PostgreSQL JDBC 驱动轮作物双倍价值

Question

I'm using PostgreSql 9.3 together with the postgresql-9.3-1101 JDBC Driver. And there is a really strange behavior with the PreparedStatements .

Here is the example: First I create a test table:

CREATE TABLE double_test
(
   id          numeric(18)     NOT NULL
);

After that that i run following code:

DecimalFormat df = new DecimalFormat("0");
try {
    conn = BeanUtils.getBean("dataSource", DataSource.class).getConnection();
    conn.setAutoCommit(false);
    conn.createStatement().execute("DELETE from double_test ");
    conn.commit();
    PreparedStatement stmt = conn.prepareStatement("INSERT INTO double_test (id )VALUES (?)");
    double input = 1234567890123456d;
    System.out.println("Input:" + df.format(input));
    stmt.setDouble(1, input);
    stmt.execute();
    conn.commit();

    ResultSet rs = conn.createStatement().executeQuery("SELECT id FROM double_test ");
    rs.next();
    System.out.println("Output:" + df.format(rs.getDouble(1)));
    rs.close();
} catch (SQLException e1) {
    throw new RuntimeException(e1);
} finally {
    try {
        conn.close();
    } catch (SQLException e) {
        throw new RuntimeException(e);
    }
}

The output of the code will be:

Input: 1234567890123456
Output:1234567890123460

Which gets me very confused, after the 15. digit the Postgres JDBC Driver starts to round. The inserted data gets corrupted, without any further notice!

Did I miss anything here? Has my code any errors?

Or is this a bug in the Driver? If so, I really wonder that no one noticed this yet.

Maybe working with BigDecimal will prevent the data from corrupting, but this is just a workaround.

Answer 1

There is a two problem.

First from Double class:

System.out.println(0.1 + 0.2); //output 0.30000000000000004

So usually don't use Double (also Float ).

Second from jdbc driver, it is triying to save database with toString method which class related with org.postgresql.jdbc.PgPreparedStatement .

Check this:

System.out.println(new BigDecimal("0.00000072")); // print 7.2E-7

It is equal but when Jdbc driver save with this, some precisions corrupt, so I replace

    public void setBigDecimal(@Positive int parameterIndex, @Nullable BigDecimal x)
            throws SQLException {
        setNumber(parameterIndex, x); // It is using toString method
    }

with this:

public void setBigDecimal(@Positive int parameterIndex, @Nullable BigDecimal x)
        throws SQLException {
    checkClosed();
    if (x == null) {
        setNull(parameterIndex, Types.DECIMAL);
    } else {
        bindLiteral(parameterIndex, x.toPlainString(), Oid.NUMERIC); //now using toPlainString
    }

}

If you really want to use Double or Float you can fix like this changes.