[TD-2541]<fix>: optimized the connection pool demo codes

tests/examples/JDBC/connectionPools/src/main/java/com/taosdata/demo/ConnectionPoolDemo.java

 package com.taosdata.demo;
 
-import com.taosdata.demo.common.InsertTask;
 import com.taosdata.demo.pool.C3p0Builder;
 import com.taosdata.demo.pool.DbcpBuilder;
 import com.taosdata.demo.pool.DruidPoolBuilder;
@@ -11,9 +10,6 @@ import javax.sql.DataSource;
 import java.sql.Connection;
 import java.sql.SQLException;
 import java.sql.Statement;
-import java.util.concurrent.ExecutorService;
-import java.util.concurrent.Executors;
-import java.util.concurrent.TimeUnit;
 
 public class ConnectionPoolDemo {
 
@@ -96,13 +92,13 @@ public class ConnectionPoolDemo {
             e.printStackTrace();
         }
 
-
 //        ExecutorService executor = Executors.newFixedThreadPool(threadCount);
 //        while (true) {
 //            executor.execute(new InsertTask(dataSource, dbName, tableSize, batchSize));
 //            if (sleep > 0)
 //                TimeUnit.MILLISECONDS.sleep(sleep);
 //        }
+
     }
 
     private static void init(DataSource dataSource) {

tests/examples/JDBC/connectionPools/src/main/java/com/taosdata/demo/pool/DruidPoolBuilder.java

 package com.taosdata.demo.pool;
 
 import com.alibaba.druid.pool.DruidDataSource;
+import com.alibaba.druid.pool.DruidDataSourceFactory;
 
 import javax.sql.DataSource;
+import java.util.Properties;
 
 public class DruidPoolBuilder {
 
-    public static DataSource getDataSource(String host, int poolSize) {
+    public static DataSource getDataSource(String host, int poolSize) throws Exception {
         final String url = "jdbc:TAOS://" + host + ":6030";
 
         DruidDataSource dataSource = new DruidDataSource();
         // jdbc properties
-        dataSource.setUrl(url);
         dataSource.setDriverClassName("com.taosdata.jdbc.TSDBDriver");
+        dataSource.setUrl(url);
         dataSource.setUsername("root");
         dataSource.setPassword("taosdata");
-
         // pool configurations
-        dataSource.setInitialSize(poolSize);//初始连接数，默认0
-        dataSource.setMinIdle(poolSize);//最小闲置数
-        dataSource.setMaxActive(poolSize);//最大连接数，默认8
-        dataSource.setMaxWait(30000);//获取连接的最大等待时间，单位毫秒
+        dataSource.setInitialSize(10);
+        dataSource.setMinIdle(10);
+        dataSource.setMaxActive(10);
+        dataSource.setMaxWait(30000);
         dataSource.setValidationQuery("select server_status()");
         return dataSource;
     }
 
-
 }

tests/examples/JDBC/connectionPools/src/main/java/com/taosdata/demo/pool/HikariCpBuilder.java

@@ -18,6 +18,7 @@ public class HikariCpBuilder {
         config.setMinimumIdle(3);           //minimum number of idle connection
         config.setMaximumPoolSize(10);      //maximum number of connection in the pool
         config.setConnectionTimeout(30000); //maximum wait milliseconds for get connection from pool
+        config.setMaxLifetime(0);       // maximum life time for each connection
         config.setIdleTimeout(0);       // max idle time for recycle idle connection
         config.setConnectionTestQuery("select server_status()"); //validation query