Restful Web Services （Note from the book by the same name)

In RESTful architectures, the method information goes into the HTTP method. In Re-

source-Oriented Architectures, the scoping information goes into the URI.

http://www.myservice.org/discussion/2008/12/10/{topic}

If the HTTP method doesn’t

match the method information, the service isn’t RESTful. If the scoping information

isn’t in the URI, the service isn’t resource-oriented.

RPC stands for Remote Procedure Call

An RPC-style web service accepts an envelope full of data from its client, and sends a

similar envelope back. such as SOAP

XML-RPC is mostly a legacy protocol these days,

Every RPC-style service defines a brand new vocabulary. By contrast, all RESTful web services share a standard vocabulary of

HTTP methods.

HTTP and more

HTTP:

connectionless and stationless

each request requires its own connection.

it has no memory of prior connections.

GET method. containing no body content, a GET request is comprised of only a method statement and various request header fields

GET /login.html HTTP/1.1

User-Agent ...

Even though a GET request does not send any information in the body of the message, data can still be pased as part of the GET statement itself

GET /login.html?username=dustin&...

GET method is normally used to request static data.

conditional GET: if a GET request includes and IF-Modified-Since

http servers tranditionally store GET parameters in system environment variables that can be accessed by CGI programs.

POST Method

is commonly used for passing user input to the server. all the info is stored in the body of the request rather than in the URL portion of the method statement.

advantages: info is not visible in the URL and there is no limit to the amount of information that can be passed.

POST /login.html http:/1.1

more header info

(in the body) username=dustin&...

basic authentication:

GET /salary.html HTTP/1.0

Authorization: Basic TATATATTTT (BASE64 encoding of the username and password)

MIME

Multipurpose Internet Mail Extensions

Web Basics

URI:Uniform Resource Identifer

is a term referring to any specification that identifies an object on the internet. there are two types URIs--URL(Uniform Resource Locator) and Uniform Resource Name.

URL is a specification for identifying an object, such as a file, newsgroup,CGI program by indicating its exact location on the internet.

URN is a method for referencing an object without declaring the full path to the object. rather by its location, a resource is referenced by its an alias. in case the resource is removed, all there are multiple copies on different servers in different parts of the world. when a request is made for a URN, the browser could locate the nearest copy of the resource and return it. URN is not supported by most software.

format

http://host[:port]/path/resource_name[#section][?query_string]

ftp://username:password@host[:port]/path

try{

url=new URL("http://yahoo.com/index.html")

}

catch(MalformedURLException e){

}

BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));

String nextLine = in.readLine

this return html files

absolute URL

relative URL

URL encoding:

URLs are comprised of a string of printable characters within ASCII coded character set. Any unsafe or nonprintable characters within a URL must be encoded. URL encoding involves replacing those characters with % followed by two hexadecimal digits corresponding to the character's ASCII value.

%20 is space, but it is so common, it is encoded as a single plus +

then + itself is encoded as %2B

Java includes a class to help convert resource names and other references into URL safe strings

URLEncoder.encode(string)

Web browser: is a client application that requests, receives, and displays HTML tags

web server is also called httpserver, responds to requests from a web browser by returning html,images ..also responsible for enforcing security polices, logging , cach

simple web server implementation

ServerSocket serverConnect ServerSocket(port); listen on port

HttpServer server = new HttpServer(serverConnect.accept())

CGI: common Gateway Interface

is a standard interface between an HTTP server and an application.CGI enables the Web server to generate dynamic content rather than just return static HTML files.In addition, because CGI can accept and process information submitted by the user,it can provide two way interaction between the client and the web server.

线程之间怎么通讯？什么是critical section/semaphore/mutax，区别？

线程之间怎么通讯？什么是critical section/semaphore/mutax，区别？
网上找到这么一段话,

how do 2 threads communicate?

Basically via memory i.e. member fields of a class. Any thread can write into a single field and let any other thread read its value.
But if you need to make sure that any value written into the field will also be found/read by another thread, you need to put the statements accessing your communication field into blocks

synchronized( lockObj ){ commField= ...; }

The lockObj is a central object (also called semaphore or mutex - for mutual exclusion ) you should choose carefully so that it can be accessed from all your classes and very early: think of an instance of java.lang.Class : that's a foolproof singleton.

I want to discourage you from using the "fast and easy" synchronized qualifier for methods. This way you end up with a mess of Locks and creating deadlocks!

what is critical section

In concurrent programming a critical section is a piece of code that accesses a shared resource (data structure or device) that must not be concurrently accessed by more than one thread of execution. A critical section will usually terminate in fixed time, and a thread, task or process will have to wait a fixed time to enter it (aka bounded waiting). Some synchronization mechanism is required at the entry and exit of the critical section to ensure exclusive use.

--

what is semaphore

In computer science, a semaphore is a variable or abstract data type that provides a simple but useful abstraction for controlling access by multiple processes to a common resource in a parallel programming environment.

--

A mutex is essentially the same thing as a binary semaphore, and sometimes uses the same basic implementation. However, the term "mutex" is used to describe a construct which prevents two processes from executing the same piece of code, or accessing the same data, at the same time. The term "binary semaphore" is used to describe a construct which limits access to a single resource.

In many cases a mutex has a concept of an "owner": the process which locked the mutex is the only process allowed to unlock it. In contrast, semaphores generally do not have this restriction, something the producer-consumer example above depends upon.

ejb migration

http://onjava.com/pub/a/onjava/2005/03/09/ejb-migration.html

heap vs stack

http://www.maxi-pedia.com/what+is+heap+and+stack

very good article about heap and stack

What is stack?

The two sections other from the code segment in the memory are used for data. The stack is the section of memory that is allocated for automatic variables within functions.

Data is stored in stack using the Last In First Out (LIFO) method. This means that storage in the memory is allocated and deallocated at only one end of the memory called the top of the stack. Stack is a section of memory and its associated registers that is used for temporary storage of information in which the most recently stored item is the first to be retrieved.

What is heap?

On the other hand, heap is an area of memory used for dynamic memory allocation. Blocks of memory are allocated and freed in this case in an arbitrary order. The pattern of allocation and size of blocks is not known until run time. Heap is usually being used by a program for many different purposes.

The stack is much faster than the heap but also smaller and

Semaphores in JDK 1.5

http://www.developerfusion.com/article/84294/semaphores-in-jdk-15/

very good article about threads and semaphore, easy to understand