A Context is a collection of data, often stored in a `Map` or in a custom class which acts as a struct with accessors and modifiers.  It is used for maintaining state and for sharing information within a system. [See this PDF for an indepth description][1]. Though it can be used for efficient and effective data sharing, you should note that many are wary of the `Context` pattern as [an anti-pattern][2].


  [1]: https://www.dre.vanderbilt.edu/~schmidt/PDF/Context-Object-Pattern.pdf
  [2]: https://stackoverflow.com/questions/986865/can-you-explain-the-context-design-pattern-a-bit/986947#986947

An example for it might be the HttpSession object: you have attributes which is basically a map with String keys and Object elements. This provides state information between http requests. Another example is the ServletRequest which provides state information between Servlets.

See https://stackoverflow.com/questions/986865/can-you-explain-the-context-design-pattern-a-bit/16161219#16161219 for a thorough description of the pattern.

My post there also explains why it&#39;s not an anti-pattern - but the botched implementation of it is.

&quot;Context&quot; comes from &quot;Contextual Information&quot;.

From Msu.edu:

&gt; Contextual Information: Information that is in addition to the actual text of the document, such as date sent, sender’s identity, addressee’s identity, routing information, and return receipts.

In most frameworks (and thus the design pattern), a Context Object stores information about an incoming request and corroborating a response.


I have a one-to-one relationship but hibernatetool complains when generating the schema. Here&#39;s an example that shows the problem:

    @Entity
    public class Person {
        @Id
        public int id;
    
        @OneToOne
        public OtherInfo otherInfo;

        rest of attributes ...
    }

Person has a one-to-one relationship with OtherInfo:

    @Entity
    public class OtherInfo {
        @Id
        @OneToOne(mappedBy=&quot;otherInfo&quot;)
        public Person person;

        rest of attributes ...
    }

Person is owning side of OtherInfo. OtherInfo is the owned side so person uses `mappedBy` to specify the attribute name &quot;otherInfo&quot; in Person.

I get the following error when using hibernatetool to generate the database schema:

    org.hibernate.MappingException: Could not determine type for: Person, at table: OtherInfo, for columns: [org.hibernate.mapping.Column(person)]
            at org.hibernate.mapping.SimpleValue.getType(SimpleValue.java:292)
            at org.hibernate.mapping.SimpleValue.createIdentifierGenerator(SimpleValue.java:175)
            at org.hibernate.cfg.Configuration.iterateGenerators(Configuration.java:743)
            at org.hibernate.cfg.Configuration.generateDropSchemaScript(Configuration.java:854)
            at org.hibernate.tool.hbm2ddl.SchemaExport.&lt;init&gt;(SchemaExport.java:128)
            ...

Any idea why? Am I a doing something wrong or is this a Hibernate bug?



JPA Hibernate One-to-One relationship

I accidentally created a repository without the default folders in TortoiseSVN then did a checkout locally.  Realized hey, I forgot to create that repository with the defaults so I deleted the repository using VisualSVN Server and then recreated the same repository name which now has the default folders trunk, etc.

Problem is, my local folder has already been checked out.  How can I change it/repoint to the new repository URL?

Change repository on your folder with TortoiseSVN

what is context object design pattern?

<p>what is context object design pattern ?</p>


I have been experimenting with using UUIDs as database keys.  I want to take up the least amount of bytes as possible, while still keeping the UUID representation human readable.

I think that I have gotten it down to 22 bytes using base64 and removing some trailing &quot;==&quot; that seem to be unnecessary to store for my purposes.  Are there any flaws with this approach?  

Basically my test code does a bunch of conversions to get the UUID down to a 22 byte String, then converts it back into a UUID.

    import java.io.IOException;
    import java.util.UUID;
    
    public class UUIDTest {
    
    	public static void main(String[] args){
    		UUID uuid = UUID.randomUUID();
    		System.out.println(&quot;UUID String: &quot; + uuid.toString());
    		System.out.println(&quot;Number of Bytes: &quot; + uuid.toString().getBytes().length);
    		System.out.println();
    		
    		byte[] uuidArr = asByteArray(uuid);
    		System.out.print(&quot;UUID Byte Array: &quot;);
    		for(byte b: uuidArr){
    			System.out.print(b +&quot; &quot;);
    		}
    		System.out.println();
    		System.out.println(&quot;Number of Bytes: &quot; + uuidArr.length);
    		System.out.println();
    		
    		
    	    try {
    	        // Convert a byte array to base64 string
    	        String s = new sun.misc.BASE64Encoder().encode(uuidArr);
    	        System.out.println(&quot;UUID Base64 String: &quot; +s);
    	        System.out.println(&quot;Number of Bytes: &quot; + s.getBytes().length);
    	        System.out.println();
    	        
    	        
    	        String trimmed = s.split(&quot;=&quot;)[0];
    	        System.out.println(&quot;UUID Base64 String Trimmed: &quot; +trimmed);
    	        System.out.println(&quot;Number of Bytes: &quot; + trimmed.getBytes().length);
    	        System.out.println();
    	        
    	        // Convert base64 string to a byte array
    	        byte[] backArr = new sun.misc.BASE64Decoder().decodeBuffer(trimmed);
    			System.out.print(&quot;Back to UUID Byte Array: &quot;);
    			for(byte b: backArr){
    				System.out.print(b +&quot; &quot;);
    			}
    			System.out.println();
    			System.out.println(&quot;Number of Bytes: &quot; + backArr.length);
    			
    			byte[] fixedArr = new byte[16];
    			for(int i= 0; i&lt;16; i++){
    				fixedArr[i] = backArr[i];
    			}
    			System.out.println();
    			System.out.print(&quot;Fixed UUID Byte Array: &quot;);
    			for(byte b: fixedArr){
    				System.out.print(b +&quot; &quot;);
    			}
    			System.out.println();
    			System.out.println(&quot;Number of Bytes: &quot; + fixedArr.length);
    			
    			System.out.println();
    			UUID newUUID = toUUID(fixedArr);
    			System.out.println(&quot;UUID String: &quot; + newUUID.toString());
    			System.out.println(&quot;Number of Bytes: &quot; + newUUID.toString().getBytes().length);
    			System.out.println();
    			
    			System.out.println(&quot;Equal to Start UUID? &quot;+newUUID.equals(uuid));
    			if(!newUUID.equals(uuid)){
    				System.exit(0);
    			}
    			
    			
    	    } catch (IOException e) {
    	    }
    
    	}
    	
    	
    	public static byte[] asByteArray(UUID uuid) {
    
    		long msb = uuid.getMostSignificantBits();
    		long lsb = uuid.getLeastSignificantBits();
    		byte[] buffer = new byte[16];
    
    		for (int i = 0; i &lt; 8; i++) {
    			buffer[i] = (byte) (msb &gt;&gt;&gt; 8 * (7 - i));
    		}
    		for (int i = 8; i &lt; 16; i++) {
    			buffer[i] = (byte) (lsb &gt;&gt;&gt; 8 * (7 - i));
    		}
    
    		return buffer;
    
    	}
    	
    	public static UUID toUUID(byte[] byteArray) {
    
    		long msb = 0;
    		long lsb = 0;
    		for (int i = 0; i &lt; 8; i++)
    			msb = (msb &lt;&lt; 8) | (byteArray[i] &amp; 0xff);
    		for (int i = 8; i &lt; 16; i++)
    			lsb = (lsb &lt;&lt; 8) | (byteArray[i] &amp; 0xff);
    		UUID result = new UUID(msb, lsb);
    
    		return result;
    	}
    	
    }

output:

    UUID String: cdaed56d-8712-414d-b346-01905d0026fe
    Number of Bytes: 36
    
    UUID Byte Array: -51 -82 -43 109 -121 18 65 77 -77 70 1 -112 93 0 38 -2 
    Number of Bytes: 16
    
    UUID Base64 String: za7VbYcSQU2zRgGQXQAm/g==
    Number of Bytes: 24
    
    UUID Base64 String Trimmed: za7VbYcSQU2zRgGQXQAm/g
    Number of Bytes: 22
    
    Back to UUID Byte Array: -51 -82 -43 109 -121 18 65 77 -77 70 1 -112 93 0 38 -2 0 38 
    Number of Bytes: 18
    
    Fixed UUID Byte Array: -51 -82 -43 109 -121 18 65 77 -77 70 1 -112 93 0 38 -2 
    Number of Bytes: 16
    
    UUID String: cdaed56d-8712-414d-b346-01905d0026fe
    Number of Bytes: 36
    
    Equal to Start UUID? true



Storing UUID as base64 String

What variables do I have to set/pass as arguments to the JVM to get log4j to run properly? And by properly I mean not complain and print to the console.  Can I see a typical example?

Note: I need to avoid creating a log4j.properties file in the application.

log4j configuration via JVM argument(s)?

Is there a way to delete entire directories recursively in Java?

In the normal case it is possible to delete an empty directory.
However when it comes to deleting entire directories with contents, it is not that simple anymore.

How do you delete entire directories with contents in Java?

Delete directories recursively in Java

How are we able to sort a `HashMap&lt;key, ArrayList&gt;`?

I want to sort on the basis of a value in the `ArrayList`.

How to sort a HashMap in Java

Given a string:

    String exampleString = &quot;example&quot;;

How do I convert it to an `InputStream`?

How do I convert a String to an InputStream in Java?

One part of domain-driven design that there doesn&#39;t seem to be a lot of detail on, is how and why you should isolate your domain model from your interface. I&#39;m trying to convince my colleagues that this is a good practice, but I don&#39;t seem to be making much headway...

They use domain entities where ever they please in the presentation and interface layers. When I argue to them that they should be using display models or DTOs to insulate the Domain layer from the interface layer, they counter that they don&#39;t see the business value in doing something like that, because now you have a UI object to maintain as well as the original domain object.  


So I&#39;m looking for some concrete reasons I can use to back this up. Specifically:

1. Why should we not use domain objects in our presentation layer?    
(if the answer is the obvious one, &#39;decoupling&#39;, then please explain why this is important in this context)
2. Should we use additional objects or constructs to isolate our domain objects from the interface?

Why should I isolate my domain entities from my presentation layer?

Is there any way to create all instance properties dynamically? For example, I would like to be able to generate all attributes in the constructor and still be able to access them after the class is instantiated like this: `$object-&gt;property`. Note that I want to access the properties separately, and not using an array; here&#39;s an example of what I *don&#39;t* want:

    class Thing {
        public $properties;
        function __construct(array $props=array()) {
            $this-&gt;properties = $props;
        }
    }
    $foo = new Thing(array(&#39;bar&#39; =&gt; &#39;baz&#39;);
    # I don&#39;t want to have to do this:
    $foo-&gt;properties[&#39;bar&#39;];
    # I want to do this:
    //$foo-&gt;bar;

To be more specific, when I&#39;m dealing with classes that have a large number of properties, I would like to be able to select all columns in a database (which represent the properties) and create instance properties from them. Each column value should be stored in a separate instance property.


Can you create instance properties dynamically in PHP?

It is safe to say that the [EAV/CR][1] database model is bad.  That said, 

Question: **What database model, technique, or pattern should be used to deal with &quot;classes&quot; of attributes describing e-commerce products which can be changed at run time?**  

In a good E-commerce database, you will store classes of options (like TV resolution then have a resolution for each TV, but the next product may not be a TV and not have &quot;TV resolution&quot;).  How do you store them, search efficiently, and allow your users to setup product types with variable fields describing their products?  If the search engine finds that customers typically search for TVs based on console depth, you could add console depth to your fields, then add a single depth for each tv product type at run time.

There is a nice common feature among good e-commerce apps where they show a set of products, then have &quot;drill down&quot; side menus where you can see &quot;TV Resolution&quot; as a header, and the top five most common TV Resolutions for the found set.  You click one and it only shows TVs of that resolution, allowing you to further drill down by selecting other categories on the side menu.  These options would be the dynamic product attributes added at run time.

**Further discussion:**

So long story short, **are there any links out on the Internet or model descriptions that could &quot;academically&quot; fix the following setup?**  I thank Noel Kennedy for suggesting a category table, but the need may be greater than that.  I describe it a different way below, trying to highlight the significance.  I may need a viewpoint correction to solve the problem, or I may need to go deeper in to the EAV/CR.

Love the positive response to the EAV/CR model.  My fellow developers all say what Jeffrey Kemp touched on below: &quot;new entities must be modeled and designed by a professional&quot; (taken out of context, read his response below).  The problem is:

 - entities add and remove attributes weekly &lt;br /&gt; *(search keywords dictate future attributes)*
 - new entities arrive weekly &lt;br /&gt; *(products are assembled from parts)*
 - old entities go away weekly &lt;br /&gt; *(archived, less popular, seasonal)*

The customer wants to add attributes to the products for two reasons:

 - department / keyword search / comparison chart between like products
 - consumer product configuration before checkout

The attributes must have significance, not just a keyword search.  If they want to compare all cakes that have a &quot;whipped cream frosting&quot;, they can click cakes, click birthday theme, click whipped cream frosting, then check all cakes that are interesting knowing they all have whipped cream frosting.  This is not specific to cakes, just an example.

  [1]: http://en.wikipedia.org/wiki/Entity-attribute-value_model

Entity Attribute Value Database vs. strict Relational Model Ecommerce

What are the scenarios when one would use a Monostate pattern instead of singleton inorder to maintain a global object?

Edit:
I know what Singleton and Monostate patterns are. Have also implemented Singleton in quite a few scenarios. Just want to know the scenarios (case examples) where MonoState pattern needs to be implemented.

For eg. I need to maintain list of columns per screen in my windows forms app. I could use a Singleton Dictionary in this case. However, I am storing a List&lt;ScreenDetails&gt; in the static global var and I wanted to provide indexers (since I need to dynamically add new entry to the list if key is not present) where I could specify ScreenDetails.ScreenName as a key &amp; get the ScreenDetails.ColumnsTable. Since indexers can&#39;t operate on a static class I changed the pattern to Monostate. 

So I would like to know which other scenarios may compel a user to use Monostate instead of Singletons.

Monostate vs. Singleton

What is a wrapper class?   
How are such classes useful?

Content Type	Original Author	Original Content on Stackoverflow
Question	Isabel Jinson	View Question on Stackoverflow
Solution 1 - Java	akf	View Answer on Stackoverflow
Solution 2 - Java	Tamas Rev	View Answer on Stackoverflow
Solution 3 - Java	Glen Best	View Answer on Stackoverflow
Solution 4 - Java	8bitjunkie	View Answer on Stackoverflow

what is context object design pattern?

Java Problem Overview

Java Solutions

Solution 1 - Java

Solution 2 - Java

Solution 3 - Java

Solution 4 - Java

Change repository on your folder with TortoiseSVN

JPA Hibernate One-to-One relationship

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