This reference provides sample codes for the login() call.

Login login = new Login();
login.setUsername("username@company.com");
login.setPassword("password");
LoginResponse resp = stub.login(login);
LoginResult result = resp.getResult();
// set new endpoint
ServiceClient client = stub._getServiceClient();
client.getOptions().getTo().setAddress(result.getServerUrl());
// create session for all subsequent calls
SessionHeader header = new SessionHeader();
header.setSession(result.getSession());

<!-- sample login call -->
<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ns2="http://object.api.zuora.com/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:ns1="http://api.zuora.com/">
    <SOAP-ENV:Body>
        <ns1:login>
            <ns1:username>username@zuora.com</ns1:username>
            <ns1:password>password</ns1:password>
        </ns1:login>
    </SOAP-ENV:Body>
</SOAP-ENV:Envelope>

<!-- sample login response -->
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
    <soapenv:Body>
        <ns1:loginResponse xmlns:ns1="http://api.zuora.com/">
            <ns1:result>
                <ns1:Session>LiUBQF...ugxg2jJuCA==</ns1:Session>
                <ns1:ServerUrl>https://apisandbox.zuora.com/apps/services/a/26.0</ns1:ServerUrl>
            </ns1:result>
        </ns1:loginResponse>
    </soapenv:Body>
</soapenv:Envelope>

<!-- sample API query -->
<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ns2="http://object.api.zuora.com/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:ns1="http://api.zuora.com/">
    <SOAP-ENV:Header>
        <ns1:SessionHeader>
            <ns1:session>LiUBQF...ugxg2jJuCA==</ns1:session>
        </ns1:SessionHeader>
    </SOAP-ENV:Header>
    <SOAP-ENV:Body>
        <ns1:query>
            <ns1:queryString>select id from account</ns1:queryString>
        </ns1:query>
    </SOAP-ENV:Body>
</SOAP-ENV:Envelope>