关于表

• Overview
• Example API Usage

Put, Get 和 Delete这些操作在执行期间会对行进行加锁. 而在单行上的并发修改会被序列化执行. 在没有行锁的制约时,Get and scan可并行运行，并且保证不返回包含未完全写入的数据.

通过ZooKeeper，客户端代码可访问某个集群信息. 这意味着必须在客户端上的CLASSPATH设置了ZooKeeper的代理配置，才能正常使用. 这通常也是说要保证客户端能找到hbase-site.xml文件.

用法用例

当你拥有一个正在运行的HBase服务, 你可能回想在上面运行你的一个应用. 如果你的程序是用Java构建的,那么就应该使用Java API来进行对HBase的操作. 以下是一个简单的操作HBase示例. 该示例假定已创建了一个名为"myTable"的表，其列族名为"myColumnFamily".

import java.io.IOException;import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.client.Get;
import org.apache.hadoop.hbase.client.HTable;
import org.apache.hadoop.hbase.client.Put;
import org.apache.hadoop.hbase.client.Result;
import org.apache.hadoop.hbase.client.ResultScanner;
import org.apache.hadoop.hbase.client.Scan;
import org.apache.hadoop.hbase.util.Bytes;// Class that has nothing but a main.
// Does a Put, Get and a Scan against an hbase table.
public class MyLittleHBaseClient {public static void main(String[] args) throws IOException {// You need a configuration object to tell the client where to connect.// When you create a HBaseConfiguration, it reads in whatever you've set// into your hbase-site.xml and in hbase-default.xml, as long as these can// be found on the CLASSPATHConfiguration config = HBaseConfiguration.create();// This instantiates an HTable object that connects you to// the "myLittleHBaseTable" table.HTable table = new HTable(config, "myLittleHBaseTable");// To add to a row, use Put.  A Put constructor takes the name of the row// you want to insert into as a byte array.  In HBase, the Bytes class has// utility for converting all kinds of java types to byte arrays.  In the// below, we are converting the String "myLittleRow" into a byte array to// use as a row key for our update. Once you have a Put instance, you can// adorn it by setting the names of columns you want to update on the row,// the timestamp to use in your update, etc.If no timestamp, the server// applies current time to the edits.Put p = new Put(Bytes.toBytes("myLittleRow"));// To set the value you'd like to update in the row 'myLittleRow', specify// the column family, column qualifier, and value of the table cell you'd// like to update.  The column family must already exist in your table// schema.  The qualifier can be anything.  All must be specified as byte// arrays as hbase is all about byte arrays.  Lets pretend the table// 'myLittleHBaseTable' was created with a family 'myLittleFamily'.p.add(Bytes.toBytes("myLittleFamily"), Bytes.toBytes("someQualifier"),Bytes.toBytes("Some Value"));// Once you've adorned your Put instance with all the updates you want to// make, to commit it do the following (The HTable#put method takes the// Put instance you've been building and pushes the changes you made into// hbase)table.put(p);// Now, to retrieve the data we just wrote. The values that come back are// Result instances. Generally, a Result is an object that will package up// the hbase return into the form you find most palatable.Get g = new Get(Bytes.toBytes("myLittleRow"));Result r = table.get(g);byte [] value = r.getValue(Bytes.toBytes("myLittleFamily"),Bytes.toBytes("someQualifier"));// If we convert the value bytes, we should get back 'Some Value', the// value we inserted at this location.String valueStr = Bytes.toString(value);System.out.println("GET: " + valueStr);// Sometimes, you won't know the row you're looking for. In this case, you// use a Scanner. This will give you cursor-like interface to the contents// of the table.  To set up a Scanner, do like you did above making a Put// and a Get, create a Scan.  Adorn it with column names, etc.Scan s = new Scan();s.addColumn(Bytes.toBytes("myLittleFamily"), Bytes.toBytes("someQualifier"));ResultScanner scanner = table.getScanner(s);try {// Scanners return Result instances.// Now, for the actual iteration. One way is to use a while loop like so:for (Result rr = scanner.next(); rr != null; rr = scanner.next()) {// print out the row we found and the columns we were looking forSystem.out.println("Found row: " + rr);}// The other approach is to use a foreach loop. Scanners are iterable!// for (Result rr : scanner) {//   System.out.println("Found row: " + rr);// }} finally {// Make sure you close your scanners when you are done!// Thats why we have it inside a try/finally clausescanner.close();}}
}

原文链接：http://hbase.apache.org/apidocs/org/apache/hadoop/hbase/client/package-summary.html