Incorrect double values returned from mysql to java

问题

So I was trying to read some double values from mysql to java. I am using a mybatis mapper to read my values and return the value as a map.

When I run my query in sql, my value comes out to be -42295.8451869851 but when I use mybatis to pick the same from a query and put it in a java Hashmap the value changes to {Double@25327}-42295.84518699004 . Why is this anomaly and what can I do to prevent it?

This is the mybatis query line I am using: I am using the class org.apache.ibatis.session.SqlSession;

List<Map<String, Object>> myListMaps =  getSqlSession().selectList(QUERY_NAME, queryParameters);

Edit: After looking at few responses, I realize that I need to somwhow use bigDecimal instead of Double/Float. So I will reframe my question to solve my purpose here. Is there any way to tell mybatis that a certain sql type is to be mapped to BigDecimal instead of Double/Float in a HashMap?

I also have other values being picked up from sql like integer and varchar that are being converted to the required types of integer and string in java automatically and I want them picked as it is. Just need to change the doubles to bigdecimal.

回答1:

This behavior is expected for the floating point number. You can read how the IEEE 754 works https://en.wikipedia.org/wiki/IEEE_754.

But I think there is another issue happening. You say that the number is double (64-bit), but based on the result it look that it gets converted to float(32-bit)

-42295.8451869851 -> 0xC0E4A6FB0BC59380 (64bit) - 0xC72537D8 (32bit)

-42295.84518699004 -> 0xC0E4A6FB0BC59627 (64bit)- 0xC72537D8 (32bit)

If you want to keep the precision correct then you need to define it correctly both in DB and then in Java use https://docs.oracle.com/javase/8/docs/api/java/math/BigDecimal.html

回答2:

Use BigDecimal if you need precision doc.

来源：https://stackoverflow.com/questions/63841429/incorrect-double-values-returned-from-mysql-to-java

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java

mysql

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MyBatis