proxool池应用

??????02.??编辑web.xml文件，加入下面的语句：

?<servlet>
??<servlet-name>proxool</servlet-name>
??<servlet-class>org.logicalcobwebs.proxool.admin.servlet.AdminServlet</servlet-class>
</servlet>
<servlet-mapping>
??<servlet-name>proxool</servlet-name>
??<url-pattern>/Admin/proxool,./</url-pattern>
</servlet-mapping>

这样你执行执行http://localhost:8080/proxool-test/Admin/proxool,./(?proxool-test?是你的应用名称?)，这样你就可以监控?connection?pooling?的状态了。

????03.??proxool.xml文件的编写：

<?xml?version="1.0"?encoding="ISO-8859-1"?>
<!--?the?proxool?configuration?can?be?embedded?within?your?own?application's.
Anything?outside?the?"proxool"?tag?is?ignored.?-->
<something-else-entirely>
??<proxool>
????<alias>xml-db</alias>
????<driver-url>jdbc:microsoft:sqlserver://localhost:1433;DatabaseName=shop</driver-url>
????<driver-class>com.microsoft.jdbc.sqlserver.SQLServerDriver</driver-class>
????<driver-properties>
??????<property?name="user"?value="sa"/>
??????<property?name="password"?value="sa"/>
????</driver-properties>
????????<!--minimum-connection-count>2</minimum-connection-count-->
????<maximum-active-time>30000</maximum-active-time>
?<maximum-connection-count>100</maximum-connection-count>
?<maximum-connection-lifetime>15000</maximum-connection-lifetime>?<!--?5?hours?-->
??</proxool>
</something-else-entirely>

????04.??要使用这个驱动就要用到2个类，DBConnectionPoolManager.java和Conn.java，Conn.java调用DBConnectionPoolManager.java，

DBConnectionPoolManager.java代码如下：

?import?java.sql.*;
?import?org.logicalcobwebs.proxool.configuration.JAXPConfigurator;
?import?java.io.*;
?
?public?class?DBConnectionPoolManager?{????
?????private?static?DBConnectionPoolManager?dbcpm?=?null;
?????private?Connection?con?=?null;
?????
?????private??DBConnectionPoolManager()?{
????????InputStream?is?=?getClass().getResourceAsStream("/proxool.xml");
????????try{?????????
????????????JAXPConfigurator.configure(new?InputStreamReader(is),?false);
????????????System.out.println("Configuration?file(proxool.xml)?has?been?loaded?!");
????????}catch(Exception?e){?
??????????System.out.println("Load?Configuration?failed?!?"?+?e.getMessage());
??????????????}finally{
??????????????try{?
??????????????????is.close();
???????????????????}catch(Exception?ex){}
??????????????}
?????}
?????static?synchronized?public??DBConnectionPoolManager?getInstance(){
????????if(null==dbcpm)
?????????????dbcpm?=new?DBConnectionPoolManager();
?????????return?dbcpm;
???????}
?????public?Connection?getConnection(){
?????????try{?
?????????????con?=?DriverManager.getConnection("proxool.xml-db");
?????????????}catch(Exception?e){
???????????????????System.out.println("Connection?failed?!?"+e.getMessage());
???????????????}
???????????return?con;
???????}
???
?}?

Conn.java代码如下：

import?java.sql.*;
import?com.dcon.DBConnectionPoolManager;

public?class?Conn
{
?private?DBConnectionPoolManager?dbc?=?null;

?private?Connection?con?=?null;

?private?PreparedStatement?ps?=?null;

?private?Statement?stmt?=?null;

?private?ResultSet?rs?=?null;

?public?Conn()
?{
??dbc?=?DBConnectionPoolManager.getInstance();
?}

?public?PreparedStatement?prepareStatement(String?sql)?throws?SQLException
?{
??try
??{
???con?=?dbc.getConnection();
???ps?=?con.prepareStatement(sql,?ResultSet.TYPE_SCROLL_SENSITIVE,
?????ResultSet.CONCUR_UPDATABLE);
???return?ps;
??}
??catch?(Exception?e)
??{
???e.printStackTrace();
???System.out.println("psDBA?exception?!");
???return?null;
??}
?}

?public?Statement?createStatement()?throws?SQLException
?{
??try
??{
???con?=?dbc.getConnection();
???stmt?=?con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,
?????ResultSet.CONCUR_UPDATABLE);
???return?stmt;
??}
??catch?(Exception?e)
??{
???e.printStackTrace();
???System.out.println("stDBA?exception?!");
???return?null;
??}
?}

?public?ResultSet?resultSet(String?sql)?throws?SQLException
?{
??rs?=?createStatement().executeQuery(sql);
??return?rs;
?}

?public?void?close()
?{
??try
??{
????if(rs!=null)?{rs.close();}
????if(stmt!=null){stmt.close();}
????if(ps!=null)?{ps.close();}
???if?(con?!=?null)
???{
????con.close();
???}
??}
??catch?(Exception?e)
??{
??}
?}
}
使用方法就是使用Conn.java的prepareStatement和createStatement方法。

????03.??使用prepareStatement和createStatement方法一般就是下面这种情况：

???PreparedStatement?ps=dbc.prepareStatement("select?*?from?tt");
???rs=ps.executeQuery();
???while(rs.next())
???{
????Test?test=new?Test();
????test.setId(rs.getInt("id"));
????test.setName(rs.getString("name"));
???}

原来的方法是：

???Statement?st=con.createStatement();
???rs=st.executeQuery("select?*?from?tt");
???while(rs.next())
???{
????Test?test=new?Test();
????test.setId(rs.getInt("id"));
????test.setName(rs.getString("name"));
???}

大家可以参考一下。

????05.??慎用或尽量不要用微软自带的sqlserver的jdbc驱动。在商业应用中，很少有公司真正实用微软的那个什么com.microsoft.jdbc.sqlserver.SQLServerDriver。

????其实发现微软驱动的不足，也是很偶然的机会。在一次移植应用中，系统报告了[Microsoft][SQLServer?JDBC?Driver]ResultSet?can?not?re-read?row?data?for?column之类的错误。为了解决这个错误，跟踪程序忙了大半天，也没有查出问题所在。只能确定在在rs.getString("XXX")的时候必然会出现错误（rs为ResultSet对象）。那么现在就模拟以下当时的环境：
????数据库表：TestTable
????表字段及类型：
?????????guid?char(38)
?????????title?varchar(100)
?????????content?Text
?????????username?varchar(20)
????查询sql语句：
?????????select?guid,username,content,title?from?TestTable?where····
????java代码：
?????????rs.getString("guid");
?????????rs.getBinaryStream("content");
?????????rs.getString("username");
????-----------------------------------------------------------

????上面那段代码，很不荣幸是。使用微软的驱动，必然会报错（就是上面说的那个错误）。如果你跟踪的话，必然是这一行：rs.getString("username")抛出错误。

????那么，如果你把rs.getString("username")和rs.getBinaryStream("content");位置互换以下，会怎么样呢。结果就是可以正常运行。

????为什么会出现这种情况呢，因为微软的驱动，在包含了blob或clob类型（就是Image和Text类型）的字段。那么就必须按照select顺序查询，且不支持重复查询。

（编辑：李大同）

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