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法學如何在JDBC的CachedRowSet中檢查列名是否存在？
CachedRowSet介面沒有提供任何方法來確定特定列是否存在。
因此，要查詢**RowSet**是否包含特定列，需要將RowSet中每一列的名稱與所需名稱進行比較。為此，需要：
- 使用**getMetaData()**方法從RowSet檢索**ResultSetMetaData**物件。
ResultSetMetaData meta = rowSet.getMetaData();
- 使用**getColumnCount()**方法獲取**RowSet**中的列數。
int columnCount = meta.getColumnCount();
- **getColumnName()**方法返回指定索引的列名。使用此方法從索引1到列數檢索RowSet的列名，並將每一列的名稱與所需的列名進行比較。
boolean flag = false;
for (int i = 1; i <=columnCount; i++) {
if(meta.getColumnName(i).equals("ProductName")) {
flag = true;
}
}示例
讓我們在MySQL資料庫中建立一個名為**sales**的表，其中一列為自動遞增列，使用如下所示的CREATE語句：
CREATE TABLE Sales( ID INT PRIMARY KEY AUTO_INCREMENT, ProductName VARCHAR (20), CustomerName VARCHAR (20), DispatchDate date, DeliveryTime time, Price INT, Location VARCHAR(20) );
現在，我們將使用INSERT語句在**sales**表中插入5條記錄：
insert into sales (ProductName, CustomerName, DispatchDate, DeliveryTime, Price, Location) values('Key-Board', 'Raja', DATE('2019-09-01'), TIME('11:00:00'), 7000, 'India');
insert into sales (ProductName, CustomerName, DispatchDate, DeliveryTime, Price, Location) values('Earphones', 'Roja', DATE('2019-05-01'), TIME('11:00:00'), 2000, 'Vishakhapatnam');
insert into sales (ProductName, CustomerName, DispatchDate, DeliveryTime, Price, Location) values('Mouse', 'Puja', DATE('2019-03-01'), TIME('10:59:59'), 3000, 'Vijayawada');
insert into sales (ProductName, CustomerName, DispatchDate, DeliveryTime, Price, Location) values('Mobile', 'Vanaja', DATE('2019-03-01'), TIME('10:10:52'), 9000, 'Chennai');
insert into sales (ProductName, CustomerName, DispatchDate, DeliveryTime, Price, Location) values('Headset', 'Jalaja', DATE('2019-04-06'), TIME('11:08:59'), 6000, 'Goa');下面的JDBC程式建立與資料庫的連線，將Sales表的內容檢索到**RowSet**中，並找出它是否包含名為ProductName的列。
示例
import java.sql.DriverManager;
import java.sql.ResultSetMetaData;
import javax.sql.rowset.CachedRowSet;
import javax.sql.rowset.RowSetFactory;
import javax.sql.rowset.RowSetProvider;
public class CachedRowSetExample {
public static void main(String args[]) throws Exception {
//Registering the Driver
DriverManager.registerDriver(new com.mysql.jdbc.Driver());
//Creating the RowSet object
RowSetFactory factory = RowSetProvider.newFactory();
CachedRowSet rowSet = factory.createCachedRowSet();
//Setting the URL
String mysqlUrl = "jdbc:mysql:///SampleDB";
rowSet.setUrl(mysqlUrl);
//Setting the user name
rowSet.setUsername("root");
//Setting the password
rowSet.setPassword("password");
//Setting the query/command
rowSet.setCommand("select * from Sales");
//Executing the command
rowSet.execute();
//Retrieving the ResultSetMetaData object
ResultSetMetaData meta = rowSet.getMetaData();
int columnCount = meta.getColumnCount();
boolean flag = false;
for (int i = 1; i <=columnCount; i++) {
if(meta.getColumnName(i).equals("ProductName")){
flag = true;
}
}
if(flag) {
System.out.println("Specified column exist");
} else {
System.out.println("Specified column does not exists");
}
System.out.println("Contents of the row set");
while(rowSet.next()) {
System.out.print("ID: "+rowSet.getInt("ID")+", ");
System.out.print("Product Name: "+rowSet.getString("ProductName")+", ");
System.out.print("Customer Name: "+rowSet.getString("CustomerName")+", ");
System.out.print("Dispatch Date: "+rowSet.getDate("DispatchDate")+", ");
System.out.print("Delivery Time: "+rowSet.getTime("DeliveryTime")+", "););
System.out.print("Price: "+rowSet.getString("Price")+", ");
System.out.print("Location: "+rowSet.getString("Location"));
System.out.println("");
}
}
}輸出
Specified column exists Contents of the row set ID: 1, Product Name: Key-Board, Customer Name: Raja, Dispatch Date: 2019-09-01, Delivery Time: 05:30:00, Price: 2000, Location: Hyderabad ID: 2, Product Name: Earphones, Customer Name: Roja, Dispatch Date: 2019-05-01, Delivery Time: 05:30:00, Price: 2000, Location: Vishakhapatnam ID: 3, Product Name: Mouse, Customer Name: Puja, Dispatch Date: 2019-03-01, Delivery Time: 05:29:59, Price: 3000, Location: Vijayawada ID: 4, Product Name: Mobile, Customer Name: Vanaja, Dispatch Date: 2019-03-01, Delivery Time: 04:40:52, Price: 9000, Location: Chennai ID: 5, Product Name: Headset, Customer Name: Jalaja, Dispatch Date: 2019-04-06, Delivery Time: 18:38:59, Price: 6000, Location: Goa
更新於：2019年7月30日
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