我开发了一个Java的Web应用程序，它使用JDBC连接器连接到MySQL数据库，并创建2个连接池。该应用程序部署在tomcat服务器上。
我的问题是，如果我多次部署应用程序，并且当我关闭tomcat时，代码没有任何行来关闭可用连接，那么这段代码会影响MySQL可用连接吗？重新启动时tomcat会负责关闭连接吗？
连接Util：
import javax.sql.DataSource;
import org.apache.commons.dbcp.ConnectionFactory;
import org.apache.commons.dbcp.DriverManagerConnectionFactory;
import org.apache.commons.dbcp.PoolableConnectionFactory;
import org.apache.commons.dbcp.PoolingDataSource;
import org.apache.commons.pool.impl.GenericObjectPool;
public class MySQLConnectionPool {
public static DataSource setUpPool(){
GenericObjectPool gPool = null;
String dbName = "DBName";
String userName = "Username";
String password = "Password";
String hostname = "Host";
String port = "Port";
try {
Class.forName("com.mysql.jdbc.Driver");
// Creates an Instance of GenericObjectPool That Holds Our Pool of Connections Object!
gPool = new GenericObjectPool();
gPool.setMaxActive(2);
// Creates a ConnectionFactory Object Which Will Be Use by the Pool to Create the Connection Object!
ConnectionFactory cf = new DriverManagerConnectionFactory("jdbc:mysql://" + hostname + ":" + port + "/" + dbName, userName, password);
// Creates a PoolableConnectionFactory That Will Wraps the Connection Object Created by the ConnectionFactory to Add Object Pooling Functionality!
PoolableConnectionFactory pcf = new PoolableConnectionFactory(cf, gPool, null, null, false, true);
}catch (Exception e) {
// TODO: handle exception
System.out.println("Error: "+e.toString());
}
return new PoolingDataSource(gPool);
}
}
DAO：
@Override
public ArrayList<User> getUserDetails(String environment, String MySQLQuery) {
// TODO Auto-generated method stub
ArrayList<User> users = new ArrayList<User>();
Connection connObj = null;
Statement stmt = null;
ResultSet result = null;
try {
DataSource dataSource = MySQLConnectionPool.setUpPool();
// Performing Database Operation!
System.out.println("\n=====Making A New Connection Object For Db Transaction=====\n");
connObj = dataSource.getConnection();
stmt = connObj.createStatement();
result = stmt.executeQuery(MySQLQuery);
while(result.next()) {
//Some code here
}
System.out.println("\n=====Releasing Connection Object To Pool=====\n");
} catch(Exception sqlException) {
} finally {
try {
// Closing ResultSet Object
if(result != null) {
result.close();
}
// Closing Statement Object
if(stmt != null) {
stmt.close();
}
// Closing Connection Object
if(connObj != null) {
connObj.close();
}
} catch(Exception sqlException) {
}
}
return users;
}
如果停止整个tomcat，则与数据库的连接将关闭，因为运行Tomcat的java可执行文件将在停止时释放连接。
即使你不停止服务器，如果Java决定你的Connection对象不再使用，那么它将被垃圾回收。你只是不知道什么时候。
另一方面：
DataSource嵌入服务器并从服务器获取DataSource的方法：此页面可能会有所帮助。使用资源尝试：
DataSource dataSource = MySQLConnectionPool.setUpPool();
try (Connection connObj = dataSource.getConnection()) {
try (Statement stmt = connObj.createStatement()) {
try (ResultSet result = stmt.executeQuery(MySQLQuery)) {
while(result.next()) {
//Some code here
}
}
}
} catch (SQLException sqlException) {
// do something
}
或者：
DataSource dataSource = MySQLConnectionPool.setUpPool();
try (Connection connObj = dataSource.getConnection();
Statement stmt = connObj.createStatement();
ResultSet result = stmt.executeQuery(MySQLQuery)
) {
while(result.next()) {
//Some code here
}
} catch (SQLException sqlException) {
// do something
}
正如我上面所说，您的代码是错误的，因为您在关闭ResultSet或语句时可能会出现异常（至少是SQLException），因此您的代码永远不会释放后面的对象：
try {
// Closing ResultSet Object
if(result != null) {
result.close(); // if it fails, stmt and connObj are not closed.
}
// Closing Statement Object
if(stmt != null) {
stmt.close(); // if it fails, connObj is not closed.
}
// Closing Connection Object
if(connObj != null) {
connObj.close();
}
} catch(Exception sqlException) {
}
如果你不能在资源中使用try（Java6可能已经几十年不支持了，但谁知道呢），那么你的代码应该是这样的：
Connection connObj = null;
Statement stmt = null;
ResultSet result = null;
try {
// ... do whatever is needed
} finally {
if(result != null) {
try {result.close();} catch (Exception ignored) {}
}
if(stmt != null) {
try {stmt.close();} catch (Exception ignored) {}
}
if(connObj != null) {
try {connObj .close();} catch (Exception ignored) {}
}
}
