Java finally关键字详解：掌握资源释放与异常处理的最佳实践

Connection conn = null; try {

conn = dataSource.getConnection();
// 执行数据库操作

} catch (SQLException e) {

// 异常处理

} finally {

if (conn != null) {
    try {
        conn.close();
    } catch (SQLException e) {
        // 日志记录
    }
}

}

public int testReturn() {

try {
    System.out.println("try block");
    return 1;
} finally {
    System.out.println("finally block");
    return 2;
}

}

FileInputStream fis = null; try {

fis = new FileInputStream("app.log");
// 处理文件内容

} catch (IOException e) {

System.out.println("文件读取失败");

} finally {

if (fis != null) {
    try {
        fis.close();
    } catch (IOException e) {
        System.out.println("文件关闭异常");
    }
}

}

FileInputStream fis = null; Connection conn = null; HttpURLConnection httpConn = null;

try {

fis = new FileInputStream("data.txt");
// 文件处理逻辑

try {
    conn = dataSource.getConnection();
    // 数据库操作
    
    try {
        httpConn = (HttpURLConnection) new URL("http://api.service.com").openConnection();
        // 网络请求
    } finally {
        if (httpConn != null) {
            httpConn.disconnect();
        }
    }
} finally {
    if (conn != null) {
        try {
            conn.close();
        } catch (SQLException e) {
            System.out.println("数据库连接关闭异常");
        }
    }
}

} catch (Exception e) {

System.out.println("处理过程异常");

} finally {

if (fis != null) {
    try {
        fis.close();
    } catch (IOException e) {
        System.out.println("文件流关闭异常");
    }
}

}

public boolean processOrder(Order order) {

Connection conn = null;
boolean success = false;

try {
    conn = dataSource.getConnection();
    conn.setAutoCommit(false);
    
    // 扣减库存
    reduceInventory(conn, order.getItems());
    // 创建订单记录
    createOrderRecord(conn, order);
    // 生成支付流水
    createPaymentFlow(conn, order);
    
    conn.commit();
    success = true;
    
} catch (SQLException e) {
    if (conn != null) {
        try {
            conn.rollback();
        } catch (SQLException ex) {
            log.error("回滚失败", ex);
        }
    }
    log.error("订单处理异常", e);
} finally {
    if (conn != null) {
        try {
            conn.setAutoCommit(true);
            conn.close();
        } catch (SQLException e) {
            log.error("连接关闭异常", e);
        }
    }
}

return success;

}

// 脆弱的写法 try {

acquireLock();
doBusiness();

} catch (Exception e) {

releaseLock(); // 如果发生Error，锁不会释放
throw e;

}

// 健壮的写法
try {

acquireLock();
doBusiness();

} finally {

releaseLock(); // 无论发生什么，锁都会释放

}