Java MySQL 连接池不工作 [英] Java MySQL connetion pool is not working
问题描述
我用 Java 编写了一个运行 MySQL 查询并返回结果的函数.我在这里使用这种方法实现了连接池:http://www.kodejava.org/how-do-i-create-a-database-connection-pool/.该函数正在工作，但连接时间仍然与没有池时相同~190 毫秒.有人能告诉我我做错了什么吗?
I've written a function in Java that runs a MySQL query and returns results. I've implemented connection pooling using this method here: http://www.kodejava.org/how-do-i-create-a-database-connection-pool/. The function is working, but connection time is still the same as it was without pooling ~190 ms. Can somebody tell me what am I doing wrong?
这是我的代码:
public static ArrayList<Map<String,Object>> query(String q) throws Exception {
long start, end;
GenericObjectPool connectionPool = null;
String DRIVER = "com.mysql.jdbc.Driver";
String URL = "jdbc:mysql://localhost/dbname";
String USER = "root";
String PASS = "";
Class.forName(DRIVER).newInstance();
connectionPool = new GenericObjectPool();
connectionPool.setMaxActive(10);
ConnectionFactory cf = new DriverManagerConnectionFactory(URL, USER, PASS);
PoolableConnectionFactory pcf = new PoolableConnectionFactory(cf, connectionPool, null, null, false, true);
DataSource ds = new PoolingDataSource(connectionPool);
//create statement
Statement Stm = null;
try {
Connection Con = null;
PreparedStatement stmt = null;
start = System.currentTimeMillis();
Con = ds.getConnection();
end = System.currentTimeMillis();
System.out.println("DB Connection: " + Long.toString(end - start) + " ms");
//fetch out rows
ArrayList<Map<String, Object>> Rows = new ArrayList<Map<String,Object>>();
Stm = Con.createStatement();
//query
ResultSet Result = null;
boolean Returning_Rows = Stm.execute(q);
if (Returning_Rows) {
Result = Stm.getResultSet();
} else {
return new ArrayList<Map<String,Object>>();
}
//get metadata
ResultSetMetaData Meta = null;
Meta = Result.getMetaData();
//get column names
int Col_Count = Meta.getColumnCount();
ArrayList<String> Cols = new ArrayList<String>();
for (int Index=1; Index<=Col_Count; Index++) {
Cols.add(Meta.getColumnName(Index));
}
while (Result.next()) {
HashMap<String,Object> Row = new HashMap<String,Object>();
for (String Col_Name:Cols) {
Object Val = Result.getObject(Col_Name);
Row.put(Col_Name,Val);
}
Rows.add(Row);
}
//close statement
Stm.close();
//pass back rows
return Rows;
} catch (Exception Ex) {
System.out.print(Ex.getMessage());
return new ArrayList<Map<String,Object>>();
} finally {
if (Stm != null) {
Stm.close();
}
if (Stm != null) {
Stm.close();
}
System.out.println("Max connections: " + connectionPool.getMaxActive());
System.out.println("Active connections: " + connectionPool.getNumActive());
System.out.println("Idle connections: " + connectionPool.getNumIdle());
}
}
这是每次控制台输出:
DB Connection: 186 ms
Max connections: 10
Active connections: 1
Idle connections: 0
更新: 我应该注意，使用它的 Java 应用程序是这样工作的:执行，只运行一个查询并关闭.我想如果 PHP 像这样工作并且它默认使用连接池，那么 Java 也应该这样吗?如果我错了，请纠正我.
UPDATE: I should note, that Java application that uses this works like this: executes, only runs one query and closes. I figured if PHP works like this and it's using connection pooling by default, so should Java? Correct me if I'm wrong.
推荐答案
您创建了一个连接池，但您没有将任何内容放入其中.您的连接池在创建时是空的，因此您对它的第一个请求肯定会创建一个新连接，并且与手动获取连接一样慢.
You create a connection pool, but you don't put anything into it. You connection pool is empty when it is created, so your first request to it is guaranteed to to create a new connection and will be just as slow as getting a connection manually.
尝试将您的代码放入一个循环中，在该循环中您反复从池中获得一个连接.尝试一次，五次，十次和十五次.请注意结果如何变化.
Try putting your code into a loop, where you repeatedly get a connection from the pool. Try it once, five times, ten times and fifteen times. Note how the results change.
某些连接池支持自动创建和保持最小数量的连接可供使用以及最大.当池初始化时，它将预取连接，因此前几次调用不会延迟.
Some connection pools support automatically creating and holding a minimum number of connections ready for use as well as a maximum. When the pool is initialised it will pre-fetch connections so the first few calls aren't delayed.
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