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使用装饰者模式自己实现一个数据库连接池

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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();
}
# Java 杂项  

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