EndPoint相当于存储过程。0.94.x之前使用EndPoint需要实现CoprocessorProtocol接口，而0.96.x的EndPoint改为用protobufs作为RPC的协议。在此用一个具体的例子说明一下新版的EndPoint该怎么使用。
例如：统计一张表的行数。
首先首先编写protobuf文件并编译。
option java_package = "linecounter";
option java_outer_classname = "LineCounterServer";
option java_generic_services = true;
option java_generate_equals_and_hash = true;
option optimize_for=SPEED;
message CountRequest {
required string askWord = 1;
}
message CountResponse {
required int64 retWord = 1;
}
service LineCounter {
rpc countLine(CountRequest)
returns (CountResponse);
}
编译后会生成LineCounterServer.java
CountRequest是发送给服务端的消息，这里定义字符串askWord来存放具体消息内容。CounterResponse是返回的结果，统计的是行数，所以用long类型存放。LineCounter中定义一个方法countLine，传递请求，返回响应。具体说明请参见protobuf。
实现EndPoint
public class LineCounterEndPoint extends LineCounterServer.LineCounter implements Coprocessor, CoprocessorService {
private RegionCoprocessorEnvironment env;
@Override
public void start(CoprocessorEnvironment coprocessorEnvironment) throws IOException {
if (coprocessorEnvironment instanceof RegionCoprocessorEnvironment)
this.env = (RegionCoprocessorEnvironment) coprocessorEnvironment;
else throw new CoprocessorException("Must be loaded on a table region!!");
}
@Override
public void stop(CoprocessorEnvironment coprocessorEnvironment) throws IOException {
}
@Override
public Service getService() {
return this;
}
@Override
public void countLine(RpcController controller, LineCounterServer.CountRequest request, RpcCallback<LineCounterServer.CountResponse> done) {
RegionScanner scanner = null;
LineCounterServer.CountResponse.Builder respBuilder = LineCounterServer.CountResponse.newBuilder();
if (!"count".equals(request.getAskWord())) {
respBuilder.setRetWord(23333);
} else {
long count = 0;
try {
Scan scan = new Scan();
scan.setMaxVersions(1);
scanner = env.getRegion().getScanner(scan);
List<Cell> list = new ArrayList<>();
while (scanner.next(list))
count += 1;
respBuilder.setRetWord(count);
} catch (IOException e) {
e.printStackTrace();
} finally {
if (scanner != null)
try {
scanner.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
done.run(respBuilder.build());
}
}
LineCounterEndPoint需要继承抽象类LineCounter并实现Coprocessor和CoprocessorService接口。LineCounter在刚才生成的java文件里。
start和stop方法分别负责endpoint执行前的初始化和结束后的清理工作。start方法的参数是一个接口，需要根据实际环境将其转成需要的类型。
主要需要实现的是countLine方法，这也刚才在protobuf中定义的方法。为了测试效果，这里对请求做了一个区分：如果收到的请求信息不是“count”，那么返回23333；否则统计region的记录行数并返回。
实现Client端
public class LineCounterClient {
public static void main(String[] args) throws Throwable {
Configuration conf = HBaseConfiguration.create();
conf.set("hbase.zookeeper.quorum", "zk_host1:2181,zk_host2:2181,zk_host3:2181");
conf.set("hbase.master", "host_master:60000");
HTable table = new HTable(conf, "count_test");
final LineCounterServer.CountRequest req = LineCounterServer.CountRequest.newBuilder().setAskWord("count").build();
Map<byte[], Long> tmpRet = table.coprocessorService(LineCounterServer.LineCounter.class, null, null, new Batch.Call<LineCounterServer.LineCounter, Long>() {
@Override
public Long call(LineCounterServer.LineCounter instance) throws IOException {
ServerRpcController controller = new ServerRpcController();
BlockingRpcCallback<LineCounterServer.CountResponse> rpc = new BlockingRpcCallback<>();
instance.countLine(controller, req, rpc);
LineCounterServer.CountResponse resp = rpc.get();
return resp.getRetWord();
}
});
long ret = 0;
for (long l : tmpRet.values())
ret += l;
System.out.println("lines: " + ret);
}
}
首先设置zookeeper和master的地址和接口信息。然后构造请求即CountRequest，先将请求信息设置为“count”。调用HTable的coprocessorService方法
public <T extends Service, R> Map<byte[],R> coprocessorService(final Class<T> service,
byte[] startKey, byte[] endKey, final Batch.Call<T,R> callable)
该方法有四个参数，第1个参数是protobuf生成的LineCounter类对象。第2个和第3个参数分别为起始和结束rowkey，这里的意思是范围内rowkey所在的region都会调用endpoint，这里设为null表明所有的region都会调用。第4个参数为接口，需要重写call方法。
方法的返回值是Map类型，Map的size与参与计算的region个数一致。所以最后需要做的一步是讲返回结果进行累加，得到最后的结果。
此程序返回5782，是表count_test的行数。若请求消息设置为“hello”，程序返回23333。
coprocessorService还有一个五参数方法，第五个参数是一个CallBack接口，还可以如此实现：
public class LineCounterClient {
public static void main(String[] args) throws Throwable {
Configuration conf = HBaseConfiguration.create();
conf.set("hbase.zookeeper.quorum", "zk_host1:2181,zk_host2:2181,zk_host3:2181");
conf.set("hbase.master", "host_master:60000");
HTable table = new HTable(conf, "count_test");
final LineCounterServer.CountRequest req = LineCounterServer.CountRequest.newBuilder().setAskWord("count").build();
final AtomicLong ret = new AtomicLong();
table.coprocessorService(LineCounterServer.LineCounter.class, null, null, new Batch.Call<LineCounterServer.LineCounter, Long>() {
@Override
public Long call(LineCounterServer.LineCounter instance) throws IOException {
ServerRpcController controller = new ServerRpcController();
BlockingRpcCallback<LineCounterServer.CountResponse> rpc = new BlockingRpcCallback<>();
instance.countLine(controller, req, rpc);
LineCounterServer.CountResponse resp = rpc.get();
return resp.getRetWord();
}
}, new Batch.Callback<Long>() {
@Override
public void update(byte[] region, byte[] row, Long result) {
ret.getAndAdd(result);
System.out.println(Bytes.toString(row)+": "+result);
}
});
System.out.println("lines: " + ret.get());
}
}
每调用一次call方法之后会调用一次update方法，因此在外部定义一个变量ret存放结果，每次调用update时更新ret的值即可。