Java learning notes-c3p0 connection pool and metadata analysis (42), learning notes c3p0

Java learning notes-c3p0 connection pool and metadata analysis (42), learning notes c3p0
Step 1: import the c3p0 package

Step 2: Create a c3p0-config.xml under the classpath directory

<? Xml version ="1.0"Encoding =UTF-8"?>

<C3p0-config>

<! -- Default configuration, which can only appear once -->

<Default-config>

<! -- Set connection timeout to 30 seconds -->

<Property name ="CheckoutTimeout"& Gt; 30000 </property>

<! -- Check the idle connection once in 30 seconds -->

<Property name ="IdleConnectionTestPeriod"> 30 </property>

<! -- Size of the initialized pool -->

<Property name ="InitialPoolSize"> 2 </property>

<! -- The maximum idle time of a connection -->

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

<! -- Maximum number of connections allowed -->

<Property name ="MaxPoolSize"> 10 </property>

<! -- The minimum pool has several connections -->

<Property name ="MinPoolSize"> 2 </property>

<! -- Batch statement

-->

<Property name ="MaxStatements"> 50 </property>

<! -- Increase several connections each time -->

<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"& Gt; 1234 </property>

</Default-config>

C3p0-config>

Step 3: Create a factory class to obtain the connection

PackageCn. itcast. utils;

ImportJava. SQL. Connection;

ImportJavax. SQL. DataSource;

ImportCom. mchange. v2.c3p0. ComboPooledDataSource;

Public ClassDataSourceUtils {

Private StaticDataSourceDs;

Static{

Ds= // Default read c3p0-config.xml Default Configuration

NewComboPooledDataSource ();

}

Public StaticDataSource getDatasSource (){

Return Ds;

}

Public StaticConnection getConn (){

Connection con =Null;

Try{

Con =Ds. GetConnection (); // each time a new connection is obtained from ds

}Catch(Exception e ){

E. printStackTrace ();

}

ReturnCon;

}

}

ComboPooledDataSource has three structures:

No parameter.

Receives a boolean

By default, true indicates that all connection. autoCommit attributes are true.

Receives a string

In a c3p0-config.xml file, you can configure multiple connections. All connections except the default connections are named connections. Pass

<Named-config name = "xxxx"/>

 

Specify a named connection:

<! -- Default configuration, which can only appear once -->

<Named-config name ="Db909">

<Property name ="CheckoutTimeout"& Gt; 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"& Gt; 1234 </property>

</Named-config>

 

Connect to the database by name in the Code:

Ds=

NewComboPooledDataSource ("db909 ");

Summary:

C3p0 Connection pool. Connection is encapsulated only when the user obtains the Connection.

Metadata Analysis

Metadata is used to analyze all the information of a database when only one object is connected.

DataBaseMetadate-indicates the database information.

ResultSetMetadate-specifies the type of the data result. Core.

To perform metadata analysis, you must use statement and 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],]

 

Export all tables and data in a specified database to excel.

 

Create view uc

SELECT u. name AS uname, c. name AS cname

FROM users u inner join contacts c ON u. id = c. uid;

1. Use databasemetadate to analyze database data

Public VoidDbm ()ThrowsException {

Connection con = performanceutils.GetConn();

DatabaseMetaData dm = con. getMetaData ();

// ResultSet rs = dm. getCatalogs (); // obtain 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,NewString [] {"TABLE "});

While(Rs2.next ()){

String tableName = rs2.getString ("TABLE_NAME ");

System.Err. Println (tableName );

}

}

2. Use ResultSetMetadate to analyze the result set

This class is used to analyze the query result set:

There are several columns in the analysis. What are the column types?

@ Test

Public VoidRs2 ()ThrowsException {

Connection con = performanceutils.GetConn();

// Go to exam Database

Statement st = con. createStatement ();

St.exe cute ("use exam ");

// Query

String SQL = "select * from dept ";

ResultSet rs = st.exe cuteQuery (SQL );

// Analyze the rs result set

ResultSetMetaData rsmd = rs. getMetaData ();

// Obtain several columns

IntCols = rsmd. getColumnCount ();

System.Err. Println (cols );

// Obtain the name of each field

List <String> colNames =NewArrayList <String> (); // save all fields

For(IntI = 0; I <cols; I ++ ){

String colName = rsmd. getColumnName (I + 1 );

System.Err. Print (colName + "\ t ");

ColNames. add (colName );

}

System.Err. Println ();

// Obtain data

While(Rs. next ()){

For(String nm: colNames) {// traverse the columns in a row

String val = rs. getString (nm );

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

}

System.Err. Println ();

}

Con. close ();

}