标签：des style blog http color os io 使用 java
1.连接
HBaseConfiguration conf = HBaseConfiguration.create(); HTable table1 = new HTable(conf, "myTable"); HTable table2 = new HTable(conf, "myTable");
而不是这样的代码：
HBaseConfiguration conf1 = HBaseConfiguration.create(); HTable table1 = new HTable(conf1, "myTable"); HBaseConfiguration conf2 = HBaseConfiguration.create(); HTable table2 = new HTable(conf2, "myTable");
2.连接池
当面对多线程访问需求时，我们可以预先建立HConnection，参见以下代码：
Example 9.1. Pre-Creating a HConnection // Create a connection to the cluster. HConnection connection = HConnectionManager.createConnection(Configuration); HTableInterface table = connection.getTable("myTable"); // use table as needed, the table returned is lightweight table.close(); // use the connection for other access to the cluster connection.close();
构建HTableInterface实现是非常轻量级的，并且资源是可控的。
HConnection connection = HConnectionManager.createConnection(config); HTableInterface table = connection.getTable("tablename"); try { // Use the table as needed, for a single operation and a single thread } finally { table.close(); connection.close(); }
package com.bigdata.dbhbase096; import java.io.IOException; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.hbase.Cell; import org.apache.hadoop.hbase.CellUtil; import org.apache.hadoop.hbase.HBaseConfiguration; import org.apache.hadoop.hbase.client.HConnection; import org.apache.hadoop.hbase.client.HConnectionManager; import org.apache.hadoop.hbase.client.HTableInterface; 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; public class ConnectionPoolTest { private static final String QUORUM = "compute1"; private static final String CLIENTPORT = "2181"; private static final String TABLENAME = "minifiletable4"; private static Configuration conf = null; private static HConnection conn = null; static{ try { conf = HBaseConfiguration.create(); conf.set("hbase.zookeeper.quorum", QUORUM); conf.set("hbase.zookeeper.property.clientPort", CLIENTPORT); conn = HConnectionManager.createConnection(conf); } catch (IOException e) { e.printStackTrace(); } } public static void main(String[] args) throws IOException { HTableInterface htable = ConnectionPoolTest.conn.getTable(TABLENAME); try { Scan scan = new Scan(); ResultScanner rs = htable.getScanner(scan); for (Result r : rs.next(5)) { for (Cell cell : r.rawCells()) { System.out.println("Rowkey : " + Bytes.toString(r.getRow()) + " Familiy:Quilifier : " + Bytes.toString(CellUtil.cloneQualifier(cell)) + " Value : " + Bytes.toString(CellUtil.cloneValue(cell)) + " Time : " + cell.getTimestamp()); } } } finally { htable.close(); } } }
/** * Get the connection that goes with the passed <code>conf</code> configuration instance. * If no current connection exists, method creates a new connection and keys it using * connection-specific properties from the passed {@link Configuration}; see * {@link HConnectionKey}. * @param conf configuration * @return HConnection object for <code>conf</code> * @throws ZooKeeperConnectionException */ @Deprecated public static HConnection getConnection(final Configuration conf) throws IOException { HConnectionKey connectionKey = new HConnectionKey(conf); synchronized (CONNECTION_INSTANCES) { HConnectionImplementation connection = CONNECTION_INSTANCES.get(connectionKey); if (connection == null) { connection = (HConnectionImplementation)createConnection(conf, true); CONNECTION_INSTANCES.put(connectionKey, connection); } else if (connection.isClosed()) { HConnectionManager.deleteConnection(connectionKey, true); connection = (HConnectionImplementation)createConnection(conf, true); CONNECTION_INSTANCES.put(connectionKey, connection); } connection.incCount(); return connection; } }
根据传入的conf构建HConnectionKey，然后以HConnectionKey实例为key到连接池Map对象CONNECTION_INSTANCES中去查找connection，如果找到就返回connection，如果找不到就新建，如果找到但已被关闭，就删除再新建。
我们来看HConnectionKey的构造函数：
HConnectionKey(Configuration conf) { Map<String, String> m = new HashMap<String, String>(); if (conf != null) { for (String property : CONNECTION_PROPERTIES) { String value = conf.get(property); if (value != null) { m.put(property, value); } } } this.properties = Collections.unmodifiableMap(m); try { UserProvider provider = UserProvider.instantiate(conf); User currentUser = provider.getCurrent(); if (currentUser != null) { username = currentUser.getName(); } } catch (IOException ioe) { HConnectionManager.LOG.warn("Error obtaining current user, skipping username in HConnectionKey", ioe); } }
由以上源码可知，接收conf构造HConnectionKey实例时，其实是将conf配置文件中的属性赋值给HConnectionKey自身的属性，换句话说，不管你new几次，只要conf的属性相同，new出来的HConnectionKey实例的属性都相同。
结论一：conf的属性 --》 HConnectionKey实例的属性
接下来，回到getConnection源码中看到这样一句话：
HConnectionImplementation connection = CONNECTION_INSTANCES.get(connectionKey);
该代码是以HConnectionKey实例为key来查找CONNECTION_INSTANCES这个LinkedHashMap中是否已经包含了HConnectionKey实例为key的键值对，这里要注意的是，map的get方法，其实获取的是key的hashcode，这个自己读JDK源码就能看到。
而HConnectionKey已经重载了hashcode方法：
@Override public int hashCode() { final int prime = 31; int result = 1; if (username != null) { result = username.hashCode(); } for (String property : CONNECTION_PROPERTIES) { String value = properties.get(property); if (value != null) { result = prime * result + value.hashCode(); } } return result; }
在该代码中，最终返回的hashcode取决于当前用户名及当前conf配置文件的属性。所以，只要conf配置文件的属性和用户相同，HConnectionKey实例的hashcode就相同！
结论二：conf的属性 --》HConnectionKey实例的hashcode
Example 9.1. Pre-Creating a HConnection
// Create a connection to the cluster.
HConnection connection = HConnectionManager.createConnection(Configuration);
HTableInterface table = connection.getTable("myTable");
// use table as needed, the table returned is lightweight
table.close();
// use the connection for other access to the cluster
connection.close();
/** * Get the connection that goes with the passed <code>conf</code> configuration instance. * If no current connection exists, method creates a new connection and keys it using * connection-specific properties from the passed {@link Configuration}; see * {@link HConnectionKey}. * @param conf configuration * @return HConnection object for <code>conf</code> * @throws ZooKeeperConnectionException */ public static HConnection getConnection(final Configuration conf) throws IOException { return ConnectionManager.getConnectionInternal(conf); }
这个不是重点，重点是最新版本代码的pom：
<groupId>org.apache.hbase</groupId> 40 <artifactId>hbase</artifactId> <packaging>pom</packaging> <version>2.0.0-SNAPSHOT</version> <name>HBase</name> <description> Apache HBase\99 is the Hadoop database. Use it when you need random, realtime read/write access to your Big Data. This project‘s goal is the hosting of very large tables -- billions of rows X millions of columns -- atop clusters of commodity hardware. </description>
Hbase的连接池--HTablePool被Deprecated之后
标签：des style blog http color os io 使用 java
原文地址：http://www.cnblogs.com/joqk/p/3956167.html
