本文主要是介绍连接池的作用就是为了提高性能，既然能提高性能还等啥，我们自己模拟编写一个连接池，探其究竟，明其原理。，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
连接池的作用就是为了提高性能。
连接池的作用：连接池是将已经创建好的连接保存在池中，当有请求来时，直接使用已经创建好的连接对数据库进行访问。这样省略了创建连接和销毁连接的过程。这样性能上得到了提高。
基本原理是这样的：
- 建立数据库连接池对象（服务器启动）。
- 按照事先指定的参数创建初始数量的数据库连接（即：空闲连接数）。
- 对于一个数据库访问请求，直接从连接池中得到一个连接。如果数据库连接池对象中没有空闲的连接，且连接数没有达到最大（即：最大活跃连接数），创建一个新的数据库连接。
- 存取数据库。
- 关闭数据库，释放所有数据库连接（此时的关闭数据库连接，并非真正关闭，而是将其放入空闲队列中。如实际空闲连接数大于初始空闲连接数则释放连接）。
- 释放数据库连接池对象（服务器停止、维护期间，释放数据库连接池对象，并释放所有连接）。
连接池的概念和为什么要使用连接池？
连接池放了N个Connection对象，本质上放在内存当中，在内存中划出一块缓存对象，应用程序每次从池里获得Connection对象，而不是直接从数据里获得，这样不占用服务器的内存资源。
如果不使用连接池会出现的情况：
- 占用服务器的内存资源
- 导致服务器的速度非常慢
既然，大家都了解了连接池的好处，那么我就动手写个固定大小的连接池，以方便伙伴们学习和交流。话不多说，直接上代码，走着~
package com.smallfan.connectionpool;import com.smallfan.TestVisiblity;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;import java.sql.*;
import java.util.Map;
import java.util.Properties;
import java.util.concurrent.Executor;
import java.util.concurrent.atomic.AtomicIntegerArray;/*** @PACKAGE_NAME: com.smallfan.connectionpool* @NAME: ConnectionPool* @USER: dell* @DATE: 2020/5/28* @PROJECT_NAME: aboutthread* 模拟实现固定大小的数据库连接池*/
public class TestPool{public static void main(String[] args) {//初始化连接池ConnectionPool pool = new ConnectionPool(2);for (int i = 0; i < 5; i++) {//创建5个线程争抢连接池new Thread(()->{Connection apply = pool.apply();try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}pool.free(apply);}).start();}}
}
class ConnectionPool {static Logger logger = LoggerFactory.getLogger(ConnectionPool.class);//初始化连接池池大小private final int poolSize;//使用数组存储连接对象private Connection[] connections;//使用原子数组记录连接池状态 0：空闲 1：繁忙private AtomicIntegerArray status;//初始化public ConnectionPool(int poolSize) {this.poolSize = poolSize;this.connections = new Connection[poolSize];this.status = new AtomicIntegerArray(new int[poolSize]);for (int i = 0; i < poolSize; i++) {//初始化数据库连接connections[i] = new TestConnection("连接"+i);}}//申请连接public Connection apply(){while (true){for (int i = 0; i < poolSize; i++) {if(status.get(i) == 0){//是否存在空闲的连接if(status.compareAndSet(i,0,1)){//更新空闲连接为繁忙状态，保证原子操作并返回truelogger.info("获取连接 {}",connections[i]);return connections[i];}}}//若都是繁忙状态，阻塞synchronized (this){try {logger.info("等待连接");this.wait();} catch (InterruptedException e) {e.printStackTrace();}}}}//释放连接public void free(Connection connection){for (int i = 0; i < poolSize; i++) {if (connections[i] == connection){logger.info("释放连接{}",connections[i]);status.set(i,0);synchronized (this){this.notifyAll();}break;}}}}
//模拟实现Connection接口
class TestConnection implements Connection{String name;public TestConnection(String name) {this.name = name;}@Overridepublic String toString() {return "TestConnection{" +"name='" + name + '\'' +'}';}public Statement createStatement() throws SQLException {return null;}public PreparedStatement prepareStatement(String sql) throws SQLException {return null;}public CallableStatement prepareCall(String sql) throws SQLException {return null;}public String nativeSQL(String sql) throws SQLException {return null;}public void setAutoCommit(boolean autoCommit) throws SQLException {}public boolean getAutoCommit() throws SQLException {return false;}public void commit() throws SQLException {}public void rollback() throws SQLException {}public void close() throws SQLException {}public boolean isClosed() throws SQLException {return false;}public DatabaseMetaData getMetaData() throws SQLException {return null;}public void setReadOnly(boolean readOnly) throws SQLException {}public boolean isReadOnly() throws SQLException {return false;}public void setCatalog(String catalog) throws SQLException {}public String getCatalog() throws SQLException {return null;}public void setTransactionIsolation(int level) throws SQLException {}public int getTransactionIsolation() throws SQLException {return 0;}public SQLWarning getWarnings() throws SQLException {return null;}public void clearWarnings() throws SQLException {}public Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException {return null;}public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {return null;}public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {return null;}public Map<String, Class<?>> getTypeMap() throws SQLException {return null;}public void setTypeMap(Map<String, Class<?>> map) throws SQLException {}public void setHoldability(int holdability) throws SQLException {}public int getHoldability() throws SQLException {return 0;}public Savepoint setSavepoint() throws SQLException {return null;}public Savepoint setSavepoint(String name) throws SQLException {return null;}public void rollback(Savepoint savepoint) throws SQLException {}public void releaseSavepoint(Savepoint savepoint) throws SQLException {}public Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {return null;}public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {return null;}public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {return null;}public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException {return null;}public PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException {return null;}public PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException {return null;}public Clob createClob() throws SQLException {return null;}public Blob createBlob() throws SQLException {return null;}public NClob createNClob() throws SQLException {return null;}public SQLXML createSQLXML() throws SQLException {return null;}public boolean isValid(int timeout) throws SQLException {return false;}public void setClientInfo(String name, String value) throws SQLClientInfoException {}public void setClientInfo(Properties properties) throws SQLClientInfoException {}public String getClientInfo(String name) throws SQLException {return null;}public Properties getClientInfo() throws SQLException {return null;}public Array createArrayOf(String typeName, Object[] elements) throws SQLException {return null;}public Struct createStruct(String typeName, Object[] attributes) throws SQLException {return null;}public void setSchema(String schema) throws SQLException {}public String getSchema() throws SQLException {return null;}public void abort(Executor executor) throws SQLException {}public void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException {}public int getNetworkTimeout() throws SQLException {return 0;}public <T> T unwrap(Class<T> iface) throws SQLException {return null;}public boolean isWrapperFor(Class<?> iface) throws SQLException {return false;}
}查看输出结果：
2020-05-28 23:37:18:687 [Thread-2] 等待连接
2020-05-28 23:37:18:689 [Thread-0] 获取连接 TestConnection{name='连接1'}
2020-05-28 23:37:18:689 [Thread-1] 获取连接 TestConnection{name='连接0'}
2020-05-28 23:37:18:716 [Thread-4] 等待连接
2020-05-28 23:37:18:716 [Thread-3] 等待连接
2020-05-28 23:37:19:717 [Thread-1] 释放连接TestConnection{name='连接0'}
2020-05-28 23:37:19:717 [Thread-0] 释放连接TestConnection{name='连接1'}
2020-05-28 23:37:19:718 [Thread-3] 获取连接 TestConnection{name='连接0'}
2020-05-28 23:37:19:718 [Thread-2] 等待连接
2020-05-28 23:37:19:718 [Thread-4] 获取连接 TestConnection{name='连接1'}
2020-05-28 23:37:20:732 [Thread-3] 释放连接TestConnection{name='连接0'}
2020-05-28 23:37:20:732 [Thread-2] 获取连接 TestConnection{name='连接0'}
2020-05-28 23:37:20:732 [Thread-4] 释放连接TestConnection{name='连接1'}
2020-05-28 23:37:21:732 [Thread-2] 释放连接TestConnection{name='连接0'}好像没有什么问题，欢迎伙伴们交流讨论，等你哦~
这篇关于连接池的作用就是为了提高性能，既然能提高性能还等啥，我们自己模拟编写一个连接池，探其究竟，明其原理。的文章就介绍到这儿，希望我们推荐的文章对编程师们有所帮助！
