1Metadata _

1.1 Function _

Using metadata, you can write the parameters of the jdbc precompiled statement and the number and name of the results of the ResultSet .

1.2 Three kinds of metadata

1 ) Database meta object ( DatabaseMetaData )

To know which database to connect to, you must use the metadata object of the database

2 ) Parameter meta object ( ParameterMetaData )

insert into studnetx(xxxx) values(?,?);

After precompiling sql , knowing that the precompiled sql has several parameters, you must use parameter metadata

3 ) The result set meta object (ResultSetMetaData)

ResultSet rs

Know the number of fields in the table, and field names, you must use the metadata of the result set

1.3 Methods

ParameterMetaData pmd = stmt.getParameterMetaData();// Get parameter metadata

int paramCount = pmd.getParameterCount();// Get the number of placeholder parameters

ResultSetMetaData rsmd = rs.getMetaData();// Get the result set metadata of the returned result

int columnCount = rsmd.getColumnCount(); //Get the number of columns

String columnName = rsmd.getColumnName(i); //to the field name

2 DBUtils Tools

2.1 Introduction _

Simple jdbc code encapsulation

2.2 Guide package

commons-dbutils-1.2.jar

2.3 APIs used

QueryRunner class : Through this class, you can perform update operations or query operations.

update(.....): for update operations ( DDL , DML )

query(.....): for query operations ( DQL )

ResultSetHandler interface : used to encapsulate the results after the query.

Object handle(ResultSet rs) : used to encapsulate data

2.4 Methods

QueryRunner qr = new QueryRunner(conn)；

qr.update("sql", new Object[]{ parameter list }); // Update query

qr.query("ssql", implementation class of ResultSetHandler interface, new Object[]{parameter list});

Common implementation classes of ResultSetHandler():

ArrayHandler : Encapsulates the data of the first row of the result set into an array of objects.

ArrayListHandler : Encapsulates each row of data in the result set into an array of objects, and puts this array of objects into a List

BeanHandler : encapsulates the first line of data in the result set into a javabean object

BeanListHandler : encapsulates each row of data in the result set into a javabean object , and puts this javabean into the List

Map Handler : Encapsulate the first row of data in the result set into a map object

ScalarHandler : Get the first row and first column of the result set. Typically used for aggregate function queries. For example ( count()/max() )

Note: If the field name of the table is inconsistent with the property name of the javabean , you need to customize the implementation class of ResultSetHandler

3 connection pool

3.1 Introduction _

Store commonly used connection objects ( N for each connection , convenient for different users to connect )

3.2 Common connection pooling tools

Note: The DataSource interface is an interface designed by Sun to standardize the implementation of connection pools.

Connection Pool Tool 1 : DBCP (Datatabse Connection Pool)

Is a product of the Apache organization. Default implementation of connection pool for Tomcat server

Steps for usage:

1 ) Guide package

commons-dbcp-1.4.jar core package

commons-pool-1.5.6.jar auxiliary package

2 ) Create a connection pool object BasicDataSource object

3 ) Set connection parameters ( url , user , password , dirverClass )

4 ) Set connection pool parameters (initial number of connections, maximum number of connections, maximum waiting time)

5 ) Get the connection object ( getConnection() method)

//1) Create a dbcp connection pool object

BasicDataSource bds = new BasicDataSource();

BasicDataSource bds = (BasicDataSource)BasicDataSourceFactory.createDataSource(properties配置文件);

// The Key of the configuration file should be consistent with the following setxxx .

//2) Set the connection parameters

bds.setUrl(url);

bds.setUsername(user);

bds.setPassword(password);

bds.setDriverClassName(driverClass);

//3) Set the connection pool parameters

bds.setInitialSize(5);//Initialize the connection

bds.setMaxActive(10);//Maximum number of connections

bds.setMaxWait(3000);//When the maximum number of connections is exceeded, the maximum waiting time is 3 seconds

Connection conn = bds.getConnection(); //Get the connection from the connection pool

conn.close();// Put the connection object back into the connection pool.

Connection Pool Tool 2 : C3P0

Is an open source framework ( hibernate built-in default connection pool tool C3P0) )

Steps for usage:

1 ) Import the jar package of c3p0

c3p0-0.9.1.2.jar core package

2 ) Create a connection pool object ComboPooledDataSource object

3 ) Set connection parameters ( url , user , password , dirverClass )

4 ) Set connection pool parameters (initial number of connections, maximum number of connections, maximum waiting time)

5 ) Get the connection object ( getConnection() method)

//1) Create a connection pool object

ComboPooledDataSource cds = new ComboPooledDataSource();

/**

* The method of using xml configuration file to read c3p0

* Notice:

* 1) A file named c3p0-config.xml needs to be placed in the src directory, and c3p0 will automatically read this file.

* 2) The attribute name in the xml configuration file is consistent with the manual setting method name! ! ! ! c3p0 will automatically read

/**

* //1) Create a connection pool object

* 1)new ComboPooledDataSource(): Use the construction method without parameters and read the configuration information of default-config

* 2) new ComboPooledDataSource (the attribute value of name): Use the parameterized construction method to read the name-config configuration information

//2) Set the connection parameters

cds.setJdbcUrl(url);

cds.setUser(user);

cds.setPassword(password);

cds.setDriverClass(driverClass);

//3) Set the parameters related to the connection pool

cds.setInitialPoolSize(5);//Initialize the number of connections

cds.setMaxPoolSize(10);//Maximum number of connections

cds.setCheckoutTimeout(3000);//Maximum waiting time

cds.setMinPoolSize(3); //Minimum number of connections

//4) Get the connection

Connection conn = cds.getConnection();

//5)把连接对象放回连接池中

conn.close();

<c3p0-config>

<default-config>

<property name="jdbcUrl">jdbc:mysql://localhost:3306/day18</property>

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

</default-config>

<named-config name="oracle">