Java的JDBC中Statement与CallableStatement对象实例

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：

//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!