title>Classpath*: portability</title>

          <para>The wildcard classpath relies on the <literal>getResources()</literal> method of the
          underlying classloader. As most application servers nowadays supply
          their own classloader implementation, the behavior might differ
          especially when dealing with jar files. A simple test to check if
          <literal>classpath*</literal> works is to use the classloader to load a file from
          within a jar on the classpath:
          <literal>getClass().getClassLoader().getResources("&lt;someFileInsideTheJar&gt;")</literal>.
          Try this test with files that have the same name but are placed
          inside two different locations. In case an inappropriate result is
          returned, check the application server documentation for settings
          that might affect the classloader behavior.</para>
        </note>

        <para>The "<literal>classpath*:</literal>" prefix can also be combined
        with a <literal>PathMatcher</literal> pattern in the rest of the location path, for
        example "<literal>classpath*:META-INF/*-beans.xml</literal>". In this
        case, the resolution strategy is fairly simple: a
        ClassLoader.getResources() call is used on the last non-wildcard path
        segment to get all the matching resources in the class loader
        hierarchy, and then off each resource the same PathMatcher resolution
        strategy described above is used for the wildcard subpath.</para>
      </section>

      <section xml:id="resources-wildcards-in-path-other-stuff">
        <title>Other notes relating to wildcards</title>

        <para>Please note that "<literal>classpath*:</literal>" when
        combined with Ant-style patterns will only work reliably with at least
        one root directory before the pattern starts, unless the actual target
        files reside in the file system. This means that a pattern like
        "<literal>classpath*:*.xml</literal>" will not retrieve files from the
        root of jar files but rather only from the root of expanded
        directories. This originates from a limitation in the JDK's
        <methodname>ClassLoader.getResources()</methodname> method which only
        returns file system locations for a passed-in empty string (indicating
        potential roots to search).</para>

        <para>Ant-style patterns with "<literal>classpath:</literal>"
        resources are not guaranteed to find matching resources if the root
        package to search is available in multiple class path locations. This
        is because a resource such as</para>

        <programlisting><![CDATA[    com/mycompany/package1/service-context.xml]]></programlisting>

        <para>may be in only one location, but when a path such as</para>

        <programlisting><![CDATA[    classpath:com/mycompany/**/service-context.xml]]></programlisting>

        <para>is used to try to resolve it, the resolver will work off the (first) URL
        returned by <methodname>getResource("com/mycompany")</methodname>;. If
        this base package node exists in multiple classloader locations, the
        actual end resource may not be underneath. Therefore, preferably, use
        "<literal>classpath*:</literal>" with the same Ant-style pattern in
        such a case, which will search all class path locations that contain
        the root package.</para>
      </section>
    </section>

    <section xml:id="resources-filesystemresource-caveats">
      <title><classname>FileSystemResource</classname> caveats</title>

      <para>A <classname>FileSystemResource</classname> that is not attached
      to a <classname>FileSystemApplicationContext</classname> (that is, a
      <classname>FileSystemApplicationContext</classname> is not the actual
      <interfacename>ResourceLoader</interfacename>) will treat absolute vs.
      relative paths as you would expect. Relative paths are relative to the
      current working directory, while absolute paths are relative to the root
      of the filesystem.</para>

      <para>For backwards compatibility (historical) reasons however, this
      changes when the <classname>FileSystemApplicationContext</classname> is
      the <literal>ResourceLoader</literal>. The
      <classname>FileSystemApplicationContext</classname> simply forces all
      attached <classname>FileSystemResource</classname> instances to treat
      all location paths as relative, whether they start with a leading slash
      or not. In practice, this means the following are equivalent:</para>

      <programlisting language="java"><![CDATA[ApplicationContext ctx =
    new FileSystemXmlApplicationContext("conf/context.xml");]]></programlisting>

      <programlisting language="java"><![CDATA[ApplicationContext ctx =
    new FileSystemXmlApplicationContext("/conf/context.xml");]]></programlisting>

      <para>As are the following: (Even though it would make sense for them to
      be different, as one case is relative and the other absolute.)</para>

      <programlisting language="java"><![CDATA[FileSystemXmlApplicationContext ctx = ...;
ctx.getResource("some/resource/path/myTemplate.txt");]]></programlisting>

      <programlisting language="java"><![CDATA[FileSystemXmlApplicationContext ctx = ...;
ctx.getResource("/some/resource/path/myTemplate.txt");]]></programlisting>

      <para>In practice, if true absolute filesystem paths are needed, it is
      better to forgo the use of absolute paths with
      <classname>FileSystemResource</classname> /
      <classname>FileSystemXmlApplicationContext</classname>, and just force
      the use of a <classname>UrlResource</classname>, by using the
      <literal>file:</literal> URL prefix.</para>

      <programlisting language="java"><lineannotation>// actual context type doesn't matter, the Resource will always be UrlResource</lineannotation><![CDATA[
ctx.getResource("file:/some/resource/path/myTemplate.txt");]]></programlisting>

      <programlisting language="java"><lineannotation>// force this FileSystemXmlApplicationContext to load its definition via a UrlResource</lineannotation><![CDATA[
ApplicationContext ctx =
    new FileSystemXmlApplicationContext("file:/conf/context.xml");]]></programlisting>
    </section>
  </section>
</chapter>