尝试使用资源 - 参数化 PreparedStatements [重复]答案

【问题标题】：try with resources - parameterized PreparedStatements [duplicate]尝试使用资源 - 参数化 PreparedStatements [重复]
【发布时间】：2018-09-06 18:06:02
【问题描述】：

编辑建议的答案是不可接受的，不能为我所拥有的每种方法声明其他方法，想象一下？。必须有一个嵌套的 try with resources 解决方案。

如何将 try 语句与带有参数的 prepare 语句一起使用？

我有以下两行的错误。

preparedStatement.setString(1, uuid);
preparedStatement.setString(2, emailAddress);

错误声明最终或有效最终变量被执行

public UserBean getUserDevices(final String emailAddress, final String uuid) throws SQLException {
    UserBean userBean = null;

    String query = "SELECT user.id, user.emailAddress, device.uuid, device.active, device.user_id FROM user " +
            "LEFT JOIN device ON user.id = device.user_id AND device.uuid = ? " +
            "WHERE user.emailAddress = ?";

    try (Connection connection = dataSource.getConnection();
         PreparedStatement preparedStatement = connection.prepareStatement(query);
         preparedStatement.setString(1, uuid);
         preparedStatement.setString(2, emailAddress);
         ResultSet resultSet = preparedStatement.executeQuery();

    ) {
        while(resultSet.next()) {
            if(userBean == null) { // initialize user once while iterating for devices
                userBean = new UserBean(resultSet.getInt("user.id"), resultSet.getString("user.emailAddress"), null);
            }
            if(resultSet.getString("device.uuid") != null) { // if device exists (it's a LEFT JOIN) then add
                userBean.getDevices().add(new DeviceBean(0, resultSet.getString("device.uuid"), resultSet.getBoolean("device.active"), resultSet.getInt("device.user_id")));
            }
        }
    }
    return userBean;
}

【问题讨论】：

这两行代码应该在try块里面。不在 try 块前面的括号中。
在实例化实现 Closeable 的类时使用 try-with-resources 的想法。将代码移到 try 块中
resultSet 和preparedStatements 都是可关闭的，我想利用try 资源自动关闭，有没有办法与内外部try 资源一起使用？
我们都告诉了你如何继续。问题是什么？你试过吗？

标签： java prepared-statement

【解决方案1】：

使用inner try with resource，在external try with resource之后，初始化语句，然后使用inner try with resource作为resultSet。

public UserBean getUserDevices(final String emailAddress, final String uuid) throws SQLException {
    UserBean userBean = null;

    String query = "SELECT user.id, user.emailAddress, device.uuid, device.active, device.user_id FROM user " +
            "LEFT JOIN device ON user.id = device.user_id AND device.uuid = ? " +
            "WHERE user.emailAddress = ?";

    try (Connection connection = dataSource.getConnection();
         PreparedStatement preparedStatement = connection.prepareStatement(query);
    ) {
        preparedStatement.setString(1, uuid);
        preparedStatement.setString(2, emailAddress);

        try(ResultSet resultSet = preparedStatement.executeQuery();) {
            while(resultSet.next()) {
                if(userBean == null) { // initialize user once while iterating for devices
                    userBean = new UserBean(resultSet.getInt("user.id"), resultSet.getString("user.emailAddress"), null);
                }
                if(resultSet.getString("device.uuid") != null) { // if device exists (it's a LEFT JOIN) then add
                    userBean.getDevices().add(new DeviceBean(0, resultSet.getString("device.uuid"), resultSet.getBoolean("device.active"), resultSet.getInt("device.user_id")));
                }
            }
        }
    }
    return userBean;
}

【讨论】：