Java基础之JDBC

JDBC - Java DataBase Connectivity

JDBC 是 Java 面向关系型数据库提供的操作数据库的一套 API (Application Programming Interface)。
JDBC 属于 JavaSE 的一部分。

可以看到下面的类都是接口：

package java.sql;

public interface Connection;
public interface Statement;
public interface ResultSet;


然后每个数据库生产商根据JDBC，提供自己的具体实现类。
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下面是一个基本的JDBC使用过程：

package jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Date;

public class JDBCBasic {

    private Connection connect = null;
    private Statement statement = null;
    private PreparedStatement preparedStatement = null;
    private ResultSet resultSet = null;

    public void readDataBase() throws Exception {
        try {
            //1. This will load the MySQL driver, each DB has its own driver
            Class.forName("com.mysql.jdbc.Driver");
            
            //2. Setup the connection with the DB
            connect = DriverManager
                    .getConnection("jdbc:mysql://localhost/feedback?"
                            + "user=sqluser&password=sqluserpw");
            // or
            // DriverManager.getConnection(
            //         "jdbc:mysql://localhost/feedback", "sqluser", "sqluserpw");

            //3.1 Statements allow to issue SQL queries to the database
            statement = connect.createStatement();
            
            //4.1 Result set get the result of the SQL query
            resultSet = statement.executeQuery("select * from feedback.comments");
            writeResultSet(resultSet);

            //3.2 PreparedStatements can use variables and are more efficient
            preparedStatement = connect
                    .prepareStatement("insert into  feedback.comments values (default, ?, ?, ?, ? , ?, ?)");
            // "myuser, webpage, datum, summary, COMMENTS from feedback.comments");
            // Parameters start with 1
            preparedStatement.setString(1, "Test");
            preparedStatement.setString(2, "TestEmail");
            preparedStatement.setString(3, "TestWebpage");
            preparedStatement.setDate(4, new java.sql.Date(2009, 12, 11));
            preparedStatement.setString(5, "TestSummary");
            preparedStatement.setString(6, "TestComment");
            
            //4.2
            preparedStatement.executeUpdate();

            preparedStatement = connect
                    .prepareStatement("SELECT myuser, webpage, datum, summary, COMMENTS from feedback.comments");
            //4.3
            resultSet = preparedStatement.executeQuery();
            writeResultSet(resultSet);

            // Remove again the insert comment
            preparedStatement = connect
                    .prepareStatement("delete from feedback.comments where myuser= ? ; ");
            preparedStatement.setString(1, "Test");
            preparedStatement.executeUpdate();

            resultSet = statement
                    .executeQuery("select * from feedback.comments");
            writeMetaData(resultSet);

        } catch (Exception e) {
            throw e;
        } finally {
            close();
        }

    }

    private void writeMetaData(ResultSet resultSet) throws SQLException {
        // Now get some metadata from the database
        // Result set get the result of the SQL query

        System.out.println("The columns in the table are: ");

        System.out.println("Table: " + resultSet.getMetaData().getTableName(1));
        for (int i = 1; i <= resultSet.getMetaData().getColumnCount(); i++) {
            System.out.println("Column " + i + " "
                    + resultSet.getMetaData().getColumnName(i));
        }
    }

    private void writeResultSet(ResultSet resultSet) throws SQLException {
        // ResultSet is initially before the first data set
        while (resultSet.next()) {
            // It is possible to get the columns via name
            // also possible to get the columns via the column number
            // which starts at 1
            // e.g. resultSet.getSTring(2);
            String user = resultSet.getString("myuser");
            String website = resultSet.getString("webpage");
            String summary = resultSet.getString("summary");
            Date date = resultSet.getDate("datum");
            String comment = resultSet.getString("comments");
            System.out.println("User: " + user);
            System.out.println("Website: " + website);
            System.out.println("summary: " + summary);
            System.out.println("Date: " + date);
            System.out.println("Comment: " + comment);
        }
    }

    // You need to close the resultSet
    private void close() {
        try {
            if (resultSet != null) {
                resultSet.close();
            }

            if (statement != null) {
                statement.close();
            }

            if (connect != null) {
                connect.close();
            }
        } catch (Exception e) {

        }
    }

}