Yes, that is correct, `@Component` is a Spring bean and a Singleton.

If the class belongs to the service layer you may want to annotate it with `@Service` instead

But have in mind that in order for these annotations to be detected, you need to place this line in `applicationContext.xml`:

    &lt;context:component-scan base-package=&quot;com.yourcompany&quot; /&gt;

About singletons - spring beans are all in singleton scope by default. The only thing you have to have in mind is that you should not store state in field variables (they should only hold dependencies). Thus your application will be thread-safe, and you won&#39;t require a new instance of a bean each time. In other words, your beans are stateless.

By default - Yes.

However, you can override this behavior using the `@Scope` annotation. For example: `@Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)`



Why I&#39;m getting this PHP error?

    Fatal error: Class &#39;PHPUnit_Framework_TestCase&#39; not found in ...

Why, Fatal error: Class &#39;PHPUnit_Framework_TestCase&#39; not found in ...?

AFAIK:

C++ provides three different types of polymorphism.

   * Virtual functions
   * Function name overloading
   * Operator overloading

In addition to the above three types of polymorphism, there exist other kinds of polymorphism:

   * run-time
   * compile-time
   * ad-hoc polymorphism
   * parametric polymorphism

I know that _runtime polymorphism_ can be achieved by _virtual functions_
and _static polymorphism_ can be achieved by _template functions_

But for the other two 

   * ad-hoc polymorphism
   * parametric polymorphism
the [website says][1],

**ad-hoc polymorphism:**

If the range of actual types that can be used is finite and the combinations must be individually specified prior to use, this is called ad-hoc polymorphism.

**parametric polymorphism:**

If all code is written without mention of any specific type and thus can be used transparently with any number of new types it is called parametric polymorphism. 

I can hardly understand them :(

can anyone explain them both if possible with an example?
I hope the answers to this questions would be helpful for many new passouts from their colleges.


  [1]: http://www.exforsys.com/tutorials/c-plus-plus/polymorphism-an-introduction.html

Polymorphism in C++

Being fairly new to Spring I have a question about annotating a class. When annotating a class with `@Component` does this mean this class will be a Spring Bean and by default a singleton?

When annotating a class with @Component, does this mean it is a Spring Bean and Singleton?

<p>Being fairly new to Spring I have a question about annotating a class. When annotating a class with <code>@Component</code> does this mean this class will be a Spring Bean and by default a singleton?</p>


I would like to have a bidirectional JSON to Java serialization

I&#39;m using **successfully** the Java to JSON to JQuery path... (`@ResponseBody`)
e.g. 

    @RequestMapping(value={&quot;/fooBar/{id}&quot;}, method=RequestMethod.GET)
    	 public @ResponseBody FooBar getFooBar(
                @PathVariable String id,
                HttpServletResponse response , ModelMap model) {
    		response.setContentType(&quot;application/json&quot;);
    ...
    }

and In JQuery I use 

    $.getJSON(&#39;fooBar/1&#39;, function(data) {
        //do something
    });

this works **well** (e.g. annotations work already, thanks to all the answerers)

However, how do I do the **reverse** path: have JSON be serialized to a Java Object back using RequestBody? 

no matter what I try, I can&#39;t get something like this to work:

    @RequestMapping(value={&quot;/fooBar/save&quot;}, method=RequestMethod.POST)
    public String saveFooBar(@RequestBody FooBar fooBar,
            HttpServletResponse response , ModelMap model) {

      //This method is never called. (it does when I remove the RequestBody...)
    }

I have Jackson configured correctly (it serializes on the way out) and I have MVC set as annotations driven of course

How do I make it work? is it possible at all? or is Spring / JSON / JQuery is oneway (out)? 


----------


**Update:**

I changed this Jackson setting

	&lt;bean id=&quot;jsonHttpMessageConverter&quot;
		class=&quot;org.springframework.http.converter.json.MappingJacksonHttpMessageConverter&quot; /&gt;

	&lt;!-- Bind the return value of the Rest service to the ResponseBody. --&gt;
	&lt;bean
		class=&quot;org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter&quot;&gt;
		&lt;property name=&quot;messageConverters&quot;&gt;
			&lt;util:list id=&quot;beanList&quot;&gt;
				&lt;ref bean=&quot;jsonHttpMessageConverter&quot; /&gt;
	&lt;!-- 			&lt;ref bean=&quot;xmlMessageConverter&quot; /&gt; --&gt;				
			&lt;/util:list&gt;
		&lt;/property&gt;
	&lt;/bean&gt;


To the (almost similiar one) suggested 

 

    &lt;bean id=&quot;jacksonMessageConverter&quot;
    	class=&quot;org.springframework.http.converter.json.MappingJacksonHttpMessageConverter&quot;&gt;&lt;/bean&gt;
    	&lt;bean
    		class=&quot;org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter&quot;&gt;
    		&lt;property name=&quot;messageConverters&quot;&gt;
    			&lt;list&gt;
    				&lt;ref bean=&quot;jacksonMessageConverter&quot; /&gt;
    			&lt;/list&gt;
    		&lt;/property&gt;
    	&lt;/bean&gt; 


And it seems to work! I don&#39;t know what exactly did the trick, but it works...

JQuery, Spring MVC @RequestBody and JSON - making it work together

What is the difference between these 2? I found few results on google nothing conclusive. 

Here is a follow up question: 

Say I create spring mvc web app annotate couple of classes with @Controller annotation and create something that will successfully transfer some information from front end -&gt; back end and vice versa and perhaps some database might be involved on the back end side. 

What would you call that? Rest web service or servlet or something else ?

Difference between servlet and web service

We are planning to write a web application from the scratch, it has been decided to go with the latest edition of Glassfish which complies with Java EE 6 standard, therefore we are analyzing if CDI can be used instead of Spring. 

Can we say that CDI could be a replacement for Spring?

Is CDI a good replacement of Spring?

This is part of my `job.xml`:

    &lt;job id=&quot;foo&quot; job-repository=&quot;job-repository&quot;&gt;
      &lt;step id=&quot;bar&quot;&gt;
        &lt;tasklet transaction-manager=&quot;transaction-manager&quot;&gt;
          &lt;chunk commit-interval=&quot;1&quot;
            reader=&quot;foo-reader&quot; writer=&quot;foo-writer&quot;
          /&gt;
        &lt;/tasklet&gt;
      &lt;/step&gt;
    &lt;/job&gt;

This is the item reader:

    import org.springframework.batch.item.ItemReader;
    import org.springframework.beans.factory.annotation.Value;
    import org.springframework.stereotype.Component;
    @Component(&quot;foo-reader&quot;)
    public final class MyReader implements ItemReader&lt;MyData&gt; {
      @Override
      public MyData read() throws Exception {
        //...
      }
      @Value(&quot;#{jobParameters[&#39;fileName&#39;]}&quot;)
      public void setFileName(final String name) {
        //...
      }
    }

This is what Spring Batch is saying in runtime:

    Field or property &#39;jobParameters&#39; cannot be found on object of 
    type &#39;org.springframework.beans.factory.config.BeanExpressionContext&#39;

What&#39;s wrong here? Where I can read more about these mechanisms in Spring 3.0?

How to get access to job parameters from ItemReader, in Spring Batch?

I&#39;m using Spring Security 3 and Spring MVC 3.05.

I would like to print username of currently logged in user,how can I fetch UserDetails in my Controller?

    @RequestMapping(value=&quot;/index.html&quot;, method=RequestMethod.GET)
    	public ModelAndView indexView(){
             UserDetails user = ?
                    mv.addObject(&quot;username&quot;, user.getUsername());
    		ModelAndView mv = new ModelAndView(&quot;index&quot;);
    		return mv;
    	}	



Get UserDetails object from Security Context in Spring MVC controller

What is the practical difference between `RetentionPolicy.CLASS` and `RetentionPolicy.RUNTIME`?

It looks like both are recorded into the bytecode and both may be accessed at the run-time anyway.

RetentionPolicy CLASS vs. RUNTIME

I met [lombok](http://projectlombok.org/) today.  
I&#39;m very anxious to know how it works.  
[A Java Geek Article](http://blog.frankel.ch/lombok-reduces-your-boilerplate-code) gives some clues but it&#39;s not perfectly clear to me:
     

&gt; Java 6 removes apt and make javac able
&gt; to manage annotations, streamlining
&gt; the  process to obtain a simpler
&gt; single step computing. This is the
&gt; path taken by Lombok.

Maybe with Java 6 the compile process will be:
javac -&gt; apt -&gt; lombok apt process -&gt; read class files and add set/get methods using [ASM][1]?  

Could you show me more details about the mechanism?


  [1]: http://asm.ow2.org/index.html

How does lombok work?

Although this question asked many times and I have already used all the suggestion but still I am getting this error.

The User.java is

    @Entity
	@Table(name = &quot;USER&quot;)
	public class User implements UserDetails, Serializable {
	
		private static final long serialVersionUID = 2L;
	
		@Id
		@Column(name = &quot;USER_ID&quot;)
		@GeneratedValue(strategy = GenerationType.IDENTITY)
		private long id;
		@Column(name = &quot;USERNAME&quot;)
		private String username;
		@Column(name = &quot;PASSWORD&quot;)
		private String password;
		@Column(name = &quot;NAME&quot;)
		private String name;
		@Column(name = &quot;EMAIL&quot;)
		private String email;
		@Column(name = &quot;LOCKED&quot;)
		private boolean locked;
		@OneToMany(cascade=CascadeType.ALL, fetch = FetchType.EAGER)
		@ElementCollection(targetClass=Role.class)
		@Column(name = &quot;ROLE_ID&quot;)
		private Set&lt;Role&gt; roles;
	
		@Override
		public GrantedAuthority[] getAuthorities() {
			List&lt;GrantedAuthorityImpl&gt; list = new ArrayList&lt;GrantedAuthorityImpl&gt;(0);
			for (Role role : roles) {
				list.add(new GrantedAuthorityImpl(role.getRole()));
			}
			return (GrantedAuthority[]) list.toArray(new GrantedAuthority[list.size()]);
		}
	
		@Override
		public boolean isAccountNonExpired() {
			return true;
		}
	
		@Override
		public boolean isAccountNonLocked() {
			return !isLocked();
		}
	
		@Override
		public boolean isCredentialsNonExpired() {
			return true;
		}
	
		@Override
		public boolean isEnabled() {
			return true;
		}
	
		public long getId() {
			return id;
		}
	
		public void setId(long id) {
			this.id = id;
		}
	
		public String getName() {
			return name;
		}
	
		public void setName(String name) {
			this.name = name;
		}
	
		public String getEmail() {
			return email;
		}
	
		public void setEmail(String email) {
			this.email = email;
		}
	
		public boolean isLocked() {
			return locked;
		}
	
		public void setLocked(boolean locked) {
			this.locked = locked;
		}
	
		@Override
		public String getUsername() {
			return username;
		}
	
		public void setUsername(String username) {
			this.username = username;
		}
	
		@Override
		public String getPassword() {
			return password;
		}
	
		public void setPassword(String password) {
			this.password = password;
		}
	
		public void setRoles(Set&lt;Role&gt; roles) {
			this.roles = roles;
		}
	
		public Set&lt;Role&gt; getRoles() {
			return roles;
		}
	}

And the Role.java is

    @Entity
	@Table(name=&quot;ROLE&quot;)
	public class Role implements Serializable {
	
		@Id
		@GeneratedValue(strategy = GenerationType.IDENTITY)
		@Column(name=&quot;ROLE_ID&quot;)
		private long id;
		@Column(name=&quot;USERNAME&quot;)
		private String username;
		@Column(name=&quot;ROLE&quot;)
		private String role;
	
		
		public long getId() {
			return id;
		}
	
		public void setId(long id) {
			this.id = id;
		}
	
		public String getUsername() {
			return username;
		}
	
		public void setUsername(String username) {
			this.username = username;
		}
	
		public String getRole() {
			return role;
		}
	
		public void setRole(String role) {
			this.role = role;
		}
	}

This is my first attempt in hibernate annotation with JPA. So any suggestions will be very helpful. 

For hibernate the pom.xml&#39;s dependencies are:

        &lt;dependency&gt;
			&lt;groupId&gt;org.hibernate&lt;/groupId&gt;
			&lt;artifactId&gt;hibernate&lt;/artifactId&gt;
			&lt;version&gt;3.5.4-Final&lt;/version&gt;
			&lt;type&gt;pom&lt;/type&gt;
			&lt;scope&gt;compile&lt;/scope&gt;
		&lt;/dependency&gt;
		&lt;dependency&gt;
			&lt;groupId&gt;org.hibernate&lt;/groupId&gt;
			&lt;artifactId&gt;hibernate-annotations&lt;/artifactId&gt;
			&lt;version&gt;3.5.4-Final&lt;/version&gt;
			&lt;type&gt;jar&lt;/type&gt;
			&lt;scope&gt;compile&lt;/scope&gt;
		&lt;/dependency&gt;
		
		&lt;dependency&gt;
			&lt;groupId&gt;org.hibernate&lt;/groupId&gt;
			&lt;artifactId&gt;hibernate-core&lt;/artifactId&gt;
			&lt;version&gt;3.5.4-Final&lt;/version&gt;
			&lt;type&gt;jar&lt;/type&gt;
			&lt;scope&gt;compile&lt;/scope&gt;
		&lt;/dependency&gt;
		&lt;dependency&gt;
			&lt;groupId&gt;org.hibernate&lt;/groupId&gt;
			&lt;artifactId&gt;hibernate-validator&lt;/artifactId&gt;
			&lt;version&gt;3.1.0.GA&lt;/version&gt;
			&lt;type&gt;jar&lt;/type&gt;
			&lt;scope&gt;compile&lt;/scope&gt;
		&lt;/dependency&gt;
		&lt;dependency&gt;
			&lt;groupId&gt;org.hibernate&lt;/groupId&gt;
			&lt;artifactId&gt;hibernate-entitymanager&lt;/artifactId&gt;
			&lt;version&gt;3.5.4-Final&lt;/version&gt;
			&lt;type&gt;jar&lt;/type&gt;
			&lt;scope&gt;compile&lt;/scope&gt;
		&lt;/dependency&gt;

I have no clue about the fault.

Thanks.

org.hibernate.MappingException: Could not determine type for: java.util.Set

I&#39;m using my uuid as following:

    @Id
	@GeneratedValue(generator = &quot;uuid&quot;)
	@GenericGenerator(name = &quot;uuid&quot;, strategy = &quot;uuid&quot;)
	@Column(name = &quot;uuid&quot;, unique = true)
	private String uuid;

but I&#39;m getting a smart Hibernate warning:

&gt; Using
&gt; org.hibernate.id.UUIDHexGenerator
&gt; which does not generate IETF RFC 4122
&gt; compliant UUID values; consider using
&gt; org.hibernate.id.UUIDGenerator instead

So I want to switch to `org.hibernate.id.UUIDGenerator`, now my question is how should I tell it to Hibernate&#39;s generator. I saw some guy used it as a &quot;hibernate-uuid&quot; - so this is what I&#39;ve tried, but with negative result:

    @Id
	@GeneratedValue(generator = &quot;hibernate-uuid&quot;)
	@GenericGenerator(name = &quot;hibernate-uuid&quot;, strategy = &quot;hibernate-uuid&quot;)
	@Column(name = &quot;uuid&quot;, unique = true)
	private String uuid;




Using Hibernate UUIDGenerator via annotations

I was wondering how I could implement the simple factory pattern with Spring 3 annotations.  I saw in the documentation that you can create beans that call the factory class and run a factory method.  I was wondering if this was possible using annotations only.

I have a controller that currently calls 

    MyService myService = myServiceFactory.getMyService(test);
    result = myService.checkStatus();

MyService is an interface with one method called checkStatus().

My factory class looks like this:

    @Component
    public class MyServiceFactory {
    
    	public static MyService getMyService(String service) {
    		MyService myService;
    		
    		service = service.toLowerCase();
    		
    		if (service.equals(&quot;one&quot;)) {
    			myService = new MyServiceOne();
    		} else if (service.equals(&quot;two&quot;)) {
    			myService = new MyServiceTwo();
    		} else if (service.equals(&quot;three&quot;)) {
    			myService = new MyServiceThree();
    		} else {
    			myService = new MyServiceDefault();
    		}
    		
    		return myService;
    	}
    }

MyServiceOne class looks like this :

	@Autowired
	private LocationService locationService;
	
	public boolean checkStatus() {
          //do stuff
	}

When I run this code the locationService variable is alwasy null.  I beleive this is because I am creating the objects myself inside the factory and autowiring is not taking place.  Is there a way to add annotations to make this work correctly?

Thanks


Content Type	Original Author	Original Content on Stackoverflow
Question	Marco	View Question on Stackoverflow
Solution 1 - Spring	Bozho	View Answer on Stackoverflow
Solution 2 - Spring	Lea Zus	View Answer on Stackoverflow

When annotating a class with @Component, does this mean it is a Spring Bean and Singleton?

Spring Problem Overview

Spring Solutions

Solution 1 - Spring

Solution 2 - Spring

Polymorphism in C++

Why, Fatal error: Class 'PHPUnit_Framework_TestCase' not found in ...?

Attributions