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From lewi...@apache.org
Subject svn commit: r1663401 - /gora/site/trunk/content/current/gora-shims.md
Date Mon, 02 Mar 2015 19:23:56 GMT
Author: lewismc
Date: Mon Mar  2 19:23:56 2015
New Revision: 1663401

URL: http://svn.apache.org/r1663401
Log:
GORA-384 Provide documentation on Gora Shims layer

Modified:
    gora/site/trunk/content/current/gora-shims.md

Modified: gora/site/trunk/content/current/gora-shims.md
URL: http://svn.apache.org/viewvc/gora/site/trunk/content/current/gora-shims.md?rev=1663401&r1=1663400&r2=1663401&view=diff
==============================================================================
--- gora/site/trunk/content/current/gora-shims.md (original)
+++ gora/site/trunk/content/current/gora-shims.md Mon Mar  2 19:23:56 2015
@@ -40,34 +40,116 @@ should be used as below.**
 
 [Click Here](http://search.maven.org/#artifactdetails|org.apache.gora|gora-shims-distribution|0.6|bundle)
 
-##Direct Dependency
-
 #gora-shims-hadoop
 
 ##Description
 
+This module contains functional Java code for enabling dynamic selection of the Hadoop environment
based upon the 
+presence of **org.apache.hadoop.util.VersionInfo**. This is a two-part process where we first
obtain the [Hadoop
+Major version](https://github.com/apache/gora/blob/master/gora-shims-hadoop/src/main/java/org/apache/gora/shims/hadoop/HadoopShimFactory.java#L79-L94).
+We then [select the appropriate Gora Shim](https://github.com/apache/gora/blob/master/gora-shims-hadoop/src/main/java/org/apache/gora/shims/hadoop/HadoopShimFactory.java#L56-L77)

+based on detecting the Hadoop Major version. This code looks the following:
+
+
+    /**
+     * Get the Hadoop major version number.
+     *
+     * @return The major version number of Hadoop.
+     */
+    public String getMajorVersion() {
+      String vers = VersionInfo.getVersion();
+      String[] parts = vers.split("\\.");
+      if (parts.length < 2) {
+        throw new RuntimeException("Unable to parse Hadoop version: "
+        + vers + " (expected X.Y.* format)");
+      }
+      return parts[0];
+    }
+
+    /**
+     * Get the Hadoop shim for the Hadoop version on the class path. In case it
+     * fails to obtain an appropriate shim (i.e. unsupported Hadoop version), it
+     * throws a {@link RuntimeException}.
+     *
+     * Note that this method is potentially costly.
+     *
+     * @return A newly created instance of a {@link HadoopShim}.
+     */
+    public HadoopShim getHadoopShim() {
+      String version = getMajorVersion();
+      String className = HADOOP_VERSION_TO_IMPL_MAP.get(version);
+      try {
+        Class<?> class1 = Class.forName(className);
+        return HadoopShim.class.cast(class1.newInstance());
+      } catch (Exception e) {
+        throw new RuntimeException(
+          "Could not load Hadoop shim for version " + version
+          + ", className=" + className, e);
+      }
+    }
 
-##Dependency
-
+##Dependency Definition
 
-##Direct Dependency
+[Click Here](http://search.maven.org/#artifactdetails|org.apache.gora|gora-shims-hadoop|0.6|bundle)
 
 #gora-shims-hadoop1
 
 ##Description
 
+This module provides all functionality for Hadoop 1.X support in Gora. The Hadoop version
is specified within
+the project [pom.xml](https://github.com/apache/gora/blob/master/pom.xml) within the **${hadoop1-version}**
variable.
+
+The actual [code implementation](https://github.com/apache/gora/blob/master/gora-shims-hadoop1/src/main/java/org/apache/gora/shims/hadoop1/HadoopShim1.java)

+is very simple. Essentially it consists of two Java methods
+
+     /**
+      * {@inheritDoc}
+      */
+     public Job createJob(Configuration configuration) throws IOException {
+       return new Job(configuration);
+     }
+     /**
+      * {@inheritDoc}
+      */
+     public JobContext createJobContext(Configuration configuration) {
+       return new JobContext(configuration, null); 
+     }
 
-##Dependency
 
+##Dependency Definition
+
+[Click Here](http://search.maven.org/#artifactdetails|org.apache.gora|gora-shims-hadoop1|0.6|bundle)
 
-##Direct Dependency
 
 #gora-shims-hadoop2
 
 ##Description
 
 
-##Dependency
+This module provides all functionality for Hadoop 2.X support in Gora. The Hadoop version
is specified within
+the project [pom.xml](https://github.com/apache/gora/blob/master/pom.xml) within the **${hadoop2-version}**
variable.
+
+The actual [code implementation](https://github.com/apache/gora/blob/master/gora-shims-hadoop1/src/main/java/org/apache/gora/shims/hadoop1/HadoopShim1.java)

+is very simple. Essentially it consists of two Java methods
+    /**
+     * {@inheritDoc}
+     *
+     * Use the Hadoop 2.x way of creating a {@link Job} object.
+     */
+    public Job createJob(Configuration configuration) throws IOException {
+      Job instance = Job.getInstance(configuration);
+      return instance;
+    }
+    /**
+     * {@inheritDoc}
+     *
+     * Use the Hadoop 2.x way of creating a {@link JobContext} object.
+     */
+    public JobContext createJobContext(Configuration configuration) {
+      return new JobContextImpl(configuration, null);
+    }
+
+##Dependency Definition
 
+[Click Here](http://search.maven.org/#artifactdetails|org.apache.gora|gora-shims-hadoop2|0.6|bundle)
 
-##Direct Dependency



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