[hbase]使用HBase的Java api查询HBase

查询操作，不管是关系型数据库，还是非关系型数据库，相对于增删改，都占了很大的比重。

查询不易，且行且珍惜。

使用HBase的java api来进行查询，主要有两种方式，一种是直接通过rowkey（类似于主键）来查询；另一种是scan，扫描表（扫描某一列族，扫描某一colume，以rowkey的开始和结束做为一个范围进行扫描）
1、通过rowkey来查询一条记录

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//根据rowkey查询一条记录 public void queryByRowKey(Configuration conf,String tableName,String rowKey){     HTable hTable = null;     try {         hTable = new HTable(conf, tableName);         Get get = new Get( rowKey.getBytes());         Result result = hTable.get(get);         System.err.println("rowkey为:" + rowKey);         HashMap<String, String> hm = new HashMap<String, String>();         for (KeyValue kv: result.raw()) {             hm.put(new String(kv.getFamily()) , new String(kv.getValue()));             System.err.println("rowkey:" + new String(kv.getKey()));             System.err.println("-------------------------------");             System.err.println("columnFamily:" + new String(kv.getFamily()) +"===column:" + new String(kv.getQualifier()) + "===getValue:" + new String(kv.getValue()));         }         System.err.println(hm.size());         System.err.println(hm.toString());     } catch (IOException e) {         e.printStackTrace();     }finally {         try {             hTable.close();         } catch (IOException e) {             e.printStackTrace();         }     } }

2、扫描整个表

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//扫描hbase表，获取所有记录 public void getAllRow(Configuration conf, String tableName){     HTable hTable = null;     ResultScanner rs = null;     try {         hTable = new HTable(conf, "DANIU");         rs = hTable.getScanner(new Scan());         //循环rowkey         for (Result result : rs) {             for (KeyValue kv : result.raw()) {                 System.err.println("rowkey:" + new String(kv.getKey()));                 System.err.println("-------------------------------");                 System.err.println("columnFamily:" + new String(kv.getFamily()) +"===column:" +new String(kv.getQualifier()) + "===getValue:" + new String(kv.getValue()));             }         }     } catch (IOException e) {         e.printStackTrace();     } finally{         rs.close();         try {             hTable.close();         } catch (IOException e) {             e.printStackTrace();         }     } }

3、根据一个条件，扫描。使用一个filter

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//根据查询多条记录，一个filter的使用 public void filterSingleColumnValueFilter(Configuration conf,String tableName){     HTable hTable = null;     ResultScanner rs = null;     try {         hTable = new HTable(conf, tableName);         Filter filter = new SingleColumnValueFilter("columnfamily1".getBytes(), null, CompareOp.EQUAL, "value1".getBytes());         Scan scan = new Scan();         scan.setFilter(filter);         rs = hTable.getScanner(scan);         for (Result result : rs) {             for (KeyValue kv : result.raw()) {                 System.err.println("rowkey:" + new String(kv.getKey()));                 System.err.println("-------------------------------");                 System.err.println("columnFamily:" + new String(kv.getFamily()) +"===column:" +new String(kv.getQualifier()) + "===getValue:" + new String(kv.getValue()));             }         }     } catch (IOException e) {         e.printStackTrace();     }finally{         rs.close();         try {             hTable.close();         } catch (IOException e) {             e.printStackTrace();         }     } }

4、使用多个条件来查询数据。多个filter的使用。

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//更多条件，查询更多数据，多个filter的使用。 public void filterMore(Configuration conf,String tableName){     HTable hTable = null;     ResultScanner rs = null;     try {         hTable = new HTable(conf, tableName);         List<Filter> filters = new ArrayList<Filter>();                   Filter filter1 = new SingleColumnValueFilter("columnfamily1".getBytes(), null, CompareOp.EQUAL, "value1".getBytes());         filters.add(filter1);                   Filter filter2 = new SingleColumnValueFilter("columnfamily2".getBytes(), null, CompareOp.EQUAL, "value2".getBytes());         filters.add(filter2);                   //还可以添加更多的filter         Scan scan = new Scan();         rs = hTable.getScanner(scan);         for (Result result : rs) {             for (KeyValue kv : result.raw()) {                 System.err.println("rowkey:" + new String(kv.getKey()));                 System.err.println("-------------------------------");                 System.err.println("columnFamily:" + new String(kv.getFamily()) +"===column:" +new String(kv.getQualifier()) + "===getValue:" + new String(kv.getValue()));             }         }     } catch (IOException e) {         e.printStackTrace();     }finally{         rs.close();         try {             hTable.close();         } catch (IOException e) {             e.printStackTrace();         }     } }