JDBC-语句对象例子
JDBC-语句对象例子
下面的例子利用三种查询语句:
示例代码基于之前设置的环境和数据库编写。
复制粘贴代码到JDBCExample.java,编译运行如下:
编译上述代码:
当你运行JDBCExample的时候,产生如下输出:
下面的例子利用三种查询语句:
- boolean execute(String SQL):如果ResultSet对象可以被检索,则返回一个布尔真值;否则,它将返回false。用这个方法来执行SQL DDL语句或使用真正的动态SQL。
- int executeUpdate(String SQL):由执行的SQL语句返回影响的行数量。使用这个方法来执行SQL语句,返回行数,例如,一个插入、更新或删除语句。
- ResultSet executeQuery(String SQL):返回一个记录集对象。当你期望得到一个结果集的时候使用这个方法,就像使用SELECT语句。
示例代码基于之前设置的环境和数据库编写。
复制粘贴代码到JDBCExample.java,编译运行如下:
//STEP 1. Import required packages import java.sql.*; public class JDBCExample { // JDBC driver name and database URL static final String JDBC_DRIVER = "com.mysql.jdbc.Driver"; static final String DB_URL = "jdbc:mysql://localhost/EMP"; // Database credentials static final String USER = "username"; static final String PASS = "password"; public static void main(String[] args) { Connection conn = null; Statement stmt = null; try{ //STEP 2: Register JDBC driver Class.forName("com.mysql.jdbc.Driver"); //STEP 3: Open a connection System.out.println("Connecting to database..."); conn = DriverManager.getConnection(DB_URL,USER,PASS); //STEP 4: Execute a query System.out.println("Creating statement..."); stmt = conn.createStatement(); String sql = "UPDATE Employees set age=30 WHERE id=103"; // Let us check if it returns a true Result Set or not. Boolean ret = stmt.execute(sql); System.out.println("Return value is : " + ret.toString() ); // Let us update age of the record with ID = 103; int rows = stmt.executeUpdate(sql); System.out.println("Rows impacted : " + rows ); // Let us select all the records and display them. sql = "SELECT id, first, last, age FROM Employees"; ResultSet rs = stmt.executeQuery(sql); //STEP 5: Extract data from result set while(rs.next()){ //Retrieve by column name int id = rs.getInt("id"); int age = rs.getInt("age"); String first = rs.getString("first"); String last = rs.getString("last"); //Display values System.out.print("ID: " + id); System.out.print(", Age: " + age); System.out.print(", First: " + first); System.out.println(", Last: " + last); } //STEP 6: Clean-up environment rs.close(); stmt.close(); conn.close(); }catch(SQLException se){ //Handle errors for JDBC se.printStackTrace(); }catch(Exception e){ //Handle errors for Class.forName e.printStackTrace(); }finally{ //finally block used to close resources try{ if(stmt!=null) stmt.close(); }catch(SQLException se2){ }// nothing we can do try{ if(conn!=null) conn.close(); }catch(SQLException se){ se.printStackTrace(); }//end finally try }//end try System.out.println("Goodbye!"); }//end main }//end JDBCExample
编译上述代码:
C:>javac JDBCExample.java C:>
当你运行JDBCExample的时候,产生如下输出:
C:>java JDBCExample Connecting to database... Creating statement... Return value is : false Rows impacted : 1 ID: 100, Age: 18, First: Zara, Last: Ali ID: 101, Age: 25, First: Mahnaz, Last: Fatma ID: 102, Age: 30, First: Zaid, Last: Khan ID: 103, Age: 30, First: Sumit, Last: Mittal Goodbye! C:>