使用CLOB和VARCHAR2参数从PL / SQL调用Java函数

Question

I'm stuck on a problem with using a java class' static method in an Oracle 11g Database, called via PL/SQL:

I have got a java class that contains a method which looks like the following:

public class OuterClass
{
  public static String WriteIt(String Input1, String Input2, String Input3)
    {
      return "Hello World!";
    }
}

Calling from PL/SQL, I want to pass a CLOB and two VARCHAR2 datatypes as parameters.

My function definition in PL/SQL looks (currently) like this:

 create or replace FUNCTION HelloWorldExample ( p_Input1 CLOB, p_Input2 VARCHAR2, p_Input3 VARCHAR2 ) RETURN CLOB AS LANGUAGE JAVA NAME 'OuterClass.WriteIt(java.lang.String,java.lang.String,java.lang.String) return java.lang.String'; 

It looks like I need to convert the "clob" to a string first, but how can I do that?

Thank you!

Answer 1

Approach 1: Converting at database level

In order to convert clob to string you can use dbms_lob.substr method.

For example:

create table a1(a clob);
insert into a1 values(rpad('a',1000,'b'));
select dbms_lob.substr(a,500,1) from a1;

In your case, you can alter the HelloWorldExample like following:

create or replace FUNCTION HelloWorldExample
(
  p_Input1 VARCHAR2,
  p_Input2 VARCHAR2,
  p_Input3 VARCHAR2
)
   RETURN CLOB
   AS LANGUAGE JAVA
   NAME 'OuterClass.WriteIt(java.lang.String,java.lang.String,java.lang.String) 
   return java.lang.String';

And, while invoking HelloWorldExample you can convert clob to string like following:

declare
   ccol clob;
   outs varchar2(2000);
begin
   select a into ccol from a1;
   outs := HelloWorldExample(dbms_lob.substr(ccol,500,1),'somestr1','somestr2');
   dbms_output.put_line(outs);
end;
/

Approach 2: Converting at application level

Also, you can use Java's Clob type:

create or replace FUNCTION HelloWorldExample
(
  p_Input1 CLOB,
  p_Input2 VARCHAR2,
  p_Input3 VARCHAR2
)
   RETURN CLOB
   AS LANGUAGE JAVA
   NAME 'OuterClass.WriteIt(java.sql.Clob,java.lang.String,java.lang.String) 
   return java.lang.String';

The java program needs to be updated as following:

public class OuterClass
{
  public static String WriteIt(Clob Input1, String Input2, String Input3)
    {
      return input1.getSubString(1,500);
    }
}