an't infer the SQL type to use for an instance of java.util.ArrayList. Use setObject() with an explicit Types value to specify the type to use.

这个错误通常出现在使用JDBC连接数据库时，无法确定一个Java ArrayList对象对应的SQL类型。解决这个问题的方法是，在使用PreparedStatement时，显式地指定参数的SQL类型，可以使用setObject(int parameterIndex, Object x, int targetSqlType)方法。例如，如果你想将一个ArrayList<String>对象插入到数据库中，可以使用以下代码：

PreparedStatement ps = conn.prepareStatement("INSERT INTO my_table (my_column) VALUES (?)");
ArrayList<String> myList = new ArrayList<>();
// add some values to the list
ps.setObject(1, myList, Types.ARRAY);
ps.execute();

这里使用了Types.ARRAY来指定ArrayList对应的SQL数组类型。你也可以根据需要选择其他类型，比如Types.VARCHAR等。

相关问题

In Java 7, it is possible to write ArrayList<>, for example, with no type specified for the elements. Give an example of a situation in which this is allowed and explain why it is allowed?

In Java 7 and later versions, it is possible to use the diamond operator `<>` to specify the type of a generic class with the type inference feature. For example, instead of writing `ArrayList<String>`, we can write `new ArrayList<>()` and the compiler will infer that it is an `ArrayList<String>` based on the context.

Here is an example of how the diamond operator can be used:

List<String> list = new ArrayList<>();
list.add("apple");
list.add("banana");
List<String> copy = new ArrayList<>(list); // diamond operator used for type inference

In this example, the `ArrayList` constructor is called with no type specified for the elements. However, the compiler is able to infer the type of the `ArrayList` based on the type of the `list` variable, which is a `List<String>`. Therefore, the `copy` variable is also inferred to be a `List<String>`.

The diamond operator is allowed in situations where the type of the generic class can be inferred from the context. This includes cases where the type is specified in the variable declaration or method signature, or where the generic class is being used in a method call with an argument of a specific type. By allowing the diamond operator, Java reduces the amount of boilerplate code needed to use generic classes and makes the code more concise and readable.

Reason: With an unknown wire type, it is no longer possible to infer the data length, so the subsequent data can no longer be interpreted.翻译

原因：使用未知的 Wire Type 就无法推断数据的长度，因此后续的数据就无法解析。这句话的意思是，如果使用未知的 Wire Type，那么就无法确定数据的类型和长度信息，从而无法正确地解析后续的数据。在数据传输过程中，正确地解析数据是非常重要的，否则就会导致数据传输的错误和不可预测的结果。因此，在使用数据传输协议时，必须确保使用已知的 Wire Type，以便能够正确地解析数据的类型和长度信息，从而保证数据传输的正确性和可靠性。