标签: connection-pooling

需要代码在java中创建连接池吗？我们如何确保连接池不返回已在使用的同一对象？如果客户端从连接池中取出连接后关闭连接会怎么样？

更新1:

我想用简单的Java术语创建它,并希望看到它在多线程环境中如何工作.我的意思是哪些方法将同步,哪些方法不同步.这门课还会成为公共课吗？如果是,则任何人都可以访问此类并重新初始化连接池？

更新2:

我有一些代码如下.但我不知道如何"关闭来自池的连接将其返回到池中,它不会在物理上关闭连接." 此外,我没有理解这一点"因为如果连接已从池中借用而尚未返回,则它不是"可用"且无法重新分配给池中的另一个客户端.

import java.util.*;
import java.sql.*;

class ConnectionPoolManager
{

 String databaseUrl = "jdbc:mysql://localhost:3306/myDatabase";
 String userName = "userName";
 String password = "userPass";

 Vector connectionPool = new Vector();

 public ConnectionPoolManager()
 {
  initialize();
 }

 public ConnectionPoolManager(
  //String databaseName,
  String databaseUrl,
  String userName,
  String password
  )
 {
  this.databaseUrl = databaseUrl;
  this.userName = userName;
  this.password = password;
  initialize();
 }

 private void initialize()
 {
  //Here we can initialize all the information that we need
  initializeConnectionPool();
 }

 private void initializeConnectionPool()
 {
  while(!checkIfConnectionPoolIsFull())
  { …

org.apache.commons.dbcp BasicDatasource和PoolingDataSoure有什么区别？两者都支持连接池吗？什么时候使用它们？

以下是我的帮助类获取数据库连接:

我已经使用了这里描述的C3P0连接池.

public class DBConnection {

    private static DataSource dataSource;
    private static final String DRIVER_NAME;
    private static final String URL;
    private static final String UNAME;
    private static final String PWD;

    static {

        final ResourceBundle config = ResourceBundle
                .getBundle("props.database");
        DRIVER_NAME = config.getString("driverName");
        URL = config.getString("url");
        UNAME = config.getString("uname");
        PWD = config.getString("pwd");

        dataSource = setupDataSource();
    }

    public static Connection getOracleConnection() throws SQLException {
        return dataSource.getConnection();
    }

    private static DataSource setupDataSource() {
        ComboPooledDataSource cpds = new ComboPooledDataSource();
        try {
            cpds.setDriverClass(DRIVER_NAME);
        } …

我正在使用Celery独立版(不在Django中).我计划在多台物理机上运行一个工作任务类型.该任务执行以下操作

1. 接受XML文档.
2. 改变它.
3. 进行多个数据库读写操作.

我正在使用PostgreSQL,但这同样适用于使用连接的其他商店类型.过去,我使用数据库连接池来避免在每个请求上创建新的数据库连接,或者避免将连接打开太长时间.但是,由于每个Celery工作程序都在一个单独的进程中运行,我不确定它们实际上是如何共享池的.我错过了什么吗？我知道Celery允许你坚持从芹菜工人那里得到的结果,但这不是我想在这里做的.每个任务可以根据处理的数据执行多个不同的更新或插入.

从Celery工作者访问数据库的正确方法是什么？

是否可以跨多个工作人员/任务共享一个池,还是有其他方法可以做到这一点？

我试图确定我是否实际使用JDBC连接池.经过一些研究,实施几乎看起来太容易了.事实上比常规连接更容易,所以我想验证.

这是我的连接类:

public class DatabaseConnection {

Connection conn = null;

public Connection getConnection() {

    BasicDataSource bds = new BasicDataSource();
    bds.setDriverClassName("com.mysql.jdbc.Driver");
    bds.setUrl("jdbc:mysql://localhost:3306/data");
    bds.setUsername("USERNAME");
    bds.setPassword("PASSWORD");

    try{
        System.out.println("Attempting Database Connection");
        conn = bds.getConnection();
        System.out.println("Connected Successfully");
    }catch(SQLException e){
        System.out.println("Caught SQL Exception: " + e);
    }
    return conn;
}

public void closeConnection() throws SQLException {
    conn.close();
}

}

这是真正的连接汇集吗？我在另一个类中使用连接如下:

        //Check data against database.
    DatabaseConnection dbConn = new DatabaseConnection();
    Connection conn;
    ResultSet rs;
    PreparedStatement prepStmt;

    //Query database and check username/pass against table.
    try{
        conn = dbConn.getConnection(); …

我正在Eclipse Juno中开发Java EE Web应用程序.我已将Tomcat配置为使用JDBC连接池(org.apache.tomcat.jdbc.pool)以及PostgreSQL数据库.以下是我的项目的META-INF/context.xml中的配置:

<?xml version="1.0" encoding="UTF-8"?>
<Context>
    <!-- Configuration for the Tomcat JDBC Connection Pool -->
    <Resource name="jdbc/someDB"
        type="javax.sql.DataSource"
        auth="Container"
        factory="org.apache.tomcat.jdbc.pool.DataSourceFactory"
        driverClassName="org.postgresql.Driver"
        url="jdbc:postgresql://localhost:5432/somedb"
        username="postgres"
        password="12345"
        maxActive="100"
        minIdle="10"
        initialSize="10"
        validationQuery="SELECT 1"
        validationInterval="30000"
        removeAbandoned="true"
        removeAbandonedTimeout="60"
        abandonWhenPercentageFull="50" />
</Context>

我的应用程序使用Eclipse部署到Tomcat,在Tomcat的context.xml中,属性reloadable设置为"true",以便在检测到更改时自动重新加载Web应用程序:

<Context reloadable="true">

我注意到,每次上面提到的自动重新加载时,都会保留10个与PostgreSQL db的连接(因为在webapp的context.xml中,initialSize ="10").因此,在10次更改后抛出PSQLException:

org.postgresql.util.PSQLException: FATAL: sorry, too many clients already
...

如果我手动重启Tomcat - 一切都很好,只保留10个连接.

有没有人知道解决这个问题的方法,所以有可能将reloadable设置为"true"并且不会在每次重新加载上下文时导致更多连接汇集？

非常感谢任何帮助.

PS Apache Tomcat版本7.0.32

我在Tomcat中使用C3P0作为连接池,我看到非常令人担忧的错误:

2010-09-16 13:25:00,160 [Timer-0] WARN  com.mchange.v2.async.ThreadPoolAsynchronousRunner  - com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@43502400 -- APPARENT DEADLOCK!!! Creating emergency threads for unassigned pending tasks!
2010-09-16 13:25:01,407 [Timer-0] WARN  com.mchange.v2.async.ThreadPoolAsynchronousRunner  - com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@43502400 -- APPARENT DEADLOCK!!! Complete Status:
  Managed Threads: 10
  Active Threads: 0
  Active Tasks:
  Pending Tasks:
    com.mchange.v2.resourcepool.BasicResourcePool$1RefurbishCheckinResourceTask@6e4151a7
  Pool thread stack traces:
  Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#6,5,main]
    java.lang.Object.wait(Native Method)
    com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:534)
  Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#2,5,main]
    java.lang.Object.wait(Native Method)
    com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:534)
  Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#1,5,main]
    java.lang.Object.wait(Native Method)
    com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:534)
  Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#0,5,main]
    java.lang.Object.wait(Native Method)
    com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:534)
  Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#5,5,main]
    java.lang.Object.wait(Native Method)
    com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:534)
  Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#4,5,main]
    java.lang.Object.wait(Native Method)

... many more, exact same stack trace

第534行是:

 while (true) {
   Runnable …

大家好我正在使用Hibernate + Struts2 + Tomcat6 + Mysql作为我的J2EE框架.我一直在使用hibernate的内置连接池机制,但结果证明mysql在8小时后关闭它的连接是有问题的.无论如何,我google了一下,发现我应该通过JNDI数据源获得我的连接,但我无法就此达成一个完整的教程.我应该采取什么措施呢？请给我足够的细节,我对此有点新意.这是我的hibernate.cfg.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
  <session-factory>

    <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
    <property name="hibernate.connection.url">
            jdbc:mysql://localhost/hposg?characterEncoding=UTF-8
    </property>
    <property name="connection.username">root</property>
    <property name="connection.password"></property>
    <property name="show_sql">true</property>
    <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
    <property name="current_session_context_class">thread</property>
    <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>
    <property name="hbm2ddl.auto">update</property>

    <property name="hibernate.max_fetch_depth">3</property>

    <property name="hibernate.connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</property>
    <property name="hibernate.c3p0.acquire_increment">2</property>
    <property name="hibernate.c3p0.idle_test_period">300</property>
    <property name="hibernate.c3p0.timeout">1800</property>
    <property name="hibernate.c3p0.max_size">25</property>
    <property name="hibernate.c3p0.min_size" >3</property>
    <property name="hibernate.c3p0.max_statement">0</property>
    <property name="hibernate.c3p0.preferredTestQuery">select 1;</property>
    <property name="hibernate.c3p0.testConnectionOnCheckout">true</property>
    <property name="hibernate.c3p0.validate">true</property>

      <!-- Mapping files -->

      <mapping resource="com/hposg/hibernate/resources/Player.hbm.xml"/>
      <mapping resource="com/hposg/hibernate/resources/Game.hbm.xml"/>
      ...

  </session-factory>
</hibernate-configuration>

我也尝试了这个,但它没有成功:在WebContent/META-INF中创建一个context.xml,包含:

<Context path="" docBase="../RSGames" debug="0" …

我已经在可怕的"错误19"上尝试了所有其他帖子,并发现少数答案不适用或没有帮助,因此这篇新帖子.对于所有Azure + EF用户来说,这是一个非常严重的潜在问题.

第一次出现:

我正在使用VS2013 EF6.1 Razor项目中的所有内容的最新版本(最后列出的软件包).该数据库托管在SQL Azure上.

运行我的webapp几次后(在开发环境中)我收到此错误: A transport-level error has occurred when receiving results from the server. (provider: Session Provider, error: 19 - Physical connection is not usable)

它死的线总是如此:

我收集错误与连接池(和连接用完)有关,但我无法在任何地方发现泄漏.

当我访问整个应用程序中的OWIN成员资格和其他数据库功能时,我有一个DatabaseContoller所有其他控制器继承的.这将创建所有相关组件并处理它们.

DatabaseController.cs

[Authorize]
public class DatabaseController : Controller
{
    #region properties
    /// <summary>
    /// User manager - attached to application DB context
    /// </summary>
    protected UserManager<ApplicationUser> UserManager { get; set; }

    /// <summary>
    /// Role manager - attached to application DB context
    /// </summary>
    protected …

所以我已经弄清楚了我的错误,现在我只是在寻找一些关于究竟发生了什么的见解.我正在使用Apache Tomcat版本7.0.32.我正在使用本教程为JDBC设置池.在我的META-INF文件夹中,我创建了一个context.xml文件并将其放在那里.

<?xml version="1.0" encoding="UTF-8"?>

<Context>
    <Resource type="javax.sql.DataSource" name="jdbc/gmustudent"
        factory="org.apache.tomcat.jdbc.pool.DataSourceFactory" 
        driverClassName="com.mysql.jdbc.Driver"
        url="jdbc:mysql://localhost:3306/official"
        username="root" password="root"
        maxActive="100" maxIdle="20" minIdle="15" initialSize="15" maxWait="10000" />
</Context>

我写这篇文章时遇到了这个错误

WARNING: Unexpected exception resolving reference
java.sql.SQLException: com.mysql.jdbc.Driver
    at org.apache.tomcat.jdbc.pool.PooledConnection.connectUsingDriver(PooledConnection.java:254)
    at org.apache.tomcat.jdbc.pool.PooledConnection.connect(PooledConnection.java:182)
    at org.apache.tomcat.jdbc.pool.ConnectionPool.createConnection(ConnectionPool.java:699)
    at org.apache.tomcat.jdbc.pool.ConnectionPool.borrowConnection(ConnectionPool.java:631)
    at org.apache.tomcat.jdbc.pool.ConnectionPool.init(ConnectionPool.java:485)
    at org.apache.tomcat.jdbc.pool.ConnectionPool.<init>(ConnectionPool.java:143)
    at org.apache.tomcat.jdbc.pool.DataSourceProxy.pCreatePool(DataSourceProxy.java:116)
    at org.apache.tomcat.jdbc.pool.DataSourceProxy.createPool(DataSourceProxy.java:103)
    at org.apache.tomcat.jdbc.pool.DataSourceFactory.createDataSource(DataSourceFactory.java:539)
    at org.apache.tomcat.jdbc.pool.DataSourceFactory.getObjectInstance(DataSourceFactory.java:237)
    at org.apache.naming.factory.ResourceFactory.getObjectInstance(ResourceFactory.java:143)
    at javax.naming.spi.NamingManager.getObjectInstance(NamingManager.java:304)
    at org.apache.naming.NamingContext.lookup(NamingContext.java:843)
    at org.apache.naming.NamingContext.lookup(NamingContext.java:154)
    at org.apache.naming.NamingContext.lookup(NamingContext.java:831)
    at org.apache.naming.NamingContext.lookup(NamingContext.java:168)
    at org.apache.catalina.core.NamingContextListener.addResource(NamingContextListener.java:1061)
    at org.apache.catalina.core.NamingContextListener.createNamingContext(NamingContextListener.java:671)
    at org.apache.catalina.core.NamingContextListener.lifecycleEvent(NamingContextListener.java:270)
    at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
    at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5173)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1559)
    at …