tailieunhanh - Designing Enterprise Applicationswith the J2EETM Platform 2nd phần 3

Tham khảo tài liệu 'designing enterprise applicationswith the j2eetm platform 2nd phần 3', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | DESIGN ISSUES AND GUIDELINES FOR JAVA CLIENTS 67 password Send the HTTP request. Code Example Java Client Code for Sending a Binary Request Code Example illustrates how a Java servlet might listen for requests from the Java client public void doPost HttpServletRequest req HttpServletResponse resp throws IOException ServletException Interpret the request. DataInputStream in new DataInputStream int command application binary DataOutputStream out new DataOutputStream byte command switch command case LOGIN_USER String username String password Check username and password against user database. Code Example Java Servlet Code for Interpreting a Binary Request These examples also illustrate a substantial cost of HTTP-based messaging in general you have to write code for parsing and interpreting messages. Unfortunately writing such code especially for multiple programmable clients can be time-consuming and error-prone. Java technologies for XML alleviate some of the burdens experienced with binary messaging. These technologies which include the Java API for XML Processing JAXP automate the parsing and aid the construction of XML messages. 68 CHAPTER 3 THE CLIENT TIER Messaging toolkits based on Java technology help interpret messages once they are parsed these toolkits implement open standards such as the Simple Object Access Protocol SOAP . The ability to parse and interpret messages automatically reduces development time and helps maintenance and testing. A side benefit of using XML messages is that alternate clients are easier to support as XML is a widely-accepted open standard. For example StarOffice Calc and Macromedia Flash clients could both read order data formatted in XML from the same JSP page and present the data in their respective interfaces. Also you can use XML to encode messages from a variety of clients. A C client for example could