JDBC -- extract JDBC tool classes

Catalog

1、 Extract the code to obtain the database connection object  

2、 Extract the registration driver code

3、 Methods of extracting and closing resources

4、 test

5、 Extract the configuration file

6、 Complete tool class code

The use of jdbc The code repetition of adding, deleting, modifying and checking the database is relatively high , Extract the repeated code into a tool class for code reuse , Simplify coding

First, observe which code has high repeatability ：

Next write Jdbcutil Tool class

1、 Extract the code to obtain the database connection object  

First, we want to get the database connection object that encapsulates the database connection information through the tool class connection

So you need to be in JdbcUtil Write a method The return is connection

  Pass in the database connection information through parameters ：

2、 Extract the registration driver code

  You need to register drivers , First think of using static Static code block Load static code blocks as classes load Register driver

So when we use jdbcUtil Class when loading JdbcUtil Class, the driver will be registered

3、 Methods of extracting and closing resources

Get the method of overload writing to close resources through method The parameters passed are different The methods called are different  

/**
     *  Release resources 
     *
     * @param stmt
     * @param conn
     */
    public static void close(Statement stmt, Connection conn) {
        if (stmt != null) {
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
    public static void close(PreparedStatement pstmt, Connection conn) {
        if (pstmt != null) {
            try {
                pstmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }


    /**
     *  Release resources 
     *
     * @param stmt
     * @param conn
     */
    public static void close(ResultSet rs, Statement stmt, Connection conn) {
        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (stmt != null) {
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
    public static void close(ResultSet rs, PreparedStatement stmt, Connection conn) {
        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (stmt != null) {
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

4、 test

Inquire about

// jdbc Tool class test 
public class JdbcUtilTest {
    public static void main(String[] args) {
        ResultSet resultSet = null;
        Connection connection = null;
        Statement statement = null;

        try {
            // 1、 Registration drive   Get database connection object 
            connection = JdbcUtil.getConnection();
            // 2、 Print connection object   See if you can get the database connection object 
//            System.out.println(connection);

            //  Definition sql
            String sql = "select * from person";
            //  Access to perform sql The object of 
            statement = connection.createStatement();
            //  perform sql The query 
            resultSet = statement.executeQuery(sql);
            //  Process query results 
            while (resultSet.next()) {
                System.out.println(resultSet.getString("name") + "---" + resultSet.getString("email"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            //  Release resources   Calling tool class close Method 
            JdbcUtil.close(resultSet,statement,connection);
        }

    }
}

---

But we found the database connection information such as driver url User passwords and other information are still with java Code coupling is dead ,

In the future, we need to modify the database information , For example, when connecting to another database, you need to find the java Code modification , Very not what we want .

So we need to extract the database connection information separately Form a configuration file

Continue to improve the tool class code

5、 Extract the configuration file

stay src So let's make a new one properties file Fill in the database connection information

  modify JdbcUtil Code

Read configuration file

  test ：

 

6、 Complete tool class code

package com.zhou.utils;

import java.io.IOException;
import java.io.InputStream;
import java.sql.*;
import java.util.Properties;


//  This is a jdbc Tool class of 
public class JdbcUtil {
    private static String url;
    private static String user;
    private static String passwd;
    private static String driver;


    static {
        try {
            // 1、 establish properties Collection classes 
            Properties properties = new Properties();
            // 2、 Load profile 
            InputStream resourceAsStream = JdbcUtil.class.getClassLoader().getResourceAsStream("db.properties");
            properties.load(resourceAsStream);
            url = properties.getProperty("url");
            user = properties.getProperty("user");
            passwd = properties.getProperty("password");
            driver = properties.getProperty("driver");

            //  Registration drive 
            Class.forName(driver);

        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
     *  Get database connection object 
     * @return  Data connection objects 
     */
    public static Connection getConnection() throws SQLException {
        return DriverManager.getConnection(url,user,passwd);
    }
    /**
     *  Release resources 
     *
     * @param stmt
     * @param conn
     */
    public static void close(Statement stmt, Connection conn) {
        if (stmt != null) {
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
    public static void close(PreparedStatement pstmt, Connection conn) {
        if (pstmt != null) {
            try {
                pstmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }


    /**
     *  Release resources 
     *
     * @param stmt
     * @param conn
     */
    public static void close(ResultSet rs, Statement stmt, Connection conn) {
        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (stmt != null) {
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
    public static void close(ResultSet rs, PreparedStatement stmt, Connection conn) {
        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (stmt != null) {
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

}