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法学如何使用JDBC API从数据库现有表中检索记录？
A. 你可以使用SELECT查询读取/获取表中记录的内容。这将以结果表的形式返回数据，这些结果表称为结果集。
语法
SELECT column1, column2, columnN FROM table_name; Or, SELECT * FROM table_name;
要使用JDBC API检索表中某一行的内容，你需要：
注册驱动程序：使用**DriverManager**类的**registerDriver()**方法注册驱动程序类。将驱动程序类名作为参数传递给它。
建立连接：使用**DriverManager**类的**getConnection()**方法连接到数据库。将URL（字符串）、用户名（字符串）、密码（字符串）作为参数传递给它。
创建语句：使用**Connection**接口的**createStatement()**方法创建一个Statement对象。
执行查询：使用Statement接口的executeQuery()方法执行查询。
示例
假设我们在MySQL数据库中有一个名为mydatabase的数据库，其中包含一个名为customers的表，其中有12条记录，如下所示：
+----+-----------+------+---------+----------------+ | ID | NAME | AGE | SALARY | ADDRESS | +----+-----------+------+---------+----------------+ | 1 | Amit | 25 | 3000.00 | Hyderabad | | 2 | Kalyan | 27 | 4000.00 | Vishakhapatnam | | 3 | Renuka | 30 | 5000.00 | Delhi | | 4 | Archana | 24 | 1500.00 | Mumbai | | 5 | Koushik | 30 | 9000.00 | Kota | | 6 | Hardik | 45 | 6400.00 | Bhopal | | 7 | Trupthi | 33 | 4360.00 | Ahmedabad | | 8 | Mithili | 26 | 4100.00 | Vijayawada | | 9 | Maneesh | 39 | 4000.00 | Hyderabad | | 10 | Rajaneesh | 30 | 6400.00 | Delhi | | 11 | Komal | 29 | 8000.00 | Ahmedabad | | 12 | Manyata | 25 | 5000.00 | Vijayawada | +----+-----------+------+---------+----------------+
下面的JDBC程序建立与MySQL的连接，检索customers表中的所有记录并显示它们。
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class ReadRecordsExample {
public static void main(String args[]) throws SQLException {
//Registering the Driver
DriverManager.registerDriver(new com.mysql.jdbc.Driver());
//Getting the connection
String mysqlUrl = "jdbc:mysql:///mydatabase";
Connection con = DriverManager.getConnection(mysqlUrl, "root", "password");
System.out.println("Connection established......");
//Creating the Statement
Statement stmt = con.createStatement();
//Query to retrieve records
String query = "Select * from Customers";
//Executing the query
ResultSet rs = stmt.executeQuery(query);
System.out.println("Contents of the Customers table:");
while(rs.next()) {
System.out.print("ID: "+rs.getInt("ID")+", ");
System.out.print("Name: "+rs.getString("Name")+", ");
System.out.print("Age: "+rs.getInt("Age")+", ");
System.out.print("Salary: "+rs.getInt("Salary")+", ");
System.out.print("Address: "+rs.getString("Address"));
System.out.println();
}
}
}输出
Connection established...... Contents of the Customers table: ID: 1, Name: Amit, Age: 25, Salary: 3000, Address: Hyderabad ID: 2, Name: Kalyan, Age: 27, Salary: 4000, Address: Vishakhapatnam ID: 3, Name: Renuka, Age: 30, Salary: 5000, Address: Delhi ID: 4, Name: Archana, Age: 24, Salary: 1500, Address: Mumbai ID: 5, Name: Koushik, Age: 30, Salary: 9000, Address: Kota ID: 6, Name: Hardik, Age: 45, Salary: 6400, Address: Bhopal ID: 7, Name: Trupthi, Age: 33, Salary: 4360, Address: Ahmedabad ID: 8, Name: Mithili, Age: 26, Salary: 4100, Address: Vijayawada ID: 9, Name: Maneesh, Age: 39, Salary: 4000, Address: Hyderabad ID: 10, Name: Rajaneesh, Age: 30, Salary: 6400, Address: Delhi ID: 11, Name: Komal, Age: 29, Salary: 8000, Address: Ahmedabad ID: 12, Name: Manyata, Age: 25, Salary: 5000, Address: Vijayawada
更新于：2019年7月30日
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