Creating a Java Scalar UDF Version of the SQL substr Function

Create a Java UDF deployment where the SQL function passes multiple arguments to the Java UDF.

Prerequisites

You are familiar with Java and can compile a .java file. You know where the resulting .class file will reside on the file system.
You are familiar with Interactive SQL. You can connect to the iqdemo database from Interactive SQL, and can issue the START EXTERNAL ENVIRONMENT JAVA command from Interactive SQL.

Task

Place this Java code in a file named MyJavaSubstr:

public class MyJavaSubstr
{
    public static String my_java_substr( String in, int start, int length )
    {
	String rc = null;
	
	if ( start < 1 )
	{
	    start = 1;
	}

	// Convert the SQL start, length to Java start, end.
	start --;  // Java is 0 based, but SQL is one based.
	int endindex = start+length;
	
	try {
	    if ( in != null )
	    {
	        rc = in.substring( start, endindex );
	    }
	} catch ( IndexOutOfBoundsException ex )
	{
	    System.out.println("ScalarTestFunctions:
                my_java_substr("+in+","+start+","+length+") failed");
	    System.out.println(ex);
	}
	return rc;
 }

In Interactive SQL, connect to the iqdemo database.
In Interactive SQL, install the class file onto the server:
INSTALL JAVA NEW FROM FILE '<pathtofile>/MyJavaSubstr.class'

In Interactive SQL, create the function definition:

CREATE or REPLACE FUNCTION java_substr(IN a VARCHAR(255), IN b INT, IN c INT ) 
  RETURNS VARCHAR(255) 
  EXTERNAL NAME 
    'example.MyJavaSubstr.my_java_substr(Ljava/lang/String;II)Ljava/lang/String;' 
  LANGUAGE JAVA

Notice the code snippet Ljava/lang/String;II indicating parameter types String, int, int.

In Interactive SQL, use the Java UDF in a query against the iqdemo database:
select GivenName, java_substr(Surname,1,1) from Customers where lcase(java_substr(Surname,1,1)) = 'a';