Java的JDBC中Statement與CallableStatement對象實例
JDBC Statement對象實例
以下是利用以下三種查詢以及打開和關(guān)閉說明的例子:
boolean execute(String SQL) : 返回一個布爾值true,如果ResultSet對象可以被檢索,否則返回false。使用這個方法來執(zhí)行SQL DDL語句,或當需要使用真正的動態(tài)SQL。
int executeUpdate(String SQL) : 返回受影響的SQL語句執(zhí)行的行數(shù)。使用此方法來執(zhí)行,而希望得到一些受影響的行的SQL語句 - 例如,INSERT,UPDATE或DELETE語句。
ResultSet executeQuery(String SQL) : 返回ResultSet對象。當希望得到一個結(jié)果集使用此方法,就像使用一個SELECT語句。
基于對環(huán)境和數(shù)據(jù)庫安裝在前面的章節(jié)中做此示例代碼已被寫入。
復(fù)制下面的例子中JDBCExample.java,編譯并運行,如下所示:
//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
現(xiàn)在編譯上面的例子如下:
C:>javac JDBCExample.java
當運行JDBCExample,它會產(chǎn)生以下結(jié)果:
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!
JDBC CallableStatement對象實例
下面是利用CallableStatement連同下列g(shù)etEmpName()的MySQL存儲過程的例子:
請確定已經(jīng)在EMP數(shù)據(jù)庫中創(chuàng)建該存儲過程。可以使用MySQL查詢?yōu)g覽器來完成它。
DELIMITER $$ DROP PROCEDURE IF EXISTS `EMP`.`getEmpName` $$ CREATE PROCEDURE `EMP`.`getEmpName` (IN EMP_ID INT, OUT EMP_FIRST VARCHAR(255)) BEGIN SELECT first INTO EMP_FIRST FROM Employees WHERE ID = EMP_ID; END $$ DELIMITER ;
基于對環(huán)境和數(shù)據(jù)庫安裝在前面的章節(jié)中進行,這個范例程式碼已被寫入。
復(fù)制下面的例子中JDBCExample.java,編譯并運行,如下所示:
//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;
CallableStatement 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...");
String sql = "{call getEmpName (?, ?)}";
stmt = conn.prepareCall(sql);
//Bind IN parameter first, then bind OUT parameter
int empID = 102;
stmt.setInt(1, empID); // This would set ID as 102
// Because second parameter is OUT so register it
stmt.registerOutParameter(2, java.sql.Types.VARCHAR);
//Use execute method to run stored procedure.
System.out.println("Executing stored procedure..." );
stmt.execute();
//Retrieve employee name with getXXX method
String empName = stmt.getString(2);
System.out.println("Emp Name with ID:" +
empID + " is " + empName);
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
現(xiàn)在編譯上面的例子如下:
C:>javac JDBCExample.java
當運行JDBCExample,它會產(chǎn)生以下結(jié)果:
C:>java JDBCExample
Connecting to database... Creating statement... Executing stored procedure... Emp Name with ID:102 is Zaid Goodbye!
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