我手头有问题，我用spring实现了DAO。其中提取用户对象列表。
我实现了一个callable，它作为任务传递给ExecutorService。 call（）命中数据库以获取用户实体列表。
现在我担心的是：当在ExecutorService线程池中安排此任务时，多个线程同时命中数据库。因此，在20个并发运行的线程之后，我得到了太多与数据库异常的连接。
代码如下：
private class ConsumeCallable implements Callable<WrapperResponse<EntityInterface>> {
private final String userid;
private int minimumRange, maxRange;
// private final AsyncResponse asyncresponse;
private ConsumeCallable(final String entity, int minimumRange, int maxRange) {
this.maxRange = minimumRange;
this.maxRange = maxRange;
this.userid = entity;
}
/** we need to have the parameters set in the task, so creating a wrapper
* */
ConsumeCallable(final String userid, int minimumRange, int maxRange){
this(userid, minimumRange, maxRange);
this.asyncresponse = asyncresponse;
}
/* the wrapper response is set and returned in callable, which is used when we execute the futures*/
@Override
public WrapperResponse<EntityInterface> call() throws Exception
{
List<EntityInterface> listOfEntities = userdao.getUsers(userid, minimumRange, maxRange) ;
return new WrapperResponse (userid, listOfEntities);
}
}
我的DAO类实现如下：
public interface UserDAO {
List<EntityInterface> getUsers(String userid, int minimum, int maximum);
}
public class UserDAOImpl extends JdbcDaoSupport implements UserDAO
{
@Autowired
private DriverManagerDataSource datasource;
@Autowired
private JdbcTemplate jdbcTemplate;
/** here the datasource is autowired from the spring.xml file
* The getUsers() returns a list of other users, however, this will change on future logic
* */
private void setDataSource(DriverManagerDataSource datasource)
{
this.datasource = datasource;
}
@Override
public List<EntityInterface> getUsers(String userid, int minimumRating, int maximumRating) {
if(minimumRating<0 || maximumRating<0 )
throw new ServiceException(new IllegalArgumentException("minimum rating and maximum rating for a user cannot be negative"));
//String query;
String sql = "my sql query";
PreparedStatementSetter ps2 = new PreparedStatementSetter() {
@Override
public void setValues(java.sql.PreparedStatement ps) throws SQLException {
ps.setString(1, userid);
ps.setInt(2, 1);
ps.setString(3, userid);
ps.setInt(4, 1);
//System.out.println(ps.toString());
}
};
List<EntityInterface> users = this.getJdbcTemplate().query(sql,ps2,new RowMapper<EntityInterface>()
{
@Override
public User mapRow(ResultSet rs, int rowNum) throws SQLException
{
User user = new User();
// populate user objects using the user.setter(rs.getString(i));
// return user;
}});
if(users == null)
users = new ArrayList<EntityInterface>();
return users;
}
}
spring.xml如下：
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
xmlns:tx="http://www.springframework.org/schema/tx"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.0.xsd">
<context:component-scan base-package="dao"/>
<context:component-scan base-package="com.crudapp"/>
<!-- Enable Annotation based Declarative Transaction Management -->
<tx:annotation-driven proxy-target-class="true"
transaction-manager="transactionManager" />
<!-- Creating TransactionManager Bean, since JDBC we are creating of type
DataSourceTransactionManager -->
<bean id="transactionManager"
class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
<property name="dataSource" ref="dataSource" />
</bean>
<!-- MySQL DB DataSource -->
<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
<property name="driverClassName" value="com.mysql.jdbc.Driver" />
<property name="url" value="url_string" />
<property name="username" value="username" />
<property name="password" value="password" />
</bean>
<bean id="userDAO" class="crudapproot.dao.UserDAOImpl">
<property name="dataSource" ref="dataSource"></property>
</bean>
<bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
<property name="dataSource" ref="dataSource"/>
</bean>
</beans>