Question

我以编程方式设置连接。

    configuration.setProperty("hibernate.connection.url", "jdbc:mysql://" + host + ":" + port + "/" + dbName);
    LOG.debug("{} Connection URL is jdbc:mysql://{}:{}/{}", Options.TAG, host, port, dbName);
    configuration.setProperty("hibernate.connection.username", user);
    configuration.setProperty("hibernate.connection.password", pass);
    configuration.setProperty("hibernate.c3p0.preferredTestQuery", "SELECT 1");
    configuration.setProperty("hibernate.c3p0.min_size", minConns);
    configuration.setProperty("hibernate.c3p0.max_size", maxConns);
    configuration.setProperty("hibernate.c3p0.max_statements", "50");
    configuration.setProperty("hibernate.connection.driver_class", "com.mysql.jdbc.Driver");
    configuration.setProperty("hibernate.connection.pool_size", "1");
    configuration.setProperty("hibernate.dialect", "org.hibernate.dialect.MySQL5InnoDBDialect");
    configuration.setProperty("hibernate.current_session_context_class", "thread");
    configuration.setProperty("hibernate.cache.provider_class", "org.hibernate.cache.internal.NoCacheProvider");
    configuration.setProperty("hibernate.show_sql", "false");
    configuration.addResource("TransactionBean.hbm.xml");
    ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().applySettings(
            configuration.getProperties()).build();

    sessionFactory = configuration.buildSessionFactory(serviceRegistry);

我收到警告

WARN BasicResourcePool:1851 - com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@6972975c
-- Acquisition Attempt Failed!!! Clearing pending acquires. 
While trying to acquire a needed new resource, we failed to succeed more than the
maximum number of allowed acquisition attempts (30). Last acquisition attempt 
exception: 
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: 
Communications link failure

从配置中可以看出，连接必须按照要求进行测试 configuration.setProperty（＆＃34; hibernate.c3p0.preferredTestQuery＆＃34;，＆＃34; SELECT 1＆＃34;）; 但是它没有经过测试。为什么不查询SELECT 1？

我的目标是在连接尚未建立的情况下获取例外。

Answer 1

哦。如果连接尚未被获得，那么你永远不会看到连接测试失败。客户端将无法从池中检出连接。（我猜想，当我第一次回答时，我错过了令你烦恼的警告。）在进行任何连接测试之前，池中必须有连接。使用testConnectionOnCheckout=true，每个Connection客户端都会看到已经过测试。但这是Connection收购失败的完全不同的问题（上面的警告）

如果您的池无法获取任何连接，则客户端将暂停或超时（如果您已设置checkoutTimeout）。如果池通常获取Connections，但偶尔因某些原因无法使已经获取的Connections无效，那么测试将正常运行，并且将在尝试获取新Connections时通过有时失败。如果失败的采集信号表明DBMS已关闭或不可用，当客户端尝试使用现在已断开的连接时，您将看到此警告和连接测试失败。

Answer 2

您已设置preferredTestQuery，如果将Connections设置为要测试，则会使用testConnectionOnCheckin，但您实际上并未指定任何连接测试。为此，您需要设置testConnectionOnCheckout，idleConnectionTestPeriod和/或{{1}}。请参阅http://www.mchange.com/projects/c3p0/#configuring_connection_testing

未使用configuration.setProperty（＆＃34; hibernate.c3p0.preferredTestQuery＆＃34;，＆＃34; SELECT 1＆＃34;）测试连接;

2 个答案: