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一、引言
池化技术在java中应用的很广泛，简而论之，使用对象池存储某个实例数受限制的实例，开发者从对象池中获取实例，使用完之后再换回对象池，从而在一定程度上减少了系统频繁创建对象销毁对象的开销。java线程池和数据库连接池就是典型的应用，但并非所有的对象都适合拿来池化，对于创建开销比较小的对象拿来池化反而会影响性能，因为维护对象池也需要一定的资源开销，对于创建开销较大，又频繁创建使用的对象，采用池化技术会极大提高性能。
业界有很多成熟的数据库连接池，比如c3p0，dbcp，proxool以及阿里的druid。很多以及开源，在github可以找到源码，开发者可以根据自己的需求结合各种连接池的特点和性能进行选择。本文仅是为了了解学习池化技术，实现的一个简单的数据库连接池，如有错误，还望批评指正。
二、设计
主要类和接口
.connectionparam - 数据库连接池参数类，负责配置数据库连接以及连接池相关参数。使用builder实现。
driver url user password - 连接数据库所需
minconnection - 最小连接数
maxconnection - 最大连接数
minidle - 最小空闲连接数
maxwait - 最长等待时间
private final string driver; private final string url; private final string user; private final string password; private final int minconnection; private final int maxconnection; private final int minidle; private final long maxwait;
.connectionpool - 数据库连接池
connectionpool构造方法声明为保护，禁止外部创建，交由connectionpoolfactory统一管理。
connectionpool实现datasource接口，重新getconnection()方法。
connectionpool持有两个容器 - 一个queue存储空闲的connection，另一个vector（考虑到同步）存储正在使用的connection。
当开发者使用数据库连接时，从queue中获取，没有则返回空；使用完成close连接时，则放回vector。
connectionpool提供了一个简单的基于minidle和maxconnection的动态扩容机制。
private static final int initial_size = 5; private static final string close_method = "close"; private static logger logger; private int size; private connectionparam connectionparam; private arrayblockingqueue<connection> idleconnectionqueue; private vector<connection> busyconnectionvector;
.connectionpoolfactory - 连接池管理类
connectionpoolfactory持有一个静态concurrenthashmap用来存储连接池对象。
connectionpoolfactory允许创建多个不同配置不同数据库的连接池。
开发者首次需要使用特定的名称注册（绑定）连接池，以后每次从指定的连接池获取connection。
如果连接池不再使用，开发者可以注销（解绑）连接池。
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private static map<string, connectionpool> poolmap = new concurrenthashmap<>();
public static connection getconnection(string poolname) throws sqlexception {
namecheck(poolname);
connectionpool connectionpool = poolmap.get(poolname);
return connectionpool.getconnection();
}
public static void registerconnectionpool(string name, connectionparam connectionparam) {
registercheck(name);
poolmap.put(name, new connectionpool(connectionparam));
}
// let gc
public static void unregisterconnectionpool(string name) {
namecheck(name);
final connectionpool connectionpool = poolmap.get(name);
poolmap.remove(name);
new thread(new runnable() {
@override
public void run() {
connectionpool.clear();
}
}).start();
}
核心代码
数据库连接池核心代码在于getconnection()方法，通常，开发者处理完数据库操作后，都会调用close()方法，connection此时应该被关闭并释放资源。而在数据库连接池中，用户调用close()方法，不应直接关闭connection，而是要放回池中，重复使用，这里就用到java动态代理机制，getconnection返回的并不是“真正”的connection，而是自定义的代理类(此处使用匿名类)，当用户调用close()方法时，进行拦截，放回池中。有关动态代理，可以参看另一篇博客《java动态代理简单应用》
@override
public connection getconnection() throws sqlexception {
try {
final connection connection = idleconnectionqueue.poll(connectionparam.getmaxwait(), timeunit.milliseconds);
if (connection == null) {
logger.info(emptymsg());
ensurecapacity();
return null;
}
busyconnectionvector.add(connection);
return (connection) proxy.newproxyinstance(this.getclass().getclassloader(),
new class[]{connection.class}, new invocationhandler() {
@override
public object invoke(object proxy, method method, object[] args) throws throwable {
if (!method.getname().equals(close_method)) {
return method.invoke(connection, args);
} else {
idleconnectionqueue.offer(connection);
busyconnectionvector.remove(connection);
return null;
}
}
});
} catch (interruptedexception e) {
e.printstacktrace();
}
return null;
}
二、使用
首先用户构建数据库连接池参数（connectionparam），包括driver、url、user、password必须项，可以自定义minconnection、maxconnection等可选项，如果不设置，则使用系统默认值，这是使用builder构建含有大量属性的好处，其中包括必须属性和可选属性。然后向connectionpoolfactory使用特定的名称注册连接池，最后通过调用connectionpoolfactory静态工厂方法获取connection。
string driver = "com.mysql.jdbc.driver";
string url = "jdbc:mysql://localhost:3306/test";
string user = "root";
string password = "root";
connectionparam connectionparam = new connectionparam.connectionparambuilder(driver, url, user, password).build();
connectionpoolfactory.registerconnectionpool("test", connectionparam);
connection connection = connectionpoolfactory.getconnection("test");
三、代码
.paramconfiguration
package database.config;
import java.io.serializable;
/**
* database connection parameters
* created by michael wong on 2016/1/18.
*/
public class paramconfiguration implements serializable {
public static final int min_connection = 5;
public static final int max_connection = 50;
public static final int min_idle = 5;
public static final long max_wait = 30000;
private paramconfiguration() {}
}
.builder
package database;
/**
* builder
* created by michael wong on 2016/1/18.
*/
public interface builder<t> {
t build();
}
.connectionparam
package database;
import database.config.paramconfiguration;
/**
* database connection parameters
* created by michael wong on 2016/1/18.
*/
public class connectionparam {
private final string driver;
private final string url;
private final string user;
private final string password;
private final int minconnection;
private final int maxconnection;
private final int minidle;
private final long maxwait;
private connectionparam(connectionparambuilder builder) {
this.driver = builder.driver;
this.url = builder.url;
this.user = builder.user;
this.password = builder.password;
this.minconnection = builder.minconnection;
this.maxconnection = builder.maxconnection;
this.minidle = builder.minidle;
this.maxwait = builder.maxwait;
}
public string getdriver() {
return this.driver;
}
public string geturl() {
return this.url;
}
public string getuser() {
return this.user;
}
public string getpassword() {
return this.password;
}
public int getminconnection() {
return this.minconnection;
}
public int getmaxconnection() {
return this.maxconnection;
}
public int getminidle() {
return this.minidle;
}
public long getmaxwait() {
return this.maxwait;
}
public static class connectionparambuilder implements builder<connectionparam> {
// required parameters
private final string driver;
private final string url;
private final string user;
private final string password;
// optional parameters - initialized to default value
private int minconnection = paramconfiguration.min_connection;
private int maxconnection = paramconfiguration.max_connection;
private int minidle = paramconfiguration.min_idle;
// getting connection wait time
private long maxwait = paramconfiguration.max_wait;
public connectionparambuilder(string driver, string url, string user, string password) {
this.driver = driver;
this.url = url;
this.user = user;
this.password = password;
}
public connectionparambuilder minconnection(int minconnection) {
this.minconnection = minconnection;
return this;
}
public connectionparambuilder maxconnection(int maxconnection) {
this.maxconnection = maxconnection;
return this;
}
public connectionparambuilder minidle(int minidle) {
this.minidle = minidle;
return this;
}
public connectionparambuilder maxwait(int maxwait) {
this.maxwait = maxwait;
return this;
}
@override
public connectionparam build() {
return new connectionparam(this);
}
}
}
.connectionpool
package database.factory;
import database.connectionparam;
import javax.sql.datasource;
import java.io.printwriter;
import java.lang.reflect.invocationhandler;
import java.lang.reflect.method;
import java.lang.reflect.proxy;
import java.sql.connection;
import java.sql.drivermanager;
import java.sql.sqlexception;
import java.sql.sqlfeaturenotsupportedexception;
import java.util.vector;
import java.util.concurrent.arrayblockingqueue;
import java.util.concurrent.timeunit;
import java.util.logging.logger;
/**
* connection pool
* created by michael wong on 2016/1/18.
*/
public class connectionpool implements datasource {
private static final int initial_size = 5;
private static final string close_method = "close";
private static logger logger;
private int size;
private connectionparam connectionparam;
private arrayblockingqueue<connection> idleconnectionqueue;
private vector<connection> busyconnectionvector;
protected connectionpool(connectionparam connectionparam) {
this.connectionparam = connectionparam;
int maxconnection = connectionparam.getmaxconnection();
idleconnectionqueue = new arrayblockingqueue<>(maxconnection);
busyconnectionvector = new vector<>();
logger = logger.getlogger(this.getclass().getname());
initconnection();
}
private void initconnection() {
int minconnection = connectionparam.getminconnection();
int initialsize = initial_size < minconnection ? minconnection : initial_size;
try {
class.forname(connectionparam.getdriver());
for (int i = 0; i < initialsize + connectionparam.getminconnection(); i++) {
idleconnectionqueue.put(newconnection());
size++;
}
} catch (exception e) {
throw new exceptionininitializererror(e);
}
}
@override
public connection getconnection() throws sqlexception {
try {
final connection connection = idleconnectionqueue.poll(connectionparam.getmaxwait(), timeunit.milliseconds);
if (connection == null) {
logger.info(emptymsg());
ensurecapacity();
return null;
}
busyconnectionvector.add(connection);
return (connection) proxy.newproxyinstance(this.getclass().getclassloader(),
new class[]{connection.class}, new invocationhandler() {
@override
public object invoke(object proxy, method method, object[] args) throws throwable {
if (!method.getname().equals(close_method)) {
return method.invoke(connection, args);
} else {
idleconnectionqueue.offer(connection);
busyconnectionvector.remove(connection);
return null;
}
}
});
} catch (interruptedexception e) {
e.printstacktrace();
}
return null;
}
private connection newconnection() throws sqlexception {
string url = connectionparam.geturl();
string user = connectionparam.getuser();
string password = connectionparam.getpassword();
return drivermanager.getconnection(url, user, password);
}
protected int size() {
return size;
}
protected int idleconnectionquantity() {
return idleconnectionqueue.size();
}
protected int busyconnectionquantity() {
return busyconnectionvector.size();
}
private void ensurecapacity() throws sqlexception {
int minidle = connectionparam.getminidle();
int maxconnection = connectionparam.getmaxconnection();
int newcapacity = size + minidle;
newcapacity = newcapacity > maxconnection ? maxconnection : newcapacity;
int growcount = 0;
if (size < newcapacity) {
try {
for (int i = 0; i < newcapacity - size; i++) {
idleconnectionqueue.put(newconnection());
growcount++;
}
} catch (interruptedexception e) {
e.printstacktrace();
}
}
size = size + growcount;
}
protected void clear() {
try {
while (size-- > 0) {
connection connection = idleconnectionqueue.take();
connection.close();
}
} catch (interruptedexception | sqlexception e) {
e.printstacktrace();
}
}
private string emptymsg() {
return "database is busy, please wait...";
}
@override
public connection getconnection(string username, string password) throws sqlexception {
return null;
}
@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;
}
@override
public <t> t unwrap(class<t> iface) throws sqlexception {
return null;
}
@override
public boolean iswrapperfor(class<?> iface) throws sqlexception {
return false;
}
}
.connectionpoolfactory
package database.factory;
import database.connectionparam;
import java.sql.connection;
import java.sql.sqlexception;
import java.util.map;
import java.util.concurrent.concurrenthashmap;
/**
* connection pool factory
* created by michael wong on 2016/1/18.
*/
public class connectionpoolfactory {
private connectionpoolfactory() {}
private static map<string, connectionpool> poolmap = new concurrenthashmap<>();
public static connection getconnection(string poolname) throws sqlexception {
namecheck(poolname);
connectionpool connectionpool = poolmap.get(poolname);
return connectionpool.getconnection();
}
public static void registerconnectionpool(string name, connectionparam connectionparam) {
registercheck(name);
poolmap.put(name, new connectionpool(connectionparam));
}
// let gc
public static void unregisterconnectionpool(string name) {
namecheck(name);
final connectionpool connectionpool = poolmap.get(name);
poolmap.remove(name);
new thread(new runnable() {
@override
public void run() {
connectionpool.clear();
}
}).start();
}
public static int size(string poolname) {
namecheck(poolname);
return poolmap.get(poolname).size();
}
public static int getidleconnectionquantity(string poolname) {
namecheck(poolname);
return poolmap.get(poolname).idleconnectionquantity();
}
public static int getbusyconnectionquantity(string poolname) {
namecheck(poolname);
return poolmap.get(poolname).busyconnectionquantity();
}
private static void registercheck(string name) {
if (name == null) {
throw new illegalargumentexception(nullname());
}
}
private static void namecheck(string name) {
if (name == null) {
throw new illegalargumentexception(nullname());
}
if (!poolmap.containskey(name)) {
throw new illegalargumentexception(notexists(name));
}
}
private static string nullname() {
return "pool name must not be null";
}
private static string notexists(string name) {
return "connection pool named " + name + " does not exists";
}
}
四、测试
junit单元测试
package database.factory;
import database.connectionparam;
import org.junit.test;
import java.sql.connection;
import java.sql.sqlexception;
import java.util.arraylist;
import java.util.list;
import static org.junit.assert.*;
/**
* connectionpoolfactory test
* created by michael wong on 2016/1/20.
*/
public class connectionpoolfactorytest {
@test
public void testgetconnection() throws sqlexception {
string driver = "com.mysql.jdbc.driver";
string url = "jdbc:mysql://localhost:3306/test";
string user = "root";
string password = "root";
connectionparam connectionparam = new connectionparam.connectionparambuilder(driver, url, user, password).build();
connectionpoolfactory.registerconnectionpool("test", connectionparam);
list<connection> connectionlist = new arraylist<>();
for(int i = 0; i < 12; i++) {
connectionlist.add(connectionpoolfactory.getconnection("test"));
}
print();
close(connectionlist);
print();
connectionlist.clear();
for(int i = 0; i < 12; i++) {
connectionlist.add(connectionpoolfactory.getconnection("test"));
}
print();
close(connectionlist);
connectionpoolfactory.unregisterconnectionpool("test");
}
@test(expected = illegalargumentexception.class)
public void testexception() {
try {
connectionpoolfactory.getconnection("test");
} catch (sqlexception e) {
e.printstacktrace();
}
}
private void close(list<connection> connectionlist) throws sqlexception {
for(connection conn : connectionlist) {
if (conn != null) {
conn.close();
}
}
}
private void print() {
system.out.println("idle: " + connectionpoolfactory.getidleconnectionquantity("test"));
system.out.println("busy: " + connectionpoolfactory.getbusyconnectionquantity("test"));
system.out.println("size: " + connectionpoolfactory.size("test"));
}
}
以上就是本文的全部内容，希望对大家的学习有所帮助。
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