使用数据库连接池优化程序性能
直接获取链接缺点
性能的优化
编写数据库连接池
-
编写连接池需事先java.sql.DataSource接口。DateSource接口中定义了两个重载的getConnection方法：
Connection getConnection()
Connection getConnection(String username,String password) -
实现DataSource接口，并实现连接池功能的步骤：
- 在DataSource构造函数中批量创建与数据库的连接，并把创建的连接加入LinkedList对象中；
- 实现getConnection方法，让getConnection方法每次调用时，从LinkedList中取一个Connection返回给用户；
- 当用户使用完Connection，调用Connection.close方法时，Connection对象应保证将自己返回到LinkedList中，而不要把Conn还给数据库。
难点：Connection保证将自己返回到LinkedList中
演示
1. 建一个JdbcPool类，实现DataSource接口，里面我都有写较为详细的注释。
package cn.itcast.utils;
import javax.sql.DataSource;
import java.io.PrintWriter;
import java.sql.*;
import java.util.LinkedList;
import java.util.Map;
import java.util.Properties;
import java.util.concurrent.Executor;
import java.util.logging.Logger;
/**
* Created by yvettee on 2017/9/28.
*/
public class JdbcPool implements DataSource {
private static LinkedList<Connection> list = new LinkedList<Connection>();
private static Properties prop = new Properties();
//初始化时，要找连接池要一批链接的操作做一次就够
static {
try {
prop.load(JdbcPool.class.getClassLoader().getResourceAsStream("db.properties"));
Class.forName(prop.getProperty("driver"));
//一上来就要10个连接
for (int i = 0; i < 10; i++) {
Connection conn = DriverManager.getConnection(prop.getProperty("url"), prop.getProperty("username"), prop.getProperty("password"));
list.add(conn);
}
} catch (Exception e) {
throw new ExceptionInInitializerError(e);
}
}
@Override
public Connection getConnection() throws SQLException {
if (list.size() <= 0) {
throw new RuntimeException("数据库忙，请稍后再来！");
}
//（链表）始终把第一个链接拿走
Connection conn = list.removeFirst();
// conn.close();这里不能直接关闭，因为会把链接还给数据库，
// 我们的目的是从池里拿链接，也要还给池里
MyConnection my = new MyConnection(conn);
/*
在实际开发，发现对象的方法满足不了开发需求时，有以下几种方法：
1.写一个connection子类，覆盖并增强close方法（不可用）
2.用包装设计模式（这里采用这个）
3.用动态代理
*/
return my;
}
//包装模式，1.实现与被增强对象的相同接口
class MyConnection implements Connection {
//2.在类中定义一个变量，记住被增强对象
private Connection conn;
//3.定义一个构造函数
public MyConnection(Connection conn) {
this.conn = conn;
}
//4.覆盖想增强的方法
public void close() {
list.add(this.conn);
}
@Override
public Statement createStatement() throws SQLException {
//5.对于不想增强的方法，直接调用目标对象（被增强对象）的方法
return this.conn.createStatement();
}
@Override
public PreparedStatement prepareStatement(String sql) throws SQLException {
return null;
}
@Override
public CallableStatement prepareCall(String sql) throws SQLException {
return null;
}
@Override
public String nativeSQL(String sql) throws SQLException {
return null;
}
@Override
public void setAutoCommit(boolean autoCommit) throws SQLException {
}
@Override
public boolean getAutoCommit() throws SQLException {
return false;
}
@Override
public void commit() throws SQLException {
}
@Override
public void rollback() throws SQLException {
}
@Override
public boolean isClosed() throws SQLException {
return false;
}
@Override
public DatabaseMetaData getMetaData() throws SQLException {
return null;
}
@Override
public void setReadOnly(boolean readOnly) throws SQLException {
}
@Override
public boolean isReadOnly() throws SQLException {
return false;
}
@Override
public void setCatalog(String catalog) throws SQLException {
}
@Override
public String getCatalog() throws SQLException {
return null;
}
@Override
public void setTransactionIsolation(int level) throws SQLException {
}
@Override
public int getTransactionIsolation() throws SQLException {
return 0;
}
@Override
public SQLWarning getWarnings() throws SQLException {
return null;
}
@Override
public void clearWarnings() throws SQLException {
this.conn.clearWarnings();
}
@Override
public Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException {
return null;
}
@Override
public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
return null;
}
@Override
public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
return null;
}
@Override
public Map<String, Class<?>> getTypeMap() throws SQLException {
return null;
}
@Override
public void setTypeMap(Map<String, Class<?>> map) throws SQLException {
}
@Override
public void setHoldability(int holdability) throws SQLException {
}
@Override
public int getHoldability() throws SQLException {
return 0;
}
@Override
public Savepoint setSavepoint() throws SQLException {
return null;
}
@Override
public Savepoint setSavepoint(String name) throws SQLException {
return null;
}
@Override
public void rollback(Savepoint savepoint) throws SQLException {
}
@Override
public void releaseSavepoint(Savepoint savepoint) throws SQLException {
}
@Override
public Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
return null;
}
@Override
public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
return null;
}
@Override
public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
return null;
}
@Override
public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException {
return null;
}
@Override
public PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException {
return null;
}
@Override
public PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException {
return null;
}
@Override
public Clob createClob() throws SQLException {
return null;
}
@Override
public Blob createBlob() throws SQLException {
return null;
}
@Override
public NClob createNClob() throws SQLException {
return null;
}
@Override
public SQLXML createSQLXML() throws SQLException {
return null;
}
@Override
public boolean isValid(int timeout) throws SQLException {
return false;
}
@Override
public void setClientInfo(String name, String value) throws SQLClientInfoException {
}
@Override
public void setClientInfo(Properties properties) throws SQLClientInfoException {
}
@Override
public String getClientInfo(String name) throws SQLException {
return null;
}
@Override
public Properties getClientInfo() throws SQLException {
return null;
}
@Override
public Array createArrayOf(String typeName, Object[] elements) throws SQLException {
return null;
}
@Override
public Struct createStruct(String typeName, Object[] attributes) throws SQLException {
return null;
}
@Override
public void setSchema(String schema) throws SQLException {
}
@Override
public String getSchema() throws SQLException {
return null;
}
@Override
public void abort(Executor executor) throws SQLException {
}
@Override
public void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException {
}
@Override
public int getNetworkTimeout() throws SQLException {
return 0;
}
@Override
public <T> T unwrap(Class<T> iface) throws SQLException {
return null;
}
@Override
public boolean isWrapperFor(Class<?> iface) throws SQLException {
return false;
}
}
@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;
}
}
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