概述
因为数据库连接对象的创建比较消耗性能,所以可以在应用程序启动时就在内存中开辟一片空间(集合)存放多个数据库连接对象,后面需要连接时直接从该空间中取而不用新创建;使用完毕后归还连接(将连接重新放回空间),确保连接对象能重复使用。
装饰者模式示例
1、提供一个接口:
// IWaiter
public interface IWaiter {
void service();
}
2、提供该接口的实现:
// Waiter.java
public class Waiter implements IWaiter{
public void service(){
System.out.println("正在服务");
}
}
3、提供一个包装类实现上述接口,构造参数为该接口的实现,具体代码如下:
// WaiterWrapper
public class WaiterWrapper implements IWaiter {
public WaiterWrapper(Waiter waiter) {
this.waiter = waiter;
}
private Waiter waiter;
@Override
public void service() {
System.out.println("服务之前");
waiter.service();
System.out.println("服务之后");
}
}
4、测试:
IWaiter waiter = new WaiterWrapper(new Waiter());
waiter.service();
/*
服务之前
正在服务
服务之后
*/
自己实现一个简单的连接池
通常一个连接使用完毕后我们要调用它的 close 方法关闭它,而这里我们是要让它归还到连接池,这里我们可以通过装饰者模式修改它的 close 方法实现:
// ConnectionWrap
import java.sql.*;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.concurrent.Executor;
public class ConnectionWrap implements Connection {
private Connection connection = null;
private List<Connection> connectionList;
/**
* 构造函数
* @param connection 要装饰的连接
* @param connectionList 连接池储存连接的集合
*/
public ConnectionWrap(Connection connection, List<Connection> connectionList) {
super();
this.connection = connection;
this.connectionList = connectionList;
}
@Override
public void close() throws SQLException {
connectionList.add(connection);
}
@Override
public Statement createStatement() throws SQLException {
return connection.createStatement();
}
@Override
public PreparedStatement prepareStatement(String sql) throws SQLException {
return connection.prepareStatement(sql);
}
@Override
public CallableStatement prepareCall(String sql) throws SQLException {
return connection.prepareCall(sql);
}
@Override
public String nativeSQL(String sql) throws SQLException {
return connection.nativeSQL(sql);
}
@Override
public void setAutoCommit(boolean autoCommit) throws SQLException {
connection.setAutoCommit(autoCommit);
}
@Override
public boolean getAutoCommit() throws SQLException {
return connection.getAutoCommit();
}
@Override
public void commit() throws SQLException {
connection.commit();
}
@Override
public void rollback() throws SQLException {
connection.rollback();
}
@Override
public boolean isClosed() throws SQLException {
return connection.isClosed();
}
@Override
public DatabaseMetaData getMetaData() throws SQLException {
return connection.getMetaData();
}
@Override
public void setReadOnly(boolean readOnly) throws SQLException {
connection.setReadOnly(readOnly);
}
@Override
public boolean isReadOnly() throws SQLException {
return connection.isReadOnly();
}
@Override
public void setCatalog(String catalog) throws SQLException {
connection.setCatalog(catalog);
}
@Override
public String getCatalog() throws SQLException {
return connection.getCatalog();
}
@Override
public void setTransactionIsolation(int level) throws SQLException {
connection.setTransactionIsolation(level);
}
@Override
public int getTransactionIsolation() throws SQLException {
return connection.getTransactionIsolation();
}
@Override
public SQLWarning getWarnings() throws SQLException {
return connection.getWarnings();
}
@Override
public void clearWarnings() throws SQLException {
connection.clearWarnings();
}
@Override
public Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException {
return connection.createStatement(resultSetType, resultSetConcurrency);
}
@Override
public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
return connection.prepareStatement(sql, resultSetType, resultSetConcurrency);
}
@Override
public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
return connection.prepareCall(sql,resultSetType,resultSetConcurrency);
}
@Override
public Map<String, Class<?>> getTypeMap() throws SQLException {
return connection.getTypeMap();
}
@Override
public void setTypeMap(Map<String, Class<?>> map) throws SQLException {
connection.setTypeMap(map);
}
@Override
public void setHoldability(int holdability) throws SQLException {
connection.setHoldability(holdability);
}
@Override
public int getHoldability() throws SQLException {
return connection.getHoldability();
}
@Override
public Savepoint setSavepoint() throws SQLException {
return connection.setSavepoint();
}
@Override
public Savepoint setSavepoint(String name) throws SQLException {
return connection.setSavepoint(name);
}
@Override
public void rollback(Savepoint savepoint) throws SQLException {
connection.rollback();
}
@Override
public void releaseSavepoint(Savepoint savepoint) throws SQLException {
connection.releaseSavepoint(savepoint);
}
@Override
public Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
return connection.createStatement(resultSetType, resultSetConcurrency, resultSetHoldability);
}
@Override
public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
return connection.prepareStatement(sql, resultSetType, resultSetConcurrency, resultSetHoldability);
}
@Override
public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
return connection.prepareCall(sql,resultSetType,resultSetConcurrency,resultSetHoldability);
}
@Override
public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException {
return connection.prepareStatement(sql, autoGeneratedKeys);
}
@Override
public PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException {
return connection.prepareStatement(sql, columnIndexes);
}
@Override
public PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException {
return connection.prepareStatement(sql, columnNames);
}
@Override
public Clob createClob() throws SQLException {
return connection.createClob();
}
@Override
public Blob createBlob() throws SQLException {
return connection.createBlob();
}
@Override
public NClob createNClob() throws SQLException {
return connection.createNClob();
}
@Override
public SQLXML createSQLXML() throws SQLException {
return connection.createSQLXML();
}
@Override
public boolean isValid(int timeout) throws SQLException {
return connection.isValid(timeout);
}
@Override
public void setClientInfo(String name, String value) throws SQLClientInfoException {
connection.setClientInfo(name,value);
}
@Override
public void setClientInfo(Properties properties) throws SQLClientInfoException {
connection.setClientInfo(properties);
}
@Override
public String getClientInfo(String name) throws SQLException {
return connection.getClientInfo(name);
}
@Override
public Properties getClientInfo() throws SQLException {
return connection.getClientInfo();
}
@Override
public Array createArrayOf(String typeName, Object[] elements) throws SQLException {
return connection.createArrayOf(typeName,elements);
}
@Override
public Struct createStruct(String typeName, Object[] attributes) throws SQLException {
return connection.createStruct(typeName,attributes);
}
@Override
public void setSchema(String schema) throws SQLException {
connection.setSchema(schema);
}
@Override
public String getSchema() throws SQLException {
return connection.getSchema();
}
@Override
public void abort(Executor executor) throws SQLException {
connection.abort(executor);
}
@Override
public void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException {
connection.setNetworkTimeout(executor,milliseconds);
}
@Override
public int getNetworkTimeout() throws SQLException {
return connection.getNetworkTimeout();
}
@Override
public <T> T unwrap(Class<T> iface) throws SQLException {
return connection.unwrap(iface);
}
@Override
public boolean isWrapperFor(Class<?> iface) throws SQLException {
return connection.isWrapperFor(iface);
}
}
对于连接池,Java 已经给我们提供了接口 javax.sql.DataSource
,我们要做的就是实现它:
// MyDataSource
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.List;
import java.util.logging.Logger;
public class MyDataSource implements DataSource {
// 定义一个集合用来存放连接
private List<Connection> connections = new ArrayList<>();
public MyDataSource() {
// 初始化 10 个连接
for (int i = 0; i < 10; i++) {
connections.add(JDBCUtil.getConnection());
}
}
/**
* 获取连接
*
* @return 从连接池取出的连接
*/
@Override
public Connection getConnection() throws SQLException {
// 取连接但集合没有连接时,新添加 5 个连接
if (connections.size() == 0) {
for (int i = 0; i < 5; i++) {
connections.add(JDBCUtil.getConnection());
}
}
Connection connection = connections.remove(0);
// 返回我们定义的连接包装类
ConnectionWrap connectionWrap = new ConnectionWrap(connection, connections);
return connectionWrap;
}
...
}
此时就可以通过我们自己编写的连接池获取连接了:
try {
MyDataSource dataSource = new MyDataSource();
Connection connection = dataSource.getConnection();
System.out.println(connection); // com.zze.util.ConnectionWrap@6c629d6e
} catch (SQLException e) {
e.printStackTrace();
}
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