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java的单例模式实现从配置文件获取信息和单例实现mysql的数据库连接池 

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                                        <h5><a id="java_0"></a>java的单例模式实现从配置文件获取信息<button class="cnblogs-toc-button" title="显示目录导航" aria-expanded="false"></button></h5>

package lm;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.Properties;

public class ConfigFile {
	static public Properties p = new Properties();
	private static ConfigFile singleton = null;
	
	static public ConfigFile getInstance() {
		if (singleton == null) {
			synchronized(ConfigFile.class) {
				if (singleton == null) {
					singleton = new ConfigFile();
				}
			}
		}
		return singleton;
	}
	
	public void init(String path) throws FileNotFoundException, IOException {
		p.load(new FileInputStream(path));
	}
	
	
	public String getMysqlUrl() {
		return p.getProperty("MYSQL_URL");
	}
	public String getMYSQL_USER() {
		return p.getProperty("MYSQL_USER");
	}
	public String getMYSQL_PWD() {
		return p.getProperty("MYSQL_PWD");
	}

}
java 单例实现 mysql 的数据库连接池
package lm;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;


import org.apache.log4j.LogManager;
import org.apache.log4j.Logger;


import up.conf.ConfigFile;


public class ConnectionPool {
Logger LOG = LogManager.getLogger(ConnectionPool.class);
static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
String JDBC_DB_URL = ConfigFile.getInstance().getMysqlUrl();


<span class="hljs-title class_">String</span> <span class="hljs-variable constant_">JDBC_USER</span> = <span class="hljs-title class_">ConfigFile</span>.<span class="hljs-title function_">getInstance</span>().<span class="hljs-title function_">getMYSQL_USER</span>();
<span class="hljs-title class_">String</span> <span class="hljs-variable constant_">JDBC_PASS</span> = <span class="hljs-title class_">ConfigFile</span>.<span class="hljs-title function_">getInstance</span>().<span class="hljs-title function_">getMYSQL_PWD</span>();
<span class="hljs-title class_">List</span>&lt;<span class="hljs-title class_">Connection</span>&gt; cs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayList</span>&lt;<span class="hljs-title class_">Connection</span>&gt;();
private <span class="hljs-keyword">static</span> <span class="hljs-title class_">ConnectionPool</span> singleton = <span class="hljs-literal">null</span>;

int size;

<span class="hljs-keyword">static</span> public <span class="hljs-title class_">ConnectionPool</span> <span class="hljs-title function_">getInstance</span>(<span class="hljs-params"></span>) {
	<span class="hljs-keyword">if</span> (singleton == <span class="hljs-literal">null</span>) {
		<span class="hljs-title function_">synchronized</span>(<span class="hljs-params">ConnectionPool.<span class="hljs-keyword">class</span></span>) {
			<span class="hljs-keyword">if</span> (singleton == <span class="hljs-literal">null</span>) {
				singleton = <span class="hljs-keyword">new</span> <span class="hljs-title class_">ConnectionPool</span>(<span class="hljs-number">10</span>);
			}
		}
	}
	<span class="hljs-keyword">return</span> singleton;
}

private <span class="hljs-title class_">ConnectionPool</span>(int size) {
	<span class="hljs-variable language_">this</span>.<span class="hljs-property">size</span> = size;
	<span class="hljs-title function_">init</span>();
}

public <span class="hljs-keyword">void</span> <span class="hljs-title function_">init</span>(<span class="hljs-params"></span>) {
	<span class="hljs-comment">// 这里恰恰不能使用try-with-resource的方式，因为这些连接都需要是"活"的，不要被自动关闭了</span>
	<span class="hljs-keyword">try</span> {
		<span class="hljs-title class_">Class</span>.<span class="hljs-title function_">forName</span>(<span class="hljs-variable constant_">JDBC_DRIVER</span>);
		<span class="hljs-keyword">for</span> (int i = <span class="hljs-number">0</span>; i &lt; size; i++) {
			<span class="hljs-title class_">Connection</span> c = <span class="hljs-title class_">DriverManager</span>.<span class="hljs-title function_">getConnection</span>(<span class="hljs-variable constant_">JDBC_DB_URL</span>,<span class="hljs-variable constant_">JDBC_USER</span>, <span class="hljs-variable constant_">JDBC_PASS</span>);
			<span class="hljs-comment">// System.out.println("完成第"+ ( i + 1 ) +"个连接");</span>
			cs.<span class="hljs-title function_">add</span>(c);
		}
	} <span class="hljs-keyword">catch</span> (<span class="hljs-title class_">ClassNotFoundException</span> e) {
		<span class="hljs-variable constant_">LOG</span>.<span class="hljs-title function_">error</span>(<span class="hljs-string">"init connectPool: "</span>,e);
		<span class="hljs-comment">//System.out.println("init connectPool: " + e.getMessage());</span>
	} <span class="hljs-keyword">catch</span> (<span class="hljs-title class_">SQLException</span> e) {
		<span class="hljs-variable constant_">LOG</span>.<span class="hljs-title function_">error</span>(<span class="hljs-string">"init connectPool: "</span>,e);
		<span class="hljs-comment">//System.out.println("init connectPool: " + e.getMessage());</span>
	}
}

public synchronized <span class="hljs-title class_">Connection</span> <span class="hljs-title function_">getConnection</span>(<span class="hljs-params"></span>) {
	<span class="hljs-keyword">while</span> (cs.<span class="hljs-title function_">isEmpty</span>()) {
		<span class="hljs-keyword">try</span> {
			<span class="hljs-comment">// 如果连接池中没有连接可用则等待</span>
			<span class="hljs-variable language_">this</span>.<span class="hljs-title function_">wait</span>();
		} <span class="hljs-keyword">catch</span> (<span class="hljs-title class_">InterruptedException</span> e) {
			<span class="hljs-comment">//System.out.println("getConnection get error:" + e.getMessage());</span>
			<span class="hljs-variable constant_">LOG</span>.<span class="hljs-title function_">error</span>(<span class="hljs-string">"getConnection get error:"</span>,e);
		}
	}
	<span class="hljs-comment">// 移除第一个连接池</span>
	<span class="hljs-title class_">Connection</span> conn = cs.<span class="hljs-title function_">remove</span>(<span class="hljs-number">0</span>);
	<span class="hljs-keyword">return</span> conn;
}

public synchronized <span class="hljs-keyword">void</span> <span class="hljs-title function_">returnConnection</span>(<span class="hljs-params">Connection c</span>) {
	<span class="hljs-comment">// 使用完给回连接池中</span>
	cs.<span class="hljs-title function_">add</span>(c);
	<span class="hljs-comment">// 唤醒wait告诉它有新的连接池可用</span>
	<span class="hljs-variable language_">this</span>.<span class="hljs-title function_">notifyAll</span>();
}



}