C3P0是一个开源的JDBC连接池。

在Spring中,C3P0的一些配置,介绍如下(只列了一部分,不是全部)

<!-- c3p0连接池配置 -->
     <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
          <!-- 用户名-->
          <property name="user" value="${username}"/>
          <!-- 用户密码-->
          <property name="password" value="${password}"/>
          <property name="driverClass" value="${driver_class}"/>
          <property name="jdbcUrl" value="${url}"/>

           <!--连接池中保留的最大连接数。默认值: 15 --> 
          <property name="maxPoolSize" value="20"/>
          <!-- 连接池中保留的最小连接数,默认为:3-->
          <property name="minPoolSize" value="2"/>
          <!-- 初始化连接池中的连接数,取值应在minPoolSize与maxPoolSize之间,默认为3-->
          <property name="initialPoolSize" value="2"/>

          <!--最大空闲时间,60秒内未使用则连接被丢弃。若为0则永不丢弃。默认值: 0 --> 
          <property name="maxIdleTime">60</property>
          
          <!-- 当连接池连接耗尽时,客户端调用getConnection()后等待获取新连接的时间,超时后将抛出SQLException,如设为0则无限期等待。单位毫秒。默认: 0 --> 
          <property name="checkoutTimeout" value="3000"/>
          
          <!--当连接池中的连接耗尽的时候c3p0一次同时获取的连接数。默认值: 3 --> 
          <property name="acquireIncrement" value="2"/>

         <!--定义在从数据库获取新连接失败后重复尝试的次数。默认值: 30 ;小于等于0表示无限次--> 
          <property name="acquireRetryAttempts" value="0"/>

          <!--重新尝试的时间间隔,默认为:1000毫秒--> 
          <property name="acquireRetryDelay" value="1000" />

          <!--关闭连接时,是否提交未提交的事务,默认为false,即关闭连接,回滚未提交的事务 --> 
          <property name="autoCommitOnClose">false</property>

          <!--c3p0将建一张名为Test的空表,并使用其自带的查询语句进行测试。如果定义了这个参数那么属性preferredTestQuery将被忽略。你不能在这张Test表上进行任何操作,它将只供c3p0测试使用。默认值: null --> 
          <property name="automaticTestTable">Test</property>

          <!--如果为false,则获取连接失败将会引起所有等待连接池来获取连接的线程抛出异常,但是数据源仍有效保留,并在下次调用getConnection()的时候继续尝试获取连接。如果设为true,那么在尝试获取连接失败后该数据源将申明已断开并永久关闭。默认: false--> 
          <property name="breakAfterAcquireFailure">false</property>

          <!--每60秒检查所有连接池中的空闲连接。默认值: 0,不检查 --> 
          <property name="idleConnectionTestPeriod">60</property>
          <!--c3p0全局的PreparedStatements缓存的大小。如果maxStatements与maxStatementsPerConnection均为0,则缓存不生效,只要有一个不为0,则语句的缓存就能生效。如果默认值: 0--> 
          <property name="maxStatements">100</property>
          <!--maxStatementsPerConnection定义了连接池内单个连接所拥有的最大缓存statements数。默认值: 0 --> 
          <property name="maxStatementsPerConnection"></property>
     </bean>

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C3P0更详细的配置项及其含义,请参考:http://www.mchange.com/projects/c3p0/index.html,部分内容摘录如下:

acquireIncrement
acquireRetryAttempts
acquireRetryDelay
autoCommitOnClose
automaticTestTable
breakAfterAcquireFailure
checkoutTimeout
connectionCustomizerClassName
connectionTesterClassName
debugUnreturnedConnectionStackTraces
factoryClassLocation
forceIgnoreUnresolvedTransactions
idleConnectionTestPeriod
initialPoolSize
maxAdministrativeTaskTime
maxConnectionAge
maxIdleTime
maxIdleTimeExcessConnections
maxPoolSize
maxStatements
maxStatementsPerConnection
minPoolSize
numHelperThreads
overrideDefaultUser
overrideDefaultPassword
password
preferredTestQuery
propertyCycle
testConnectionOnCheckin
testConnectionOnCheckout
unreturnedConnectionTimeout
user
usesTraditionalReflectiveProxies
acquireIncrement
Default: 3

acquireRetryAttempts

Default: 30

acquireRetryDelay

Default: 1000

autoCommitOnClose

Default: false

automaticTestTable

Default: null

breakAfterAcquireFailure

Default: false

checkoutTimeout

Default: 0
The number of milliseconds a client calling getConnection() will wait for a Connection to be checked-in or acquired when the pool is exhausted. Zero means wait indefinitely. Setting any positive value will cause the getConnection() call to time-out and break with an 
SQLException after the specified number of milliseconds.


connectionCustomizerClassName

Default: null
The fully qualified class-name of an implememtation of the 
ConnectionCustomizer interface, which users can implement to set up Connections when they are acquired from the database, or on check-out, and potentially to clean things up on check-in and Connection destruction. If standard Connection properties (holdability, readOnly, or transactionIsolation) are set in the ConnectionCustomizer’s onAcquire() method, these will override the Connection default values.

connectionTesterClassName

Default: com.mchange.v2.c3p0.impl.DefaultConnectionTester
The fully qualified class-name of an implememtation of the 
ConnectionTester interface, or 
QueryConnectionTester if you would like instances to have access to a user-configured 
preferredTestQuery. This can be used to customize how c3p0 DataSources test Connections, but with the introduction of 
automaticTestTable and 
preferredTestQuery configuration parameters, “rolling your own” should be overkill for most users. [See 
“Configuring Connection Testing”]

debugUnreturnedConnectionStackTraces

Default: false
If true, and if 
unreturnedConnectionTimeout is set to a positive value, then the pool will capture the stack trace (via an Exception) of all Connection checkouts, and the stack traces will be printed when unreturned checked-out Connections timeout. This is intended to debug applications with Connection leaks, that is applications that occasionally fail to return Connections, leading to pool growth, and eventually exhaustion (when the pool hits 
maxPoolSize with all Connections checked-out and lost). This parameter should only be set while debugging, as capturing the stack trace will slow down every Connection check-out.
Does Not Support Per-User Overrides.

factoryClassLocation

Default: null
DataSources that will be bound by JNDI and use that API’s Referenceable interface to store themselves may specify a URL from which the class capable of dereferencing a them may be loaded. If (as is usually the case) the c3p0 libraries will be locally available to the JNDI service, leave this set as null.
Does Not Support Per-User Overrides.


forceIgnoreUnresolvedTransactions

Default: false

idleConnectionTestPeriod

Default: 0

initialPoolSize

Default: 3

maxAdministrativeTaskTime

Default: 0
Seconds before c3p0’s thread pool will try to interrupt an apparently hung task. Rarely useful. Many of c3p0’s functions are not performed by client threads, but asynchronously by an internal thread pool. c3p0’s asynchrony enhances client performance directly, and minimizes the length of time that critical locks are held by ensuring that slow jdbc operations are performed in non-lock-holding threads. If, however, some of these tasks “hang”, that is they neither succeed nor fail with an Exception for a prolonged period of time, c3p0’s thread pool can become exhausted and administrative tasks backed up. If the tasks are simply slow, the best way to resolve the problem is to increase the number of threads, via 
numHelperThreads. But if tasks sometimes hang indefinitely, you can use this parameter to force a call to the task thread’s 
interrupt() method if a task exceeds a set time limit. [c3p0 will eventually recover from hung tasks anyway by signalling an “APPARENT DEADLOCK” (you’ll see it as a warning in the logs), replacing the thread pool task threads, and interrupt()ing the original threads. But letting the pool go into APPARENT DEADLOCK and then recover means that for some periods, c3p0’s performance will be impaired. So if you’re seeing these messages, increasing 
numHelperThreads and setting 
maxAdministrativeTaskTime might help.
maxAdministrativeTaskTime should be large enough that any resonable attempt to acquire a Connection from the database, to test a Connection, or two destroy a Connection, would be expected to succeed or fail within the time set. Zero (the default) means tasks are never interrupted, which is the best and safest policy under most circumstances. If tasks are just slow, allocate more threads. If tasks are hanging forever, try to figure out why, and maybe setting 
maxAdministrativeTaskTime can help in the meantime.
Does Not Support Per-User Overrides.

maxConnectionAge

Default: 0
Seconds, effectively a time to live. A Connection older than 
maxConnectionAge will be destroyed and purged from the pool. This differs from 
maxIdleTime in that it refers to absolute age. Even a Connection which has not been much idle will be purged from the pool if it exceeds 
maxConnectionAge. Zero means no maximum absolute age is enforced.


maxIdleTime

Default: 0

maxIdleTimeExcessConnections

Default: 0
Number of seconds that Connections in excess of 
minPoolSize should be permitted to remain idle in the pool before being culled. Intended for applications that wish to aggressively minimize the number of open Connections, shrinking the pool back towards minPoolSize if, following a spike, the load level diminishes and Connections acquired are no longer needed. If 
maxIdleTime is set,
maxIdleTimeExcessConnections should be smaller if the parameter is to have any effect. Zero means no enforcement, excess Connections are not idled out.


maxPoolSize

Default: 15

maxStatements

Default: 0

maxStatementsPerConnection

Default: 0

minPoolSize

Default: 3

numHelperThreads

Default: 3
c3p0 is very asynchronous. Slow JDBC operations are generally performed by helper threads that don’t hold contended locks. Spreading these operations over multiple threads can significantly improve performance by allowing multiple operations to be performed simultaneously.
Does Not Support Per-User Overrides.


overrideDefaultUser

Default: null
Does Not Support Per-User Overrides.

overrideDefaultPassword

Default: null
Does Not Support Per-User Overrides.

password

Default: null
Does Not Support Per-User Overrides.

preferredTestQuery

Default: null
Defines the query that will be executed for all connection tests, if the default ConnectionTester (or some other implementation of 
QueryConnectionTester, or better yet 
FullQueryConnectionTester) is being used. Defining a 
preferredTestQuery that will execute quickly in your database may dramatically speed up Connection tests. (If no 
preferredTestQuery is set, the default ConnectionTester executes a 
getTables() call on the Connection’s DatabaseMetaData. Depending on your database, this may execute more slowly than a “normal” database query.) 
NOTE: The table against which your preferredTestQuery will be run must exist in the database schema prior to your initialization of your DataSource. If your application defines its own schema, tryautomaticTestTable instead. [See 
“Configuring Connection Testing”]

propertyCycle

Default: 0

testConnectionOnCheckin

Default: false

testConnectionOnCheckout

Default: false

unreturnedConnectionTimeout

Default: 0
Seconds. If set, if an application checks out but then fails to check-in [i.e. close()] a Connection within the specified period of time, the pool will unceremoniously destroy() the Connection. This permits applications with occasional Connection leaks to survive, rather than eventually exhausting the Connection pool. And that’s a shame. Zero means no timeout, applications are expected to close() their own Connections. Obviously, if a non-zero value is set, it should be to a value longer than any Connection should reasonably be checked-out. Otherwise, the pool will occasionally kill Connections in active use, which is bad. 
This is basically a bad idea, but it’s a commonly requested feature. Fix your $%!@% applications so they don’t leak Connections! Use this temporarily in combination with debugUnreturnedConnectionStackTraces to figure out where Connections are being checked-out that don’t make it back into the pool!


user

Default: null
Does Not Support Per-User Overrides.

usesTraditionalReflectiveProxies

Default: false
c3p0 originally used reflective dynamic proxies for implementations of Connections and other JDBC interfaces. As of c3p0-0.8.5, non-reflective, code-generated implementations are used instead. As this was a major change, and the old codebase had been extensively used and tested, this parameter was added to allow users to revert of they had problems. The new, non-reflexive implementation is faster, and has now been widely deployed and tested, so it is unlikely that this parameter will be useful. Both the old reflective and newer non-reflective codebases are being maintained, but support for the older codebase may (or may not) be dropped in the future.

=======================================================================================================================

一个task应用数据库连接配置的例子:

<bean id="dataSource" class="org.springframework.beans.factory.config.MethodInvokingFactoryBean"> 
	      <property name="staticMethod">
	          <value>com.mchange.v2.c3p0.DataSources.pooledDataSource</value>
	      </property>
	      <property name="arguments">
		      <list>
	          	<ref local="olpsUnpooledDataSource"/>
	            	<props>
						<prop key="acquireIncrement">1</prop>
						<prop key="initialPoolSize">1</prop>
						<prop key="minPoolSize">1</prop>
						<prop key="maxPoolSize">5</prop>
						<prop key="maxIdleTime">1800</prop>
						<prop key="maxIdleTimeExcessConnections">1000</prop> <!-- 自动收缩连接用的,单位秒-->
						<!-- 自动重连需要的三个参数  -->
						<prop key="acquireRetryAttempts">30</prop>
						<prop key="acquireRetryDelay">1000</prop>
						<prop key="breakAfterAcquireFailure">false</prop>
						<!-- 获取一个connection需要的时间,单位毫秒 -->
						<prop key="checkoutTimeout">500</prop>
					</props>
      		</list>
  		</property>
	</bean>
	   
	<bean id="olpsUnpooledDataSource" class="com.mchange.v2.c3p0.DriverManagerDataSource"> 
		<property name="driverClass">
            <value>com.alibaba.china.jdbc.SimpleDriver</value>
        </property>
        <property name="jdbcUrl">
            <value>${database.driver.url}</value>
        </property>
        <property name="properties">
			<bean class="com.alibaba.china.biz.common.security.SecureIdentityLoginModule">
                <property name="user"><value>${username}</value></property>
                <property name="password"><value>${password}</value></property>
                <property name="bigStringTryClob"><value>true</value></property>
                <property name="clientEncoding"><value>GBK</value></property>
                <property name="serverEncoding"><value>ISO-8859-1</value></property>
            </bean>
        </property>
    </bean>


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原文链接:https://blog.csdn.net/caihaijiang/article/details/6843496