How to use Hadoop composite key sorting

When dealing with complex business in Hadoop, it is necessary to use the composite key, which is different from the simple inherited writable interface, but inherits the Writablecomparable<t> interface, in fact, writablecomparable<t The > interface inherits the writable and Comparable<t> interfaces, and if only one class is used as a value-transfer object and not as a key, the writable interface can be inherited.

On the Source:

Public interface writablecomparable<t> extends writable, comparable<t> {}

Public interface Writable {  void write (DataOutput out) throws IOException;  void ReadFields (Datainput in) throws IOException;}

Public interface Comparable<t> {public        int compareTo (T o);}

The following is an example of implementing a composite key, pro-test, available

public class SortKey implements Writablecomparable<sortkey>{private Text name;private intwritable right;public SortKey () {Set (new Text (), New intwritable ());} Public SortKey (Text name, intwritable right) {Set (name, right);} private void Set (Text name,intwritable right) {this.name = Name;this.right = right;} /** * @return The name */public Text getName () {return name;} /** * @param name the name to set */public void SetName (Text name) {this.name = name;} /** * @return The right */public intwritable getRight () {return to right;} /** * @param right to set */public void Setright (intwritable right) {this.right = right;} @Overridepublic void Write (DataOutput out), throws IOException {Name.write (out), Right.write (out);} @Overridepublic void ReadFields (Datainput in) throws IOException {Name.readfields (in); Right.readfields (in);} @Overridepublic int compareTo (SortKey o) {int cmp = Name.compareto (o.name); if (cmp! = 0) {return CMP;} Else{return Right.compareto (O.right);}}

<span style= "White-space:pre" ></span>//so far, you can only use it as a key, but if you need to sort by one of the key values, here's the point.

Static{writablecomparator.define (Sortkey.class, New Comparator ());}  public static class Comparator extends writablecomparator{    private static final text.comparator Text_comparator = new Text.comparator ();p rotected Comparator () {super (sortkey.class);} /* (non-javadoc) * @see Org.apache.hadoop.io.writablecomparator#compare (byte[], int, int, byte[], int, int) */@ overridepublic int Compare (byte[] b1, int s1, int L1, byte[] b2, int s2, int l2) {Try{int firstL1 = Writableutils.decodevi Ntsize (B1[S1]) + Readvint (B1, s1); int firstL2 = Writableutils.decodevintsize (B2[s2]) + readvint (B2, S2);            Return Text_comparator.compare (B1, S1, firstL1, B2, S2, firstL2);} catch (Exception e) {throw new IllegalArgumentException (e);}}}

How to use Hadoop composite key sorting