Erlang and OTP in Action.pdf - Synrc

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NavigableMap that will describe the data to HBase and allow us to access it (annotation #2).
Finally we can get the result out of our navigable map. Getting the actual value of out HBase
is not quite as clear as one would hope. We take the navigable map and call the get method
on it with the name of our field, converting that field to bytes as we do (remember HBase
only understands byte arrays). That gives us another navigable map object that contains the
different values identified by their domain. When we put objects into HBase we specify an
empty domain, so we want to do the same thing when we retrieve them, so we pass in an
empty byte array. This will give us the bytes that make of the value identified by the key
passed in.
The ‘put’ method is much simpler but posses basically the same functionality, just reversed.
public void put(String key, byte[] value) throws IOException {
Put put = new Put(key.getBytes()); #1
put.add("value".getBytes(), "".getBytes(), value); #2
}
_table.put(put); #3
We create a Put Object, specifying the key in the constructor (annotation #1). We then add
the value, in our default empty domain (annotation #2). Notice again that we are only
passing in byte arrays to HBase. Finally, we use the table object that we instantiated in the
constructor of our class to actually insert the value into the system.
Finally we have the delete method. This method is also very similar to the ‘put’ and ‘get’
methods.
public void delete(String key) throws IOException {
Delete del = new Delete(key.getBytes()); #1
}
_table.delete(del); #2
First we create the HBase Delete object (annotation #1), then we pass that to the delet
method of the table object (annotation #2). Once again, we only pass byte arrays to HBase.
Our original goal here was to provide an way to manipulate HBase values from Erlang. In
persuit of that goal we have defined a basic API for interacting with HBase. We now continue
by taking a look at the core part of our system, the SimpleCacheHBaseMain class. This class
provides the core functionality for the Java node that will be providing services to our
system. Code listing 13.2 shows its few member variables and a constructor.
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