Spring jdbc 'select for update'

问题

I have the following method that I use with Spring JDBC

public String getState() {
    String stateLink = template.queryForObject(
            "select state_url from state_scrape_queue where in_use = false ORDER BY scrape_timestamp NULLS FIRST LIMIT 1",
            (result, rowNum) -> {
                return result.getString("state_url");
            });
    return stateLink;
}

I can't find an example of how to do a for update with Spring JDBC. I want in_use to be set to true using for update.

I need to use select for update since this application will be used in a multi-threaded fashion. I don't want more than one thread to get the same row and the way to prevent that is by using select for update

I was able to do this with plain JDBC, here is the question I asked how to do it with plain JDBC

select "for update" with JDBC?

Anyone know how this would be done?

回答1:

This is what I came up with, feel free to recommend improvements

public String getState() throws SQLException {
    String state = null;

    Connection conn = DataSourceUtils.getConnection(template.getDataSource());
    try {
        conn.setAutoCommit(false);

        String[] colNames = { "id", "state_url", "in_use" };
        String query = "select " + Stream.of(colNames).collect(Collectors.joining(", "))
                + " from state_scrape_queue where in_use = false ORDER BY scrape_timestamp NULLS FIRST LIMIT 1 FOR UPDATE";
        System.out.println(query);
        try (Statement stmt = conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE);
                ResultSet rs = stmt.executeQuery(query)) {
            while (rs.next()) {
                // Get the current values, if you need them.
                state = rs.getString(colNames[1]);

                rs.updateBoolean(colNames[2], true);
                rs.updateRow();
                conn.commit();
            }
        }
    } catch (SQLException e) {
        conn.setAutoCommit(true);
        e.printStackTrace();
    } finally {
        conn.setAutoCommit(true);
    }

    return state;
}

来源：https://stackoverflow.com/questions/56350833/spring-jdbc-select-for-update