Use of JDBC

Interfaces and procedures

Import jdbc Drive pack

Ojdbc6.jar Download link

Load database driver

Class.forName(“com.mysql.jdbc.Driver”); //mysql
Class.forName(" oracle.jdbc.driver.OracleDriver"); //oracle

Create database link objects

DriverManager class

effect ：1) Manage and register drivers . 2) Create a connection to the database .
Methods in class ：

DriverManager Static methods in a class	describe
Connection getConnection (String url, String user, String password)	By concatenating strings , user name , The password gets the data Library connection object
Connection getConnection (String url, Properties info)	By concatenating strings , Property object to get the connection object

database URL
Common databases URL How to write the address ：
Oracle：jdbc:oracle:thin:@localhost:1521:orcl
SqlServer：jdbc:microsoft:sqlserver://localhost:1433; DatabaseName=shen
MySql：jdbc:mysql://localhost:3306/shen

Connection

A connection to a specific database （ conversation ）. Execute in the connection context SQL Statement and return the result .
Collection Is the most important object in database programming , All the interaction between the client and the database is through connection Object completed , The creation method is ：

Connection conn = DriverManager.getConnection(url,user,pass);

Common methods of this object ：

Method	describe
createStatement()	Create send to database sql Of statement object .
prepareStatement(sql)	Create send precompile to database sql Of PrepareSatement object .
prepareCall(sql)	Create the... That executes the stored procedure callableStatement object .
setAutoCommit(boolean autoCommit)	Set whether transactions are automatically committed .
commit()	Commit a transaction on a link .
rollback()	Roll back transactions on this link .

String url = "jdbc:oracle:thin:@localhost:1521:orcl";
String username = "scott";
String password = "tiger";
Connection conn = null;
			
//2. Get a link to the database 
conn = DriverManager.getConnection(url, username, password);

establish statement object

Statement

For execution static SQL Statement and returns the object for which it generated the result .
All known sub interfaces ： CallableStatement, PreparedStatement .
Jdbc In program Statement Object to send... To the database SQL sentence , The creation method is ：

Statement stmt = conn.createStatement();

Statement Common methods of objects ：

Method	meaning
executeQuery(String sql)	Used to send query statements to data .
executeUpdate(String sql)	Used to send... To a database insert、update or delete sentence
execute(String sql)	Used to send arbitrary... To the database sql sentence
addBatch(String sql)	Put more than one sql Statement in a batch .
executeBatch()	Send a batch of sql Statement execution .

Statement stmt = null;
//3. Get to send... To the database sql Of the statement statement
stmt = conn.createStatement();
//4. Send... To the database sql
String sql = "select empno,ename,sal from emp";
stmt.executeQuery(sql);

PrepareStatement

Represents precompiled SQL Object of statement .
All known sub interfaces ： CallableStatement
Its instance object can be called by ：

PreperedStatement pstm = conn.preparedStatement()

PreperedStatement pstm = null;
String sql = "select * from users where name=? and password=?";
 
//3. Get to send... To the database sql Of the statement Preperedstatement
pstm = conn.preparedStatement(sql);// In this time , Precompile 
pstm.setString(1, username);
pstm.setString(2, password);
//4. Send... To the database sql
pstm.executeQuery();// There's no need to pass in sql

Compare ： be relative to Statement In terms of objects

• PreperedStatement You can avoid SQL Injection problem .
  Such as ：String sql=“select * from admin where loginname=’”+loginName+"+and loginpwd=’"+loginPwd+"’";
  In the application ：
  -》 Please enter your account number ： 333
  -》 Please input a password ： wer’or’1’='1
  Actually sending ：select * from admin where loginname=‘333’ and loginpwd=‘wer’or’1’=‘1’, Login successful ！
• Statement Will cause the database to compile frequently SQL, May cause database buffer overflow .PreparedStatement But for SQL Precompile , So as to improve the efficiency of database execution .
• also PreperedStatement about sql Parameters in , Allow substitution in the form of placeholders , simplify sql Statement writing .

CallableStatement

Used to perform SQL The interface of the stored procedure .

Populate result set

Jdbc In program ResultSet Used to represent Sql Statement execution result .Resultset When encapsulating execution results , In a tabular way ,ResultSet Object maintains a cursor pointing to a table data row , In the beginning , The cursor is before the first line , call ResultSet.next() Method , You can make the cursor point to a specific row of data , Call the method to get the data of the row .

ResultSet

A data table that represents a database result set , Typically generated by executing statements that query the database .

1、 Get row

1. ResultSet Provides a way to scroll the result set ：
   next()： Move to next line
   Previous()： Move to previous line
   absolute(int row)： Move to specified row
   beforeFirst()： Move resultSet Foremost .
   afterLast() ： Move to resultSet At the back of .

2、 Get value

1. ResultSet Since it is used to encapsulate the execution result , So what this object provides is for getting data get Method ：
   Get any type of data
   getObject(int index)
   getObject(string columnName)
   Get data of the specified type , for example ：
   getString(int index)
   getString(String columnName)

ResultSet rs = null;
//4. Send... To the database sql, And get the resultset
String sql = "select empno,enamesal,birthday from emp";
rs = pstm.executeQuery(sql);			

About ResultSet Note in interface ：

1. If the cursor is before the first line , Use rs.getXX() Get column values , Report errors ：Before start of result set
2. If the cursor is after the last line , Use rs.getXX() Get column values , Report errors ：After end of result set
3. Close the result set after use ResultSet, To shut down Statement, To shut down Connection

Traversal result set

//5. Take out the data of the result set 
rs.afterLast();
rs.previous();
System.out.println("id=" + rs.getInt("empno"));
System.out.println("name=" + rs.getStringt("name"));
System.out.println("password=" + rs.getDouble("sal"));
System.out.println("birthday=" + rs.getObject("birthday"));

// Cycle out 
while (rs.next()) {
    				
	System.out.println(rs.getInt("empno")+"\t"+rs.getString("ename")+"\t"+
rs.getDouble("sal"));
	}

Close the connection

Jdbc After the program runs , Remember to release the program while it is running , The objects created to interact with the database , These objects are usually ResultSet, Statement and Connection object .
Be careful ： To ensure that the resource release code can run , Resource release code must also be placed in finally In the sentence .

1. Objects that need to be released ：ResultSet Result set ,Statement sentence ,Connection Connect
2. Release principle ： Open first, then close , Turn off the last one .ResultSet  Statement  Connection
3. In which code block ：finally block

//7. Close links , Release resources 
finally {
    
	  try {
    
		if(rs!=null) {
    		
			 rs.close();		
		 	rs =null;
		}
		if(stmt!=null) {
    	
			stmt.close();
			stmt =null;
		}
		if(conn!=null) {
    	
			conn.close();
			conn =null;
		}
	} catch (SQLException e) {
    
	// TODO Auto-generated catch block
			e.printStackTrace();
	}
}

JDBC Configuration and use

//  First step ：  First register the driver ,  Drivers are usually registered only once 
try {
    
       Class.forName("com.mysql.jdbc.Driver");
    } catch (ClassNotFoundException e) {
    
       // TODO Auto-generated catch block
       e.printStackTrace();
    }
//  The second step ： Establishing a connection  Connect,  Set up url , user name ,  password 
   // url Format ：JDBC: Sub protocol : Child name // Host name : port / Database name ？ Property name = Property value &…
   //  Pay attention to is url There must be no extra space in the , Otherwise it will go wrong , useSSL=false To solve the problem of warnings during authentication 
   // String url = "jdbc:mysql://localhost:3306/test?" + "user=root&password=wsw011152&useUnicode=true&characterEncoding=UTF-8&useSSL=false";
      String url = "jdbc:mysql://localhost:3306/test?useSSL=false";
      String name = "root";
      String psw = "******";
      Connection connect = null;
try {
    
    connect = DriverManager.getConnection(url, name, psw);
    // connect = DriverManager.getConnection(url);
    } catch (SQLException e) {
    
     // TODO Auto-generated catch block
      e.printStackTrace();
    }
 //  The third step ：  Create a  Statement , It is generally recommended to use  PreparedStatement
        // 1、 Perform static SQL sentence . Usually by Statement Instance implementation .
        // 2、 Execution dynamics SQL sentence . Usually by PreparedStatement Instance implementation .
        // 3、 Execute database stored procedures . Usually by CallableStatement Instance implementation .
        // String sql = "select * from user where id = ?";
        String sql = "select * from user where id = ?";
try {
    
     PreparedStatement ps = connect.prepareStatement(sql);
     ps.setInt(1, 1); //  Set parameters 
 //  Step four :  Execute statement , Get a result set , Process the results obtained 
     ResultSet result = ps.executeQuery();
      while (result.next()){
                
      			System.out.println(result.getInt("id"));
                System.out.println(result.getString("name"));
                System.out.println(result.getInt("age"));
                System.out.println(result.getString("salary"));
      }
 //  Step five ：  close resource 
     result.close();
     ps.close();
     connect.close();
    } catch (SQLException e) {
    
      // TODO Auto-generated catch block
       e.printStackTrace();
    }
  }