Access Web service from Oracle stored procedure

Question

Is there anybody who has successfully accessed a Web service from an Oracle stored procedure? If so, was it a Java stored procedure? A PL/SQL stored procedure?

Is there any reason why I should not be trying to access a WS from a stored proc?

Here are a couple refs that I found so far

• Database Web Services
• Calling external Web Service from a Java Stored Procedure

..Just to clarify, this is for SOAP calls

Answer 1

First off, what sort of web service are you calling? I am assuming either SOAP or REST.

For REST web services, UTL_HTTP is often more than sufficient, combined with a bit of XPath in a simple PL/SQL stored procedure.

For SOAP web services, it depends on how sophisticated you need (or want) to be. You can certainly use XQuery to create an XML document that meets the spec for the web service, use UTL_HTTP to post the document and get the response, and then use some XPath to parse the response all in PL/SQL. This is a relatively manual and relatively brute-force solution, but if you are talking about a handful of web services, it involves a minimum of infrastructure and the calls can get knocked together pretty quickly.

If you expect the calls to evolve over time or you expect there to be a number of procedures calling a number of web services, it probably makes sense to invest time in something like UTL_DBWS (this isn't something, though, that you generally get working in a couple hours).

Answer 2

It's fairly simple to wrap UTL_HTTP in a convenience function:

FUNCTION post
(
    p_url     IN VARCHAR2,
    p_data    IN CLOB,
    p_timeout IN BINARY_INTEGER DEFAULT 60
) 
    RETURN CLOB
IS
    --
    v_request  utl_http.req;
    v_response utl_http.resp;
    v_buffer   CLOB;
    v_chunk    VARCHAR2(4000);
    v_length   NUMBER;
    v_index    NUMBER;
BEGIN

    v_index := 1;
    v_length := nvl(length(p_data), 0);

    -- configure HTTP
    utl_http.set_response_error_check(enable => FALSE);
    utl_http.set_detailed_excp_support(enable => FALSE);
    utl_http.set_transfer_timeout(p_timeout);

    -- send request
    v_request := utl_http.begin_request(p_url, 'POST','HTTP/1.0');
    utl_http.set_header(v_request, 'Content-Type', 'text/xml');
    utl_http.set_header(v_request, 'Content-Length', v_length);
    WHILE v_index <= v_length LOOP
        utl_http.write_text(v_request, substr(p_data, v_index, 4000));
        v_index := v_index + 4000;
    END LOOP;

    -- check HTTP status code for error
    IF v_response.status_code <> utl_http.http_ok THEN   
        raise_application_error(
            cn_http_error,
            v_response.status_code || ' - ' || v_response.reason_phrase
        );
    END IF;

    -- get response
    dbms_lob.createtemporary(v_buffer, FALSE);
    v_response := utl_http.get_response(v_request);
    BEGIN
        LOOP
            utl_http.read_text(v_response, v_chunk, 4000);
            dbms_lob.writeappend(v_buffer, length(v_chunk), v_chunk);
        END LOOP;
    EXCEPTION
        WHEN utl_http.end_of_body THEN NULL;
    END;
    utl_http.end_response(v_response);

    RETURN v_buffer;

END;

Then you just need something to POST a SOAP envelope:

FUNCTION invoke
(
    p_url IN VARCHAR2,
    p_method IN XMLTYPE,
    p_timeout IN NUMBER := 60
)
    RETURN XMLTYPE
IS
    -- calls the given SOAP service
    cn_procedure_name CONSTANT VARCHAR2(30) := 'invoke';
    --
    v_envelope XMLTYPE;
    v_response CLOB;
    v_fault XMLTYPE;
    v_sqlerrm VARCHAR2(2000);
BEGIN

    -- wrap method in SOAP envelope
    SELECT
        XMLElement(
            "soap:Envelope",
            XMLAttributes(
                'http://schemas.xmlsoap.org/soap/envelope/' AS "xmlns:soap"
            ),
            XMLElement(
                "soap:Body",
                p_method
            )
        )
    INTO
        v_envelope
    FROM
        dual;

    -- POST request
    v_response := post(
        p_url,
        '<?xml version="1.0" encoding="ISO-8859-1"?>' || chr(10) || v_envelope.getClobVal(),
        p_timeout
    );
    IF v_response IS NULL THEN
        RAISE null_response;
    END IF;

    -- parse response
    BEGIN
        v_envelope := XMLType(v_response);
    EXCEPTION
        WHEN OTHERS THEN
            v_sqlerrm := SQLERRM;
            RAISE xml_parse_error;
    END;

    -- check for a fault
    v_fault := v_envelope.extract(  
        '/soap:Envelope/soap:Body/soap:Fault', 
        'xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"'
    );
    IF v_fault IS NOT NULL THEN
        v_sqlerrm := v_fault.extract('.//faultstring/text()').getStringVal();
        RAISE soap_fault;
    END IF;

    -- the actual response is the child of the <soap:Body /> element
    RETURN v_envelope.extract(
        '/soap:Envelope/soap:Body/*[position() = 1]', 
        'xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"'
    );

END;

Note that I removed our exception handling block as it's not particularly relevant to the example.

With that, you can have any other procedure generate the XML necessary to call a service, pass it through invoke, and parse the return value.

We developed this solution on a 9i database so we haven't looked into UTL_DBWS yet. It works great, though.