Quick start to connection pooling

• Catalog

  Background of database connection

  Database connection pool

  DataSource

  Custom database connection pool

  demonstration

  test

  ---

• Background of database connection

• Database connection is a key 、 Limited 、 Expensive resources
• This is especially prominent in multi-user web applications
• The management of database connections can significantly affect the performance of the entire application Performance indicators , Database connection pool is proposed to solve this problem
• Such as ： When users visit the website, they constantly create connections and constantly destroy connections , Then the efficiency is not very high

• Database connection pool

• Database connection pool To be responsible for the distribution of , Manage and release database connections
• It allows applications to Reuse An existing database connection , Instead of building a new
• This technology can obviously improve the performance of database operation
• Brief process ：
• Is to prepare a container in advance , This container is the connection pool of the database , In the container , Prepare some database connections in advance
• Then came the request , Take a connection object from the connection pool and use it
• Don't turn it off after use , Instead, it is returned to the connection pool , Achieve the effect of reuse
• The so-called pool , Is to make a container , Many database connection objects are stored in this container

• DataSource

• DataSource Interface Overview
• javax.sql.DataSourse Interface : data source ( Database connection pool )
• Java Official database connection pool specification ( Interface )
• If you want to complete the database connection pool technology , It has to happen DataSource Interface
• Core functions ：
• Get database connection object ：
• Connection getConnection();

• Custom database connection pool

• 1. Define a class , Realization DataSource Interface
• 2. Define a container , Used to save multiple Connection Connection object
• 3. Define static code blocks , adopt JDBC Utility class acquisition 10 Save the connection to the container
• 4. rewrite getConnection Method , Get a connection from the container and return
• 5. Definition getSize Method , Used to get the size of the container and return

• demonstration

• 

• package demo02.myDataSourse;
  import demo02.utils.JDBCUtils;
  
  import javax.sql.DataSource;
  import java.io.PrintWriter;
  import java.sql.Connection;
  import java.sql.SQLException;
  import java.sql.SQLFeatureNotSupportedException;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  import java.util.logging.Logger;
  
  // Custom database connection pool 
  public class demoDataSourse implements DataSource{
      //1. Preparation container , Used to save multiple connection objects 
      private static List<Connection> pool = Collections.synchronizedList(new ArrayList<>());
      //2. Define static code blocks , Get... Through the tool class 10 A connection object 
      static{
          for(int i=1;i<=10;i++){
              Connection con = JDBCUtils.getConnection();
              pool.add(con);
          }
      }
      //3. rewrite getConnection(), Used to get a connection object 
      @Override
      public Connection getConnection() throws SQLException {
          if(pool.size()>0){
              Connection con = pool.remove(0);
              return con;
          }else{
              throw new RuntimeException(" The number of connections has been exhausted ");
          }
      }
      //4. Definition getSize Method , Gets the size of the connection pool container 
      public int getSize(){
          return pool.size();
      }
      @Override
      public Connection getConnection(String username, String password) throws SQLException {
          return null;
      }
  
      @Override
      public <T> T unwrap(Class<T> iface) throws SQLException {
          return null;
      }
  
      @Override
      public boolean isWrapperFor(Class<?> iface) throws SQLException {
          return false;
      }
  
      @Override
      public PrintWriter getLogWriter() throws SQLException {
          return null;
      }
  
      @Override
      public void setLogWriter(PrintWriter out) throws SQLException {
  
      }
  
      @Override
      public void setLoginTimeout(int seconds) throws SQLException {
  
      }
  
      @Override
      public int getLoginTimeout() throws SQLException {
          return 0;
      }
  
      @Override
      public Logger getParentLogger() throws SQLFeatureNotSupportedException {
          return null;
      }
  }

• test

• The test here does not return the connected object , It's a direct shut down
• There are effects in the presentation , How to return it will be introduced later
• 
• 

• package demo02.myDataSourse;
  
  import java.sql.Connection;
  import java.sql.PreparedStatement;
  import java.sql.ResultSet;
  
  public class demoDataSourseTest {
      public static void main(String[] args) throws Exception {
          //1. Create connection pool object 
          demoDataSourse dataSourse = new demoDataSourse();
  
          System.out.println(" Quantity before use " + dataSourse.getSize());
  
          //2. Get the connection object through the connection pool object 
          Connection con = dataSourse.getConnection();
          //3. Query all the information in the student table 
          String sql = "SELECT * FROM student";
          PreparedStatement pst = con.prepareStatement(sql);
          //4. perform sql sentence , Receive the result set 
          ResultSet rs = pst.executeQuery();
          //5. Processing result set 
          while(rs.next()){
              System.out.println(rs.getInt("sid")+"\t"+rs.getString("name")+"\t"+rs.getInt("age")+"\t"+rs.getDate("birthday"));
          }
          //6. Release resources 
          rs.close();
          pst.close();
          con.close();// After use , Not returned to close the connection ; Return later 
  
          System.out.println(" Quantity after use " + dataSourse.getSize());
      }
  }