jdbc statement对象实例
以下是利用以下三种查询以及打开和关闭说明的例子：
boolean execute(string sql) : 返回一个布尔值true，如果resultset对象可以被检索，否则返回false。使用这个方法来执行sql ddl语句，或当需要使用真正的动态sql。
int executeupdate(string sql) : 返回受影响的sql语句执行的行数。使用此方法来执行，而希望得到一些受影响的行的sql语句 - 例如，insert，update或delete语句。
resultset executequery(string sql) : 返回resultset对象。当希望得到一个结果集使用此方法，就像使用一个select语句。
基于对环境和数据库安装在前面的章节中做此示例代码已被写入。
复制下面的例子中jdbcexample.java，编译并运行，如下所示：
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//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
现在编译上面的例子如下：
c:>javac jdbcexample.java
当运行jdbcexample，它会产生以下结果：
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对象实例
下面是利用callablestatement连同下列getempname()的mysql存储过程的例子：
请确定已经在emp数据库中创建该存储过程。可以使用mysql查询浏览器来完成它。
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 ;
基于对环境和数据库安装在前面的章节中进行，这个范例程式码已被写入。
复制下面的例子中jdbcexample.java，编译并运行，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
现在编译上面的例子如下：
c:>javac jdbcexample.java
当运行jdbcexample，它会产生以下结果：
c:>java jdbcexample
connecting to database... creating statement... executing stored procedure... emp name with id:102 is zaid goodbye!
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