如何在不创建表的情况下从 mysql 列定义中获取 java.sql.Types？

Question

goal

Get java.sql.Types without creating table.

detail

If I define a column like this " a JSON DEFAULT NULL"

How can I get java.sql.Types about column 'a'?

what I have tried

I use jdbc, so I use connection.getMetaData().getTypeInfo to get all types

    public static Map<String, Integer> load(final DatabaseMetaData databaseMetaData) throws SQLException {
    Map<String, Integer> result = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
    try (ResultSet resultSet = databaseMetaData.getTypeInfo()) {
        while (resultSet.next()) {
            result.put(resultSet.getString("TYPE_NAME"), resultSet.getInt("DATA_TYPE"));
        }
    }
    return result;
}

Then I get this map like this

BIGINT -> {Integer@5274} -5

BIGINT UNSIGNED -> {Integer@5274} -5

And so on.

But there is no JSON.

what's more?

If I define like this

"id_card LONG CHAR VARYING"

Then how can I get the java.sql.Types?

Answer 1

The code that you are using looks to be the correct way to get the supported column types.

One possible explanation for your not seeing JSON in the output is that your database does not support JSON as a column type. For instance, although MySQL 8.x supports the JSON data type, according to the manual MySQL 5.6 does not support it.

It could also be the database driver. For instance, I don't know what would happen vis a vis JSON support if you tried to use a Connector/J 5.1 driver with a MySQL 8.x database.

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UPDATE

I had a look at the source code MySQL Connector/J 8.x (latest), and I think that the reason that you can't see JSON is... it is a bug in the JDBC driver.

Looking at the implementation class for DatabaseMetadata , at line 4012 (or thereabouts) we see that the getTypeInfo() has code that assembles a ResultSet for a hard-wired list of types. The JSON type is not there, and there is a comment that says:

  // TODO add missed types (aliases)

(FWIW, I couldn't see any logic in the driver to check which data types are actually supported by the database. That is potentially another bug.)

So, my "possible explanations" (see above) were not the actual explanation in your particular case.

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Solution? I don't think there is a good one in this case. But I recommend that you submit a bug report . (I couldn't find an existing bug report for this particular issue, though there were some old bugs about missing types in MySQL Connector/J 5.x)