update doc: add jdbc example for data subscribe

documentation20/webdocs/markdowndocs/advanced features-ch.md

@@ -295,6 +295,142 @@ $ taos
 这时，因为电流超过了10A，您应该可以看到示例程序将它输出到了屏幕上。
 您可以继续插入一些数据观察示例程序的输出。
 
+### jdbc使用数据订阅功能
+
+（1）使用订阅功能前的数据准备
+
+```shell
+# 创建power库
+taos> create database power;
+# 切换库
+taos> use power;
+# 创建超级表
+taos> create table meters(ts timestamp, current float, voltage int, phase int) tags(location binary(64), groupI
+d int);
+# 创建表
+taos> create table d1001 using meters tags ("Beijing.Chaoyang",2);
+taos> create table d1002 using meters tags ("Beijing.Haidian",2);
+# 插入测试数据
+taos> insert into d1001 values("2020-08-15 12:00:00.000", 12, 220, 1),("2020-08-15 12:10:00.000", 12.3, 220, 2),("2020-08-15 12:20:00.000", 12.2, 220, 1);
+taos> insert into d1002 values("2020-08-15 12:00:00.000", 9.9, 220, 1),("2020-08-15 12:10:00.000", 10.3, 220, 1),("2020-08-15 12:20:00.000", 11.2, 220, 1);
+# 从超级表meters查询current大于10的数据
+taos> select * from meters where current > 10;
+      ts       			 		 |      current  |   voltage   |    phase|        location          |   groupid   |
+===========================================================================================================
+ 2020-08-15 12:10:00.000 |    10.30000  |     220      |      1 |      Beijing.Haidian      |           2 |
+ 2020-08-15 12:20:00.000 |    11.20000  |     220      |      1 |      Beijing.Haidian      |           2 |
+ 2020-08-15 12:00:00.000 |    12.00000  |     220      |      1 |      Beijing.Chaoyang     |           2 |
+ 2020-08-15 12:10:00.000 |    12.30000  |     220      |      2 |      Beijing.Chaoyang     |           2 |
+ 2020-08-15 12:20:00.000 |    12.20000  |     220      |      1 |      Beijing.Chaoyang     |           2 |
+Query OK, 5 row(s) in set (0.004896s)
+```
+
+（2）使用jdbc提供的订阅功能
+
+```java
+public class SubscribeDemo {
+    private static final String topic = "topic_meter_current_bg_10";
+    private static final String sql = "select * from meters where current > 10";
+
+    public static void main(String[] args) {
+        Connection connection = null;
+        Statement statement = null;
+        TSDBSubscribe subscribe = null;
+        long subscribeId = 0;
+
+        try {
+            // 加载驱动
+            Class.forName("com.taosdata.jdbc.TSDBDriver");
+            // 获取Connectin
+            Properties properties = new Properties();
+            properties.setProperty(TSDBDriver.PROPERTY_KEY_CHARSET, "UTF-8");
+            properties.setProperty(TSDBDriver.PROPERTY_KEY_TIME_ZONE, "UTC-8");
+            String jdbcUrl = "jdbc:TAOS://127.0.0.1:6030/power?user=root&password=taosdata";
+            connection = DriverManager.getConnection(jdbcUrl, properties);
+            System.out.println("create the connection");
+            // 创建Subscribe
+            subscribe = ((TSDBConnection) connection).createSubscribe();
+            // subscribe订阅topic，topic为主题名称，sql为查询语句，restart代表是否每次订阅接受历史数据
+            subscribeId = subscribe.subscribe(topic, sql, true);
+            System.out.println("create a subscribe topic: " + topic + "@[" + subscribeId + "]");
+            int count = 0;
+            while (true) {
+                // 消费数据
+                TSDBResultSet resultSet = subscribe.consume(subscribeId);
+                // 打印结果集
+                if (resultSet != null) {
+                    ResultSetMetaData metaData = resultSet.getMetaData();
+                    while (resultSet.next()) {
+                        int columnCount = metaData.getColumnCount();
+                        for (int i = 1; i <= columnCount; i++) {
+                            System.out.print(metaData.getColumnLabel(i) + " : " + resultSet.getString(i) + "\t");
+                        }
+                        System.out.println("\n====================");
+                        count++;
+                    }
+                }
+                if (count > 10)
+                    break;
+                TimeUnit.SECONDS.sleep(1);
+            }
+        } catch (Exception e) {
+            e.printStackTrace();
+        } finally {
+            try {
+                if (null != subscribe && subscribeId != 0) {
+                    subscribe.unsubscribe(subscribeId, true);
+                    System.out.println("unsubscribe the top@[" + subscribeId + "]");
+                }
+                if (statement != null) {
+                    statement.close();
+                    System.out.println("close the statement.");
+                }
+                if (connection != null) {
+                    connection.close();
+                    System.out.println("close the connection.");
+                }
+            } catch (SQLException throwables) {
+                throwables.printStackTrace();
+            }
+        }
+    }
+}
+```
+
+（3）订阅功能演示
+
+运行demo，首先，subscribe会将满足情况的历史数据消费
+
+```shell
+# java -jar subscribe.jar 
+
+ts : 1597464000000	current : 12.0	voltage : 220	phase : 1	location : Beijing.Chaoyang	groupid : 2	
+====================
+ts : 1597464600000	current : 12.3	voltage : 220	phase : 2	location : Beijing.Chaoyang	groupid : 2	
+====================
+ts : 1597465200000	current : 12.2	voltage : 220	phase : 1	location : Beijing.Chaoyang	groupid : 2	
+====================
+ts : 1597464600000	current : 10.3	voltage : 220	phase : 1	location : Beijing.Haidian	groupid : 2	
+====================
+ts : 1597465200000	current : 11.2	voltage : 220	phase : 1	location : Beijing.Haidian	groupid : 2	
+====================
+```
+
+接着，使用taos客户端向表中新增数据
+
+```shell
+# taos
+taos> use power；
+taos> insert into d1001 values("2020-08-15 12:40:00.000", 12.4, 220, 1);
+```
+
+查看数据消费情况
+
+```shell
+ts : 1597466400000	current : 12.4	voltage : 220	phase : 1	location : Beijing.Chaoyang	groupid : 2	
+====================
+```
+
 
 ## 缓存(Cache)