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？
答案 0 :(得分：3)
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;
}
}
答案 1 :(得分：1)
您必须使用数据库连接池。
答案 2 :(得分：1)
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。
答案 3 :(得分：0)
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
答案 4 :(得分：0)
尝试使用http://www.mchange.com/projects/c3p0/这很容易配置。
答案 5 :(得分：0)
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：