JDBC database connection pool

JDBC Database connection pool

1. Concept

• It's actually a container （ aggregate ）, Container for database connection .

  • When the system is initialized , The container is created , Some database connection objects will be applied in the container , When the user comes to access the database , Get the connection object from the container , The user returns the connection to the container after accessing the database .

2. benefits

• Saving resource
• Efficient user access

2. Realization

• 

2.1 Standard interface

• Standard interface :DataSourcejava.sql Under bag
• Method
  • Get the connection ：getConnection()
  • Return connection ：Connection.close(). If Connection It's taken from the connection pool , that close() Method , Will not close the connection . But return the connection

2.2 C3P0 Database connection pool

1. rely on jar package

• Address connection :Mchange Commons Java,C3P0

2. Define configuration file

• name ：c3p0.properties perhaps c3p0-config.xml

  <?xml version="1.0" encoding="UTF-8"?>
  
  <c3p0-config>
      <default-config>
          <!--  Connection parameter settings , Password and driver  -->
          <property name="driverClass">com.mysql.jdbc.Driver</property>
          <property name="jdbcUrl">jdbc:mysql://127.0.0.1:3306/test?serverTimezone=UTC</property>
          <property name="user">root</property>
          <property name="password">root</property>
  
          <!--  Connection pool parameters  -->
          <!--  Initial number of applications  -->
          <property name="initialPoolSize">10</property>
  
  <!-- <property name="maxIdleTime">30</property>-->
          <!--  maximum connection  -->
          <property name="maxPoolSize">100</property>
  <!-- <property name="minPoolSize">10</property>-->
          <!-- Set timeout -->
          <property name="checkoutTimeout">3000</property>
      </default-config>
  
      <named-config name="mySource">
          <property name="driverClass">com.mysql.jdbc.Driver</property>
          <property name="jdbcUrl">jdbc:mysql://localhost:3306/bookstore</property>
          <property name="user">root</property>
          <property name="password">xxxx</property>
  
          <property name="initialPoolSize">10</property>
          <property name="maxIdleTime">30</property>
          <property name="maxPoolSize">100</property>
          <property name="minPoolSize">10</property>
      </named-config>
  </c3p0-config>
  

• route ： Directly on src Under the table of contents .

3. Create the core object and get the connection object

• Create objects ComboPooledDataSource()
• Get objects ds.getConnection()

package com.sql.one;

import com.mchange.v2.c3p0.ComboPooledDataSource;

import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.SQLException;

public class C3P0Demo {
    
    public static void main(String[] args) throws SQLException {
    
        // Create database connection pool object 
        DataSource ds=new ComboPooledDataSource();
        // Get the connection object 
        Connection conn=ds.getConnection();
        //3. Print connection 
        System.out.println(conn);
    }
}

package com.sql.one;

import com.mchange.v2.c3p0.ComboPooledDataSource;

import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.SQLException;

public class C3P0Demo {
    
    public static void main(String[] args) throws SQLException {
    
        // Create database connection pool object , Parameters can be passed in xml In the configuration file name Use other cheap 
        DataSource ds=new ComboPooledDataSource();
        // Get the connection object 
// Connection conn=ds.getConnection();
        //3. Print connection 
        for(int i=1;i<=10;i++){
    
            Connection conns=ds.getConnection();
            System.out.println(i+":"+conns);
            if(i==5){
    
                conns.close();// Returning the connection is not closing 
            }
        }
    }
}

2.3 Druid Database connection pool

1. rely on jar package

Address ：https://mvnrepository.com/artifact/com.alibaba/druid

2. Define configuration file

#  Drive loading 
driverClassName=com.mysql.jdbc.Driver
#  Registration drive 
url=jdbc:mysql://127.0.0.1:3306/test?serverTimezone=UTC
# user
username=root
# password
password=password123
#  The number of physical connections established in the pool during initialization .
initialSize=2
#  Maximum number of active connection pools 
maxActive=50
#  The maximum waiting time unit is milliseconds ,60*1000 =1 minute 
maxWait=60000

• You can call it anything , It can be placed in any directory

3. Get database connection pool

• adopt Factory To get DruidDataSourceFactory

• package com.sql.one;
  
  import com.alibaba.druid.pool.DruidDataSourceFactory;
  
  import javax.sql.DataSource;
  import java.io.InputStream;
  import java.util.Properties;
  import java.sql.Connection;
  
  public class DruidDemo {
        
      public static void main(String[] args)throws Exception{
        
          //1. Import jar package 
          //2. Load profile 
          Properties pro =new Properties();
          InputStream is =DruidDemo.class.getClassLoader().getResourceAsStream("druid.properties");
          pro.load(is);
          //4. Get connection pool object , Using factory mode 
          DataSource ds= DruidDataSourceFactory.createDataSource(pro);
          //5. Get the connection 
          Connection conn= ds.getConnection();
          System.out.println(conn);
  
      }
  }
  
  

4. Get the connection

3. Encapsulation of tool class

3.1 summary

• Define a class JDBCUtils

• Provide static code block loading configuration file , Initialize connection pool object

• Provide methods

  • Get the connection method ： Get the connection through the database connection pool
  • Release resources
  • How to get the connection pool

3.2 Test use

package com.sql.one;

import com.sql.jdbcutils.JDBCUtils;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;

public class DuridDemo2 {
    public static void main(String[] args) {
        try {
            Connection conn= JDBCUtils.getConnection();
            String sql="insert into t1 values(null,?,?)";
            PreparedStatement pstmt= conn.prepareStatement(sql);
            // to SQL Medium ？ assignment 
            pstmt.setString(1," Logic ");
            pstmt.setInt(2,30);
            int count=pstmt.executeUpdate();
            System.out.println(count);
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
    }
}

4.Spring JDBC

4.1 summary

call JdbcTemplate To complete CRUD operation

• update(): perform DML sentence . increase 、 Delete 、 Change statement .

• queryForMap(): Query results , Encapsulate the result set as map aggregate

• queryForList(): The query results are encapsulated as list aggregate

• query(): The query result is returned as JavaBean object

• queryForObject: Query results , Encapsulate the results as objects .

4.2 Easy to use

• The import related jar package

  

• Easy to use , But the premise is to have a database connection pool DataSource

• package com.sql.jdbctemplate;
  
  import com.sql.jdbcutils.JDBCUtils;
  import org.springframework.jdbc.core.JdbcTemplate;
  
  public class JDBCTemplate {
        
      public static void main(String[] args) {
        
          //1. Import jar package 
          //2. establish JDBCTemplate object 
  
          JdbcTemplate template =new JdbcTemplate(JDBCUtils.getDataSource());
          //3. Calling method 
          String sqlstr="insert into t1 values(null,?,?)";
          int count = template.update(sqlstr, " Shi Qiang ", 30);
          System.out.println(" Insert "+count+" Data succeeded ");
      }
  }
  
  

  

4.3 Simple use of test module

• Annotate the function name @Test, Then the modified function can be executed independently , Independent of the main method .

  

4.4 Introduction of common methods

1. update() Method

• Returns the number of entries inserted into the database .

package com.sql.jdbctemplate;

import com.sql.jdbcutils.JDBCUtils;
import org.testng.annotations.Test;
import org.springframework.jdbc.core.JdbcTemplate;

public class JdbcTemplateDemo2 {
    
    // Instantiation JdbcTemplate
    JdbcTemplate template= new JdbcTemplate(JDBCUtils.getDataSource());
    //Junit  unit testing , The method can be executed independently , Use @Test annotation ,
    @Test
    public void test1(){
    
        String sqlstr="insert into t1 values(null,?,?)";
        int count = template.update(sqlstr, " AI AA", 30);
        System.out.println(" Insert "+count+" Data succeeded ");
        //System.out.println(" I was executed ");
    }
}

2. queryForMap () Method

• return map aggregate , There can only be one result .

• 	@Test
      public void test2(){
          String sqlstr="select * from t1 where id=1";
          Map<String, Object> map = template.queryForMap(sqlstr);
          System.out.println(map);
      }
  
  	//{id=1, username= The east , age=21}
  

• 

• Two returned results will report an error . because map The key of is unique .

  

• An error will also be reported if there is no returned result .

  

3. queryForList () Method

• The query results are encapsulated as list aggregate , Each record will be encapsulated in map aggregate , In the package in list in .

• 	@Test
      public void test3(){
        
          String sqlstr="select * from t1";
          List<Map<String, Object>> maps = template.queryForList(sqlstr);
  
          for (Map<String, Object> map : maps) {
        
              System.out.println(map);
          }
      }
  

  

4. query() Method

• This method is most commonly used .

  • new BeanPropertyRowMapper< class >( class .class)
    

• return JavaBean Encapsulated objects .

• First, create the corresponding class

  package com.sql.jdbctemplate;
  
  public class Role {
        
      private Integer id;
      private String username;
      private Integer age;// Use the referenced data type to prevent null values in the database (null) Data of 
  
      public Role(Integer id, String username, Integer age) {
        
          this.id = id;
          this.username = username;
          this.age = age;
      }
  
      public Role() {
        
      }
  
      public Integer getId() {
        
          return id;
      }
  
      public void setId(Integer id) {
        
          this.id = id;
      }
  
      public String getUsername() {
        
          return username;
      }
  
      public void setUsername(String username) {
        
          this.username = username;
      }
  
      public Integer getAge() {
        
          return age;
      }
  
      public void setAge(Integer age) {
        
          this.age = age;
      }
  
      @Override
      public String toString() {
        
          return "Role{" +
                  "id=" + id +
                  ", username='" + username + '\'' +
                  ", age=" + age +
                  '}';
      }
  }
  
  

• The first method （ More complicated , Not recommended ）.

  

• The second method

      @Test
      public void test4(){
        
          String sqlstr="select * from t1";
          // Using generics and reflection will correspond to JavaBean Load into memory for use 
          List<Role> list= template.query(sqlstr,new BeanPropertyRowMapper<Role>(Role.class));
          for(Role r : list){
        
              System.out.println(r);
          }
      }
  

  

• ** notes ：** If fields and bean Fields in do not match , Can be in SQL Alias in statement .

5. queryForObject() Method

• Generally used to execute Aggregate functions Of sql sentence , for example count,sum,avg

•     @Test
      public void test5(){
        
          String sqlstr="select count(1) from t1";
          // except SQL Statement also passes in the type of the return value , The return value is received with the specified type 
          Long count=template.queryForObject(sqlstr,Long.class);
          System.out.println(count);
      }
  

  

5. Supplement of shortcut keys

• Return value ：idea in ctrl+Alt+V Quickly generate return values .
• for loop ：iter enhance for loop ,fori Ordinary for loop .

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