我应该如何将 try-with-resources 与 JDBC 一起使用? [英] How should I use try-with-resources with JDBC?

问题描述

我有一种使用 JDBC 从数据库中获取用户的方法:

I have a method for getting users from a database with JDBC:

public List<User> getUser(int userId) {
    String sql = "SELECT id, name FROM users WHERE id = ?";
    List<User> users = new ArrayList<User>();
    try {
        Connection con = DriverManager.getConnection(myConnectionURL);
        PreparedStatement ps = con.prepareStatement(sql); 
        ps.setInt(1, userId);
        ResultSet rs = ps.executeQuery();
        while(rs.next()) {
            users.add(new User(rs.getInt("id"), rs.getString("name")));
        }
        rs.close();
        ps.close();
        con.close();
    } catch (SQLException e) {
        e.printStackTrace();
    }
    return users;
}

我应该如何使用 Java 7 try-with-resources 改进此代码?

How should I use Java 7 try-with-resources to improve this code?

我已经尝试过下面的代码，但它使用了许多 try 块，并没有大大提高可读性.我应该以另一种方式使用 try-with-resources 吗?

I have tried with the code below, but it uses many try blocks, and doesn't improve the readability much. Should I use try-with-resources in another way?

public List<User> getUser(int userId) {
    String sql = "SELECT id, name FROM users WHERE id = ?";
    List<User> users = new ArrayList<>();
    try {
        try (Connection con = DriverManager.getConnection(myConnectionURL);
             PreparedStatement ps = con.prepareStatement(sql);) {
            ps.setInt(1, userId);
            try (ResultSet rs = ps.executeQuery();) {
                while(rs.next()) {
                    users.add(new User(rs.getInt("id"), rs.getString("name")));
                }
            }
        }
    } catch (SQLException e) {
        e.printStackTrace();
    }
    return users;
}

推荐答案

在你的例子中不需要外部 try，所以你至少可以从 3 降到 2，而且你不需要关闭 ; 在资源列表的末尾.使用两个 try 块的优点是您的所有代码都预先存在，因此您不必引用单独的方法:

There's no need for the outer try in your example, so you can at least go down from 3 to 2, and also you don't need closing ; at the end of the resource list. The advantage of using two try blocks is that all of your code is present up front so you don't have to refer to a separate method:

public List<User> getUser(int userId) {
    String sql = "SELECT id, username FROM users WHERE id = ?";
    List<User> users = new ArrayList<>();
    try (Connection con = DriverManager.getConnection(myConnectionURL);
         PreparedStatement ps = con.prepareStatement(sql)) {
        ps.setInt(1, userId);
        try (ResultSet rs = ps.executeQuery()) {
            while(rs.next()) {
                users.add(new User(rs.getInt("id"), rs.getString("name")));
            }
        }
    } catch (SQLException e) {
        e.printStackTrace();
    }
    return users;
}

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