为什么 java.sql.DriverManager.getConnection(...) 挂了？
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Why is java.sql.DriverManager.getConnection(...) hanging?
提问by sixtyfootersdude
I am attempting to get a connection to my University's MySQL DB but the connection is hanging.
我正在尝试连接到我大学的 MySQL 数据库，但连接挂起。
import java.sql.*;
public class ConnectToDB {
public static void main(String args[]){
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
String url = "jdbc:mysql://db.cs.myUniversity.com/dbName";
System.out.println("BEFORE");
Connection con = DriverManager.getConnection(url,"me", "password");
System.out.println("AFTER");
...
This call: time java ConnectToDBprints (after I eventually kill it):
这个调用：time java ConnectToDB打印（在我最终杀死它之后）：
Copyright 2004, R.G.Baldwin
BEFORE
AFTER
real 3m9.343s
user 0m0.316s
sys 0m0.027s
I just downloaded MySQL Connector/J from here. I am not sure if that is part of the problem. I followed the directions fairly precisely.
我刚刚从这里下载了 MySQL Connector/J 。我不确定这是否是问题的一部分。我相当精确地遵循了指示。
I can also connect to mysql on the command line like this:
我也可以像这样在命令行上连接到 mysql：
$ mysql -u me -h db.cs.myUniversity.com -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 882328
Server version: 5.0.77 Source distribution
Type 'help;' or '\h' for help. Type '\c' to clear the buffer.
mysql> use dbName;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Database changed
mysql> SHOW tables;
+-------------------+
| Tables_in_dbName |
+-------------------+
| classics |
+-------------------+
1 row in set (0.00 sec)
Possible Problems:
可能的问题：
- The Java code I wrote
- How I installed MySQL Connector/J
- Some kind of network problem blocking the connection
- 我写的Java代码
- 我如何安装 MySQL Connector/J
- 某种网络问题阻止了连接
Question:What should I do to solve this problem? Why is the getConnectioncall hanging?
问题：我应该怎么做才能解决这个问题？为什么getConnection电话挂了？
I was following this tutorial
我正在关注本教程
回答by duffymo
The output you provide is not helpful.
您提供的输出没有帮助。
I see BEFORE and AFTER being printed, so the connection was made. The code doesn't show what those timings encompass, so I can't tell what they mean.
我看到 BEFORE 和 AFTER 被打印，因此建立了连接。代码没有显示这些时间包含的内容，所以我无法说出它们的含义。
If you're suggesting that your code had to killed because the connection was never made, it's probably because your username, password, and client IP have not been GRANTed permissions that are needed.
如果您建议您的代码因从未建立连接而不得不终止，这可能是因为您的用户名、密码和客户端 IP 尚未获得所需的权限。
Could be:
可能：
- your university network; find a network engineer to ask about firewalls.
- permission in the MySQL database; find the DBA and ask.
- your code; you didn't post enough to tell. Post the whole class.
- 你的大学网络；找网络工程师询问防火墙。
- MySQL 数据库中的权限；找到 DBA 并询问。
- 你的代码；你发布的信息不够多。全班发帖。
What's up with that copyright? I'd lose that.
那个版权是怎么回事？我会失去那个。
This code works. Modify it so the pertinent parameters match your problem. (Mine uses MySQL 5.1.51 and a table named Party.) When I run it on my local machine, I get a wall time of 641 ms.
此代码有效。修改它以使相关参数与您的问题相匹配。（我的使用 MySQL 5.1.51 和一个名为 Party 的表。）当我在本地机器上运行它时，我得到 641 毫秒的挂机时间。
package persistence;
import java.sql.*;
import java.util.*;
/**
* DatabaseUtils
* User: Michael
* Date: Aug 17, 2010
* Time: 7:58:02 PM
*/
public class DatabaseUtils
{
/*
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;
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;
}
}
