数据库连接池工具类

DBPool.java

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;

/**
 * 数据库连接池类
 * 1. 类加载时需要产生30个数据库连接
 * 2. 提供获取连接方法
 * 3. 能扩容（增加5个连接）
 * 4. 提供归还连接方法
 */
public class DBPool implements DataSource {
    List<Connection> list = new ArrayList<>();

    public DBPool() throws Exception {
        for (int i = 0; i < 30; i++) {
            list.add(DBUtil.getInstance().getConnection());
        }
    }

    @Override
    public Connection getConnection() throws SQLException {
        // 扩容
        if (list.size() == 0) {
            for (int i = 0; i < 5; i++) {
                try {
                    Connection conn = DBUtil.getInstance().getConnection();
                    list.add(conn);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }
        // remove(0)表示弹出集合中第一个元素
        return list.remove(0);
    }

    /**
     * 归还连接
     * @param conn
     * @return true成功 false失败
     */
    public boolean giveBackConn(Connection conn) {
        return list.add(conn);
    }

    @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;
    }
}