Tomcat7配连接池可以应用于整个工程、也可以应用于单个应用，前者请看这篇文章
http://blog.csdn.net/caiwenfeng_for_23/article/details/8572616，写的很详细。
后者按下面两步即可，其中数据库连接部分参数及后面的类代码中的一些需要自己根据具体情况修改。如有问题请留言。
1.写context.xml
  在Tomcat的安装文件夹conf下，找到context.xml,加入下面配置，然后文件剪切到工程的META-INF下面。
<Resource name="jdbc/TestDB"
      auth="Container"
      type="javax.sql.DataSource"
      factory="org.apache.tomcat.jdbc.pool.DataSourceFactory"
      testWhileIdle="true"
      testOnBorrow="true"
      testOnReturn="false"
      validationQuery="SELECT 1"
      validationInterval="30000"
      timeBetweenEvictionRunsMillis="30000"
      maxActive="100"
      minIdle="10"
      maxWait="10000"
      initialSize="10"
      removeAbandonedTimeout="60"
      removeAbandoned="true"
      logAbandoned="true"
      minEvictableIdleTimeMillis="30000"
      jmxEnabled="true"
      jdbcInterceptors=
"org.apache.tomcat.jdbc.pool.interceptor.ConnectionState;org.apache.tomcat.jdbc.pool.interceptor.StatementFinalizer"
      username="root"
      password="password"
      driverClassName="com.mysql.jdbc.Driver"
      url="jdbc:mysql://localhost:3306/mysql"/>
2.写个类配置连接池参数,并获取连接查询库。我用的是POSTGRESQL库。保存类后，eclispe里面启动TOMCAT，run as application该类即可。
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;


import org.apache.tomcat.jdbc.pool.DataSource;
import org.apache.tomcat.jdbc.pool.PoolProperties;

public class SimplePOJOExample {

    public static void main(String[] args) throws Exception {
    PoolProperties p = new PoolProperties();
    p.setUrl("jdbc:postgresql://192.168.120.10:7454/dbname");
    p.setDriverClassName("org.postgresql.Driver");
    p.setUsername("user");
    p.setPassword("pwd");
    p.setJmxEnabled(true);
    p.setTestWhileIdle(false);
    p.setTestOnBorrow(true);
    p.setValidationQuery("SELECT 1");
    p.setTestOnReturn(false);
    p.setValidationInterval(30000);
    p.setTimeBetweenEvictionRunsMillis(30000);
    p.setMaxActive(100);
    p.setInitialSize(10);
    p.setMaxWait(10000);
    p.setRemoveAbandonedTimeout(60);
    p.setMinEvictableIdleTimeMillis(30000);
    p.setMinIdle(10);
    p.setLogAbandoned(true);
    p.setRemoveAbandoned(true);
    p.setJdbcInterceptors("org.apache.tomcat.jdbc.pool.interceptor.ConnectionState;"+
      "org.apache.tomcat.jdbc.pool.interceptor.StatementFinalizer");
    DataSource datasource = new DataSource();
    datasource.setPoolProperties(p);

    Connection con = null;
    try {
      con = datasource.getConnection();
      Statement st = con.createStatement();
      ResultSet rs = st.executeQuery("select 1 from table where c1='123'");
      int cnt = 1;
      while (rs.next()) {
      System.out.println(rs.getString(1));
      }
      rs.close();
      st.close();
    } finally {
      if (con!=null) try {con.close();}catch (Exception ignore) {}
    }
    }

}