Java, JDBC, and SQL data type conversions

In this section we discuss about the way MySQL and DB2 UDB handles column 

type to Java data type conversions. As we saw in 5.1,  Data type mapping  on 

page 90, MySQL and DB2 UDB have different data types. As you migrate your 

Java application you should check the Java data types used to fetch your data 

using JDBC. The JDBC driver converts the data exchanged between the 

application and the database using the specified schema mapping, which is 

defined by both DB2 UDB and MySQL for their data types.

Table 7 8, shows MySQL to Java data types. Since MySQL does not enforce a 

strict type conversions, the Java programmer has to take care of data loss 

because of round off, overflow, or precision loss.

Table 7 8   MySQL data type mapping to Java data type

MySQL column type

Java type

Description

CHAR, VARCHAR, BLOB, 

java.lang.String, 

All these columns types 

TEXT, ENUM, and SET

java.io.InputStream, 

can be converted to any of 

java.io.Reader, 

these java data types.

java.sql.Blob, 

java.sql.Clob

FLOAT, REAL, DOUBLE 

java.lang.String, 

round off, overflow or loss 

PRECISION, NUMERIC, 

java.lang.Short, 

of precision may occur if 

DECIMAL, TINYINT, 

java.lang.Integer, 

you choose a Java numeric 

SMALLINT, MEDIUMINT, 

java.lang.Long, 

data type that has less 

INTEGER, BIGINT

java.lang.Double, 

precision or capacity than 

java.math.BigDecimal 

the MySQL data type you 

are converting to/from.

DATE, TIME, DATETIME, 

java.lang.String, 

Locale specific data should 

TIMESTAMP

java.sql.Date, 

be handled with care.

java.sql.Timestamp

On the other hand, DB2 UDB sticks to JDBC specification, and provides a default 

and recommended data type mapping as shown in Table 7 9.

Table 7 9   DB2 UDB data types mapping to Java types

DB2 UDB data type

Java type

 Data type description

SMALLINT

short

16 bit signed integer

INTEGER

int

32 bit signed integer

BIGINT

long

64 bit signed integer

REAL

float

Single precision floating 

point

 Chapter 7. Application porting 

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