Question

我有一个java项目，其中包含许多连接到数据库的文件。任何人都可以告诉我是否可以使用java类文件连接到数据库，这样我就不会为每个文件创建数据库连接，请教我如何...感谢您的帮助：D 这是我使用的代码，但它不起作用

dbConnect.java - 类文件

    public class dbConnect {

        public static void connect(){
        Connection conn;
        Statement stmt;
        ResultSet rs;

        String sql;
            conn = null;
            String url = "jdbc:mysql://localhost:3306/db_oopproject";
            String driver = "com.mysql.jdbc.Driver";
            try{
                Class.forName(driver).newInstance();
                conn = DriverManager.getConnection(url,"user","12345");

                stmt = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);
                sql = "Select * from user_account";
                rs = stmt.executeQuery(sql);

            }
            catch (Exception e){
                System.out.print(e.getMessage());
            }
        }


    }

我使用这个dbConnect.connect（）在主文件中调用了这个类; 代码有什么问题吗？

Answer 1

将数据库连接代码放在一个类中，并在任何您喜欢的地方使用它。

这样的事情可以是一个好的开始：

package persistence;

import java.sql.*;
import java.util.*;

/**
 * util.DatabaseUtils
 * User: Michael
 * Date: Aug 17, 2010
 * Time: 7:58:02 PM
 */
public class DatabaseUtils {
    private static final String DEFAULT_DRIVER = "oracle.jdbc.driver.OracleDriver";
    private static final String DEFAULT_URL = "jdbc:oracle:thin:@host:1521:database";
    private static final String DEFAULT_USERNAME = "username";
    private static final String DEFAULT_PASSWORD = "password";
/*
    private static final String DEFAULT_DRIVER = "org.postgresql.Driver";
    private static final String DEFAULT_URL = "jdbc:postgresql://localhost:5432/party";
    private static final String DEFAULT_USERNAME = "pgsuper";
    private static final String DEFAULT_PASSWORD = "pgsuper";
*/
/*
    private static final String DEFAULT_DRIVER = "com.mysql.jdbc.Driver";
    private static final String DEFAULT_URL = "jdbc:mysql://localhost:3306/party";
    private static final String DEFAULT_USERNAME = "party";
    private static final String DEFAULT_PASSWORD = "party";
*/

    public static void main(String[] args) {
        long begTime = System.currentTimeMillis();

        String driver = ((args.length > 0) ? args[0] : DEFAULT_DRIVER);
        String url = ((args.length > 1) ? args[1] : DEFAULT_URL);
        String username = ((args.length > 2) ? args[2] : DEFAULT_USERNAME);
        String password = ((args.length > 3) ? args[3] : DEFAULT_PASSWORD);

        Connection connection = null;
        // No, I loaded the driver as I intended.  It's correct.  The edit is not.
        try {
            connection = createConnection(driver, url, username, password);
            DatabaseMetaData meta = connection.getMetaData();
            System.out.println(meta.getDatabaseProductName());
            System.out.println(meta.getDatabaseProductVersion());

            String sqlQuery = "SELECT PERSON_ID, FIRST_NAME, LAST_NAME FROM PERSON ORDER BY LAST_NAME";
            System.out.println("before insert: " + query(connection, sqlQuery, Collections.EMPTY_LIST));

            connection.setAutoCommit(false);
            String sqlUpdate = "INSERT INTO PERSON(FIRST_NAME, LAST_NAME) VALUES(?,?)";
            List parameters = Arrays.asList("Foo", "Bar");
            int numRowsUpdated = update(connection, sqlUpdate, parameters);
            connection.commit();

            System.out.println("# rows inserted: " + numRowsUpdated);
            System.out.println("after insert: " + query(connection, sqlQuery, Collections.EMPTY_LIST));
        } catch (Exception e) {
            rollback(connection);
            e.printStackTrace();
        } finally {
            close(connection);
            long endTime = System.currentTimeMillis();
            System.out.println("wall time: " + (endTime - begTime) + " ms");
        }
    }

    public static Connection createConnection(String driver, String url, String username, String password) throws ClassNotFoundException, SQLException {
        Class.forName(driver);
        if ((username == null) || (password == null) || (username.trim().length() == 0) || (password.trim().length() == 0)) {
            return DriverManager.getConnection(url);
        } else {
            return DriverManager.getConnection(url, username, password);
        }
    }

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


    public static void close(Statement st) {
        try {
            if (st != null) {
                st.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

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

    public static void rollback(Connection connection) {
        try {
            if (connection != null) {
                connection.rollback();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public static List<Map<String, Object>> map(ResultSet rs) throws SQLException {
        List<Map<String, Object>> results = new ArrayList<Map<String, Object>>();
        try {
            if (rs != null) {
                ResultSetMetaData meta = rs.getMetaData();
                int numColumns = meta.getColumnCount();
                while (rs.next()) {
                    Map<String, Object> row = new HashMap<String, Object>();
                    for (int i = 1; i <= numColumns; ++i) {
                        String name = meta.getColumnName(i);
                        Object value = rs.getObject(i);
                        row.put(name, value);
                    }
                    results.add(row);
                }
            }
        } finally {
            close(rs);
        }
        return results;
    }

    public static List<Map<String, Object>> query(Connection connection, String sql, List<Object> parameters) throws SQLException {
        List<Map<String, Object>> results = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            ps = connection.prepareStatement(sql);

            int i = 0;
            for (Object parameter : parameters) {
                ps.setObject(++i, parameter);
            }
            rs = ps.executeQuery();
            results = map(rs);
        } finally {
            close(rs);
            close(ps);
        }
        return results;
    }

    public static int update(Connection connection, String sql, List<Object> parameters) throws SQLException {
        int numRowsUpdated = 0;
        PreparedStatement ps = null;
        try {
            ps = connection.prepareStatement(sql);

            int i = 0;
            for (Object parameter : parameters) {
                ps.setObject(++i, parameter);
            }
            numRowsUpdated = ps.executeUpdate();
        } finally {
            close(ps);
        }
        return numRowsUpdated;
    }
}

Answer 2

您必须使用数据库连接池。

点击此链接：http://www.snaq.net/java/DBPool/

Answer 3

您必须创建简单的java类文件以连接到数据库，并在需要时调用该类的对象。

Answer 4

你可以这样做：

class DBConnector{
static Connection c;
public static Connection getConnection(){

    try{ 
    Class.forName("your fully qualified driver class name");
    c = DriverManager.getConnection("connection url");
    return c;
    }catch(Exception e){
    return null;
    }

}
}

每当需要新的数据库连接时调用此方法

Answer 5

尝试使用http://www.mchange.com/projects/c3p0/这很容易配置。

Answer 6

当创建对象的成本高于使用对象时，数据库连接池非常有用。这通常是数据库连接的情况，因为数据库和您的服务器需要协商连接并处理身份验证等。还需要在服务器端和数据库端完成工作以分配必要的发送结构数据。如果您使用的是SSL，那么另一个因素会导致创建连接速度变慢。

如果您需要打开然后关闭许多连接，那么您可能需要使用池。当然，如果不了解您的申请细节，很难说。

我写了一篇关于这个主题的文章，详细介绍了一下。阅读之后，你应该有足够的理解来了解这对你是否有意义。

你可以在这里阅读：

http://innolitics.com/10x/database-pools/

Java DB连接

6 个答案: