我有一个程序,可以读取mysql数据库表,遍历resultset并返回列表中特定用户id的行数据。在所有可用的互联网资源的帮助下,我成功地创建了一些工作,但我不确定我的实现是否正确。下面是我的dbconnection和daoimpl类。
数据库连接.java
/**
* This class is responsible for creating a new database connection using the declared URL, USER and PASSWORD.
*/
package dbconnection;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
public class DbConnection implements AutoCloseable {
public static final String DB_URL = "jdbc:mysql://localhost:3306/test?autoReconnect=true&useSSL=false";
public static final String USER = "root";
public static final String PWD = "root";
private Connection conn;
/**
* An empty constructor that takes no arguments and creates a new Connection using DriverManager.getConnection.
* The connection is initiated inside a try-with resources with SQLException catch.
*/
public DbConnection() {
try {
conn = DriverManager.getConnection(DB_URL, USER, PWD);
System.out.println("Connection Established.");
} catch (SQLException e) {
System.out.println("Couldn't Connect!! " + e.getMessage());
}
}
//Return the current connection
public Connection getConn() {
return conn;
}
//close
public void close() {
try {
if (conn != null) {
conn.close();
System.out.println("Connection Closed");
}
} catch (SQLException e) {
System.out.println("Couldn't close Connection " + e.getMessage());
}
}
}
tiedostodaoimpl.java文件
import dbconnection.DbConnection;
import pojos.Tiedosto;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
public class TiedostoDaoImpl implements TiedostoDAO {
final String TABLE_TIEDOSTO = "tiedosto";
final String COLUMN_TIEDOSTO_NAME = "nimi";
final String COLUMN_TIEDOSTO_SIZE = "koko_tavua";
final String COLUMN_TIEDOSTO_CONTENT = "sisalto";
final String COLUMN_TIEDOSTO_CUSTOMER_ID = "hlo_id";
final String COLUMN_TIEDOSTO_MINIOUPLOAD = "minioupload";
final String QUERY_TIEDOSTO = "SELECT " + COLUMN_TIEDOSTO_NAME + ", " + COLUMN_TIEDOSTO_CUSTOMER_ID + ", " + COLUMN_TIEDOSTO_SIZE + ", " + COLUMN_TIEDOSTO_CONTENT +
" FROM " + TABLE_TIEDOSTO + " WHERE " + COLUMN_TIEDOSTO_CUSTOMER_ID + " = ?";
final String UPDATE_TIEDOSTO = "UPDATE " + TABLE_TIEDOSTO + " SET " + COLUMN_TIEDOSTO_MINIOUPLOAD + " = 1 WHERE " + COLUMN_TIEDOSTO_CUSTOMER_ID + " = ?";
private DbConnection dbConnection = new DbConnection();
private Connection databaseConnection;
public TiedostoDaoImpl() {
try {
databaseConnection = dbConnection.getConn();
} catch (Exception e) {
System.out.println("Problem Connecting to Database! " + e.getMessage());
}
}
//This method queries tiedosto table and returns the data as a List.
@Override
public List<Tiedosto> getDetails(int userId) throws SQLException {
List<Tiedosto> files;
try (PreparedStatement selectFromTiedosto = databaseConnection.prepareStatement(QUERY_TIEDOSTO)) {
selectFromTiedosto.setInt(1, userId);
try (ResultSet results = selectFromTiedosto.executeQuery()) {
files = new ArrayList<>();
while (results.next()) {
Tiedosto myFile = new Tiedosto();
myFile.setCustomerId(results.getInt(COLUMN_TIEDOSTO_CUSTOMER_ID));
myFile.setFileName(results.getString(COLUMN_TIEDOSTO_NAME));
myFile.setFileSize(results.getInt(COLUMN_TIEDOSTO_SIZE));
myFile.setContent(results.getBlob(COLUMN_TIEDOSTO_CONTENT));
files.add(myFile);
}
}
}
return files;
}
当我运行程序时,我得到如下输出:
当我运行程序时,它会显示“connection established”并返回数据,但不会显示任何关于关闭连接的信息。我需要知道我是否正确地实现了这整件事。有人能帮忙吗?
1条答案
按热度按时间guykilcj1#
你需要包括
DbConnection
在try-with-resource
声明,也许像。。。这将自动关闭两个
DbConnection
以及PreparedStatement
(尽管关闭连接会自动关闭PreparedStatement
无论如何)。缺点是,每次这样使用它,都会创建一个新的
Connection
到数据库,这可能需要时间。更可取的做法可能是使用关闭挂钩或连接池,这取决于您实际在做什么