归还连接——适配器设计模式

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class DataSourceDemo {

    public static void main(String[] args) throws SQLException {
        //1、创建连接池对象
        JdbcDemo jd = new JdbcDemo();
        System.out.println("使用之前的连接池数量：" + jd.getSize());
        //2、通过连接池对象获取连接对象
        Connection con = jd.getConnection();
        //3、预编译查询语句
        String sql = "select * from users";
        PreparedStatement ps = con.prepareStatement(sql);
        //4、执行sql，获取结果集
        ResultSet rs = ps.executeQuery();
        //5、处理结果集
        while (rs.next()) {
            System.out.println(rs.getInt("id") + "\t" + rs.getString("name") + "\t" + rs.getInt("age"));
        }
        //6、释放资源
        rs.close();
        ps.close();
        con.close();

        System.out.println("使用之后的连接池数量：" + jd.getSize());
    }

}

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.Collections;
import java.util.List;
import java.util.logging.Logger;

/**
 * 自定义数据库连接池
 */
public class JdbcDemo implements DataSource {

    //1、准备容器，用于保存连接对象。因为list是线程不安全的，使用Collections.synchronizedList变成线程安全的对象
    private static List<Connection> pool = Collections.synchronizedList(new ArrayList<>());

    //2、定义静态代码块，通过工具类生成10个连接池对象
    static {
        for (int i = 0; i < 10; i++) {
            Connection connection = JDBCUtils.getConnection();
            pool.add(connection);
        }
    }

    //3、获取一个连接对象
    @Override
    public Connection getConnection() throws SQLException {
        //判断连接池有没有连接对象，如果有，删除0索引上的对象，获取这个从集合中删除的连接对象，这样就可以获取到一个连接对象
        if (pool.size() > 0) {
            Connection con = pool.remove(0);
            //方式1、通过自定义对象对原来的对象进行包装（装饰设计模式）
            //MyConnection mc = new MyConnection(con,pool);
            //返回自定义的连接对象
            //return mc;

            //方式2、使用继承的适配器类
            MyConnection1 mc1 = new MyConnection1(con,pool);
            return mc1;
        } else {
            throw new RuntimeException("连接已用完");
        }
    }

    //4、定义getSize方法，获取连接池容器大小，通过该方法可以获取连接池剩余数量
    public int getSize(){
        return pool.size();
    }

    @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;
    }
}

import java.io.InputStream;
import java.sql.*;
import java.util.Properties;

/**
 * JDBC工具类
 */
public class JDBCUtils {

    //1、构造方法私有化，工具类方法应该使用静态方法
    private JDBCUtils() {
    }

    //2、声明所需的配置变量
    private static String driverClass;    //注册驱动的信息
    private static String url;            //MySQL的地址
    private static String username;       //MySQL用户名
    private static String password;       //MySQL密码

    private static Connection con;

    //3、提供静态代码块，读取配置文件的信息，注册驱动
    static {
        try {
            //读取配置文件的信息为变量赋值(配置文件保存在src下，通过类加载器方式获取配置文件)
            InputStream is = JDBCUtils.class.getClassLoader().getResourceAsStream("config.properties");
            Properties prop = new Properties();
            prop.load(is);

            //赋值
            driverClass = prop.getProperty("driverClass");
            url = prop.getProperty("url");
            username = prop.getProperty("username");
            password = prop.getProperty("password");

            //注册驱动
            Class.forName(driverClass);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    //4、提供获取数据库连接方法
    public static Connection getConnection() {
        try {
            con = DriverManager.getConnection(url, username, password);
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
        return con;
    }

    //5、提供释放资源方法
    public static void close(Connection con, Statement stst, ResultSet rs) {
        if (con != null) {
            try {
                con.close();
            } catch (SQLException e) {
                throw new RuntimeException(e);
            }
        }
        if (stst != null) {
            try {
                stst.close();
            } catch (SQLException e) {
                throw new RuntimeException(e);
            }
        }
        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException e) {
                throw new RuntimeException(e);
            }
        }
    }
}

/**
 * 步骤
 * 1、定义一个类继承适配器类
 * 2、定义连接池对象和连接对象
 * 3、定义有参构造方法为连接池对象和连接对象赋值
 * 4、重写close方法，完成归还连接
 */

//1、继承适配器类
public class MyConnection1 extends MyAdapter {

    //2、定义连接池对象和连接对象
    private Connection con;
    private List<Connection> list;

    //3、定义有参构造方法为连接池对象和连接对象赋值
    public MyConnection1(Connection con, List<Connection> list) {
        super(con);
        this.con = con;
        this.list = list;
    }

    //4、重写close方法，将连接对象归还到连接池
    @Override
    public void close() throws SQLException {
        list.add(con);
    }
}

/**
 * 适配器类（中间类,一般都是抽象类，可以有普通方法，也可以有抽象方法，还可以有构造方法）
 * 实现Connection接口，重写除了close之外的方法
 */
public abstract class MyAdapter implements Connection {
    //定义连接对象
    private Connection con;

    //定义有参构造方法为连接对象赋值
    public MyAdapter(Connection con) {
        this.con = con;
    }

    //5、下面其他的重写方法还是调用原来的方法，功能不变
    @Override
    public Statement createStatement() throws SQLException {
        return con.createStatement();
    }

    @Override
    public PreparedStatement prepareStatement(String sql) throws SQLException {
        return con.prepareStatement(sql);
    }

    @Override
    public CallableStatement prepareCall(String sql) throws SQLException {
        return con.prepareCall(sql);
    }

    @Override
    public String nativeSQL(String sql) throws SQLException {
        return con.nativeSQL(sql);
    }

    @Override
    public void setAutoCommit(boolean autoCommit) throws SQLException {
        con.setAutoCommit(autoCommit);
    }

    @Override
    public boolean getAutoCommit() throws SQLException {
        return con.getAutoCommit();
    }

    @Override
    public void commit() throws SQLException {
        con.commit();
    }

    @Override
    public void rollback() throws SQLException {
        con.rollback();
    }

    @Override
    public boolean isClosed() throws SQLException {
        return con.isClosed();
    }

    @Override
    public DatabaseMetaData getMetaData() throws SQLException {
        return con.getMetaData();
    }

    @Override
    public void setReadOnly(boolean readOnly) throws SQLException {
        con.setReadOnly(readOnly);
    }

    @Override
    public boolean isReadOnly() throws SQLException {
        return con.isReadOnly();
    }

    @Override
    public void setCatalog(String catalog) throws SQLException {
        con.setCatalog(catalog);
    }

    @Override
    public String getCatalog() throws SQLException {
        return con.getCatalog();
    }

    @Override
    public void setTransactionIsolation(int level) throws SQLException {
        con.setTransactionIsolation(level);
    }

    @Override
    public int getTransactionIsolation() throws SQLException {
        return con.getTransactionIsolation();
    }

    @Override
    public SQLWarning getWarnings() throws SQLException {
        return con.getWarnings();
    }

    @Override
    public void clearWarnings() throws SQLException {
        con.clearWarnings();
    }

    @Override
    public Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException {
        return con.createStatement(resultSetType, resultSetConcurrency);
    }

    @Override
    public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
        return con.prepareStatement(sql, resultSetType, resultSetConcurrency);
    }

    @Override
    public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
        return con.prepareCall(sql, resultSetType, resultSetConcurrency);
    }

    @Override
    public Map<String, Class<?>> getTypeMap() throws SQLException {
        return con.getTypeMap();
    }

    @Override
    public void setTypeMap(Map<String, Class<?>> map) throws SQLException {
        con.setTypeMap(map);
    }

    @Override
    public void setHoldability(int holdability) throws SQLException {
        con.setHoldability(holdability);
    }

    @Override
    public int getHoldability() throws SQLException {
        return con.getHoldability();
    }

    @Override
    public Savepoint setSavepoint() throws SQLException {
        return con.setSavepoint();
    }

    @Override
    public Savepoint setSavepoint(String name) throws SQLException {
        return con.setSavepoint(name);
    }

    @Override
    public void rollback(Savepoint savepoint) throws SQLException {
        con.rollback();
    }

    @Override
    public void releaseSavepoint(Savepoint savepoint) throws SQLException {
        con.releaseSavepoint(savepoint);
    }

    @Override
    public Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
        return con.createStatement(resultSetType, resultSetConcurrency);
    }

    @Override
    public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
        return con.prepareStatement(sql, resultSetType, resultSetConcurrency);
    }

    @Override
    public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
        return con.prepareCall(sql, resultSetType, resultSetConcurrency);
    }

    @Override
    public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException {
        return con.prepareStatement(sql, autoGeneratedKeys);
    }

    @Override
    public PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException {
        return con.prepareStatement(sql, columnIndexes);
    }

    @Override
    public PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException {
        return con.prepareStatement(sql, columnNames);
    }

    @Override
    public Clob createClob() throws SQLException {
        return con.createClob();
    }

    @Override
    public Blob createBlob() throws SQLException {
        return con.createBlob();
    }

    @Override
    public NClob createNClob() throws SQLException {
        return con.createNClob();
    }

    @Override
    public SQLXML createSQLXML() throws SQLException {
        return con.createSQLXML();
    }

    @Override
    public boolean isValid(int timeout) throws SQLException {
        return con.isValid(timeout);
    }

    @Override
    public void setClientInfo(String name, String value) throws SQLClientInfoException {
        con.setClientInfo(name, value);
    }

    @Override
    public void setClientInfo(Properties properties) throws SQLClientInfoException {
        con.setClientInfo(properties);
    }

    @Override
    public String getClientInfo(String name) throws SQLException {
        return con.getClientInfo(name);
    }

    @Override
    public Properties getClientInfo() throws SQLException {
        return con.getClientInfo();
    }

    @Override
    public Array createArrayOf(String typeName, Object[] elements) throws SQLException {
        return con.createArrayOf(typeName, elements);
    }

    @Override
    public Struct createStruct(String typeName, Object[] attributes) throws SQLException {
        return con.createStruct(typeName, attributes);
    }

    @Override
    public void setSchema(String schema) throws SQLException {
        con.setSchema(schema);
    }

    @Override
    public String getSchema() throws SQLException {
        return con.getSchema();
    }

    @Override
    public void abort(Executor executor) throws SQLException {
        con.abort(executor);
    }

    @Override
    public void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException {
        con.setNetworkTimeout(executor, milliseconds);
    }

    @Override
    public int getNetworkTimeout() throws SQLException {
        return con.getNetworkTimeout();
    }

    @Override
    public <T> T unwrap(Class<T> iface) throws SQLException {
        return con.unwrap(iface);
    }

    @Override
    public boolean isWrapperFor(Class<?> iface) throws SQLException {
        return con.isWrapperFor(iface);
    }
}