[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();
}
}
}
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