2016.5.23 Mybatis Framework (ii) a summary of the original ecological JDBC Program

JDBC Program

1. Create a Java project to join the JAR package

Database driver package (MySQL)

In fact, only the top of the drive package, because the use of MySQL, the general version is not a problem, this machine is MySQL 5.6

Below is the Oracle driver package

2. Create a Jdbctest project

1  PackageCn.itcast.mybatis.jdbc;2 3 Importjava.sql.Connection;4 ImportJava.sql.DriverManager;5 Importjava.sql.PreparedStatement;6 ImportJava.sql.ResultSet;7 Importjava.sql.SQLException;8 9 Ten  Public classJdbctest { One      Public Static voidMain (string[] args)throwssqlexception{ A         //Database Links -Connection Connection =NULL; -         //Precompiled statement, using precompilation to improve database performance thePreparedStatement PreparedStatement =NULL; -         //result set -ResultSet resultset=NULL; -          +         Try{ -             //Load Database driver +Class.forName ("Com.mysql.jdbc.Driver"); A              atConnection = Drivermanager.getconnection ("Jdbc:mysql://127.0.0.1:3306/test?characterencoding=utf-8", "Root", "" "); -String sql = "SELECT * from user where username =?" and id =? "; -PreparedStatement =connection.preparestatement (SQL); -              -Preparedstatement.setstring (1, "Harry"); -Preparedstatement.setstring (2, "1"); in              -ResultSet =preparedstatement.executequery (); to              +              while(Resultset.next ()) { -System.out.println (resultset.getstring ("id") +resultset.getstring ("username"))); the             } *}Catch(Exception e) { $ e.printstacktrace ();Panax Notoginseng}finally{ - resultset.close (); the preparedstatement.close (); + Connection.close ();  A         } the     } +}

3. JDBC uses drivers

What is JDBC full name?

Java DataBase Connectivity

That is, the Java database connection is established

Then the 3 areas required

1> established link object Connection Connection

2> The precompiled Statement Declaration object established PreparedStatement PreparedStatement

3> query to the result set object ResultSet ResultSet

Next is the process of how to use JDBC for database linking and manipulation

1> Load Driver Class.forName (com.mysql.jdbc.Driver);

Locate the Driver.class file in the driver package, copy QualifiedName.

2> assigning url+ ports to link connection

Conneciton = Drivermanager.getconnection ("Jdbc:mysql://127.0.0.1:3306/test", "Test", "");

Format JDBC: Database type name://Address: Port/Database name username UserPassword

3> defines what SQL statement to execute

String sql = "SELECT * from user where username =?" and id=? "

Position symbol "?" The role of a reserved field is saved by the committed value of the pending

Preparedstatement.setstring (Index, "value");

The first one is the question mark, the second one is the value.

Actually replaced? The form ' value ' so obviously cannot replace some property names such as column

4> executes this precompiled return result set

ResultSet = Preparedstatement.executequerry ();

Query values can be obtained by entering the corresponding column property in the result set

Resultset.getstring ("id")

5> Releasing Resources

Order Upside Down: Resultset.close () Preparedstatement.close () Connection.close ()

4. Original Eco-JDBC Problem:

1> database connection, when used to create non-use immediate release, frequent connection and shutdown of the database, resulting in data resource waste affecting database performance

Harry--Database connection pool

2> SQL statements in Java code, this is a hard-coded way, if the SQL statement is modified, you need to recompile the Java code,

Set parameters in PreparedStatement, also hard coded in Java code

Harry---SQL statements, placeholders and other variables are placed in the XML file to be configured

3> result set ResultSet still hard-coded to get table field

Harry automatically map a query's result set to a Java object

2016.5.23 Mybatis Framework (ii) a summary of the original ecological JDBC Program