Java Learning Note-c3p0 connection pooling and meta data Analysis (42)

First step: Import the C3P0 package

Step two: Under the Classpath directory, create a C3p0-config.xml

<?xml version="1.0" encoding="UTF-8"?>

<c3p0-config>

<!--default configuration, can only occur once--

<default-config>

<!--connection Timeout setting 30 seconds--

<property name="Checkouttimeout">30000</property>

<!--30 seconds to check connection's free--

<property name="Idleconnectiontestperiod">30</property>

<!--initialized Pool size--

<property name="initialpoolsize">2</property>

<!--up to one connection idle time-

<property name="MaxIdleTime">30</property>

<!--up to how many connections connection

<property name="maxpoolsize">10</property>

< A few connections in the pool with!--minimum

<property name="minpoolsize">2</property>

<!--batch-processed statements

-

<property name="maxstatements">50</property>

<!--a few connections per increase

<property name="acquireincrement">3</property>

<property name="Driverclass">com.mysql.jdbc.Driver</property>

<property name="Jdbcurl">

<! [cdata[jdbc:mysql://127.0.0.1:3306/db909?useunicode=true&characterencoding=utf-8]]>

</property>

<property name="user">root</property>

<property name="password">1234</property>

</default-config>

</c3p0-config>

Step three: Create a factory class to get this connection

Package cn.itcast.utils;

import java.sql.Connection;

import Javax.sql.DataSource;

import Com.mchange.v2.c3p0.ComboPooledDataSource;

Public class datasourceutils {

Private Static DataSource DS;

Static {

ds =//default configuration in Read C3p0-config.xml

New Combopooleddatasource ();

}

Public Static DataSource Getdatassource () {

return DS;

}

Public Static Connection Getconn () {

Connection con = null;

Try {

con = ds. getconnection ();//each time a new connection is obtained from the DS

}catch(Exception e) {

E.printstacktrace ();

}

return con;

}

}

Combopooleddatasource has three constructs:

With no parameters.

Receives a Boolean

By default, True, that is, all connection.autocommit properties are true.

That receives a string of

In a c3p0-config.xml file, you can configure multiple connections. In addition to the default connection, the others are called named Connections. Pass

<named-config name= "xxxx"/>

Specify a named connection:

<!--default configuration, can only occur once--

<named-config name="db909">

<property name="Checkouttimeout">1000</property>

<property name="Idleconnectiontestperiod">30</property>

<property name="initialpoolsize">2</property>

<property name="MaxIdleTime">30</property>

<property name="maxpoolsize">5</property>

<property name="minpoolsize">2</property>

<property name="maxstatements">50</property>

<property name="acquireincrement">3</property>

<property name="Driverclass">com.mysql.jdbc.Driver</property>

<property name="Jdbcurl">

<! [cdata[jdbc:mysql://127.0.0.1:3306/db909?useunicode=true&characterencoding=utf-8]]>

</property>

<property name="user">root</property>

<property name="password">1234</property>

</named-config>

Connect to the database through a named connection in your code:

ds =

New Combopooleddatasource ("db909");

Summarize:

C3p0 The connection pool, the connection is wrapped only when the user obtains the connection.

Meta Data analysis

metadata, which is the analysis of all the information in a database, is the case where only one object is owned by connection.

Databasemetadate-describes the database information.

Resultsetmetadate-The type information that describes the result of the data. Core.

If you want to perform meta-data analysis, you must use Statement,preparedstatement.

list<map> list = Run.query ("SELECT * from users", New Maplisthandler ());

[{id= "U001", name= "Jack", pwd= "ddd"} ....]

list<bean> list = Run.query ("SELECT * from users", New Beanlisthanderl<user> (User.class));

[USER=[ID=DD],,,,,]

Exports all the tables and data from a specified database to Excel.

CREATE VIEW UC As

SELECT u.name as uname,c.name as CNAME

From the users U INNER JOIN contacts C on U.id=c.uid;

1. Analyze database data with Databasemetadate

Public void dbm () throws exception{

Connection con = datasourceutils. Getconn ();

DatabaseMetaData dm= con.getmetadata ();

ResultSet rs= Dm.getcatalogs ();//Get all database names

while (Rs.next ()) {

String name = rs.getstring ("Table_cat");

SYSTEM.ERR.PRINTLN (name);

//     }

System.err.println ("======================");

String dbName = Dm.getdatabaseproductname ();//Database name

System. err. println (DbName);

System. err. println ("How many tables are in the database:");

ResultSet rs2 = dm.gettables ("db909", "db909",null,new string[]{"TABLE"});

while (Rs2.next ()) {

String tableName = rs2.getstring ("table_name");

System. err. println (TableName);

}

}

2. Analyze the result set with Resultsetmetadate

This class is used to parse the result set of a query:

How many columns, column names, and types of columns are analyzed?

@Test

Public void rs2 () throws exception{

Connection con = datasourceutils. Getconn ();

Go to the exam database.

Statement st = Con.createstatement ();

St.execute ("Use exam");

Inquire

String sql = "SELECT * FROM dept";

ResultSet rs = st.executequery (SQL);

Analysis of RS result set

ResultSetMetaData Rsmd=rs.getmetadata ();

Gets a few columns

int cols = Rsmd.getcolumncount ();

System. err. println (cols);

Get the name of each field

list<string> colnames = new arraylist<string> ();//Save all fields

for (int i=0;i<cols;i++) {

String colname = Rsmd.getcolumnname (i+1);

System. err. Print (colname+ "\t\t");

colNames.Add (colname);

}

System. err. println ();

Get Data

while (Rs.next ()) {

for (String nm:colnames) {//Iterate through the columns in a row

String val = rs.getstring (nm);

System. err. Print (val+ "\t\t");

}

System. err. println ();

}

Con.close ();

}

Java Learning Note-c3p0 connection pooling and meta data Analysis (42)