Java and ColdFusion data type conversions



ColdFusion does not use explicit types for variables, while Java is strongly typed. However, ColdFusion data does use underlying Java types to represent data.

Under most situations, when the method names are not ambiguous, ColdFusion can determine the data types that a Java object requires, and often it can convert ColdFusion data to the required types. For example, ColdFusion text strings are implicitly converted to the Java String type. Similarly, if a Java object contains a doIt method that expects a parameter of type int, and CFML is issuing a doIt call with a CFML variable x that contains an integer value, ColdFusion converts the variable x to Java int type. However, ambiguous situations can result from Java method overloading, where a class has multiple implementations of the same method that differ only in their parameter types.

Default data type conversion

Whenever possible, ColdFusion automatically matches Java types to ColdFusion types.

The following table lists how ColdFusion converts ColdFusion data values to Java data types when passing arguments. The left column represents the underlying ColdFusion representation of its data. The right column indicates the Java data types into which ColdFusion can automatically convert the data:

CFML

Java

Integer

short, int, long (short and int can result in a loss of precision).

Real number

float double (float can result in a loss of precision.

Boolean

boolean

Date-time

java.util.Date

String, including lists

String

short, int, long, float, double, java.util.Date, when a CFML string represents a number or date.

boolean, for strings with the value Yes, No, True, and False (case-insensitive).

Array

java.util.Vector (ColdFusion Arrays are internally represented using an instance of a java.util.Vector object.)

ColdFusion can also map a CFML array to any of the following when the CFML array contains consistent data of a type that can be converted to the data type of the Java arr: byte[], char[], boolean[], int[], long[], float[], double[], String[], or Object[]. When a CFML array contains data of different of types, the conversion to a simple array type could fail.

Structure

java.util.Map

Query object

java.util.Map

XML document object

Not supported.

ColdFusion component

Not applicable.

The following table lists how ColdFusion converts data returned by Java methods to ColdFusion data types:

Java

CFML

boolean/Boolean

Boolean

byte/Byte

String

char/Char

String

short/Short

Integer

int/Integer

Integer

long/Long

Integer

float/Float

Real Number

double/Double

Real Number

String

String

java.util.Date

Date-time

java.util.List

Comma-delimited list

byte[]

Array

char[]

Array

boolean[]

Array

String[]

Array

java.util.Vector

Array

java.util.Map

Structure

Resolving ambiguous data types with the JavaCast function

You can overload Java methods so a class can have several identically named methods. At runtime, the JVM resolves the specific method to use based on the parameters passed in the call and their types.

In the section The Employee class, the Employee class has two implementations for the SetJobGrade method. One method takes a string variable, the other an integer. If you write code such as the following, which implementation to use is ambiguous:

<cfset emp.SetJobGrade("1")>

The “1” could be interpreted as a string or as a number, so no way exists to know which method implementation to use. When ColdFusion encounters such an ambiguity, it throws a user exception.

The ColdFusion JavaCast function helps you resolve such issues by specifying the Java type of a variable, as in the following line: 

<cfset emp.SetJobGrade(JavaCast("int", "1"))>

The JavaCast function takes two parameters: a string representing the Java data type, and the variable whose type you are setting. You can specify the following Java data types: boolean, int, long, float, double, and String.

For more information about the JavaCast function, see the CFML Reference.