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package org.apache.juneau.annotation; | |
import static java.lang.annotation.ElementType.*; | |
import static java.lang.annotation.RetentionPolicy.*; | |
import java.lang.annotation.*; | |
import org.apache.juneau.*; | |
/** | |
* Maps constructor arguments to property names on beans with read-only properties. | |
* | |
* <p> | |
* This annotation can be used in the case of beans with properties whose values can only be set by passing them in | |
* through a constructor on the class. | |
* <br>Since method parameter names are lost during compilation, this annotation essentially redefines them so that they | |
* are available at runtime. | |
* | |
* <p> | |
* This annotation can only be applied to constructors and can only be applied to one constructor per class. | |
* | |
* <p> | |
* When present, bean instantiation is delayed until the call to {@link BeanMap#getBean()}. | |
* Until then, bean property values are stored in a local cache until <c>getBean()</c> is called. | |
* Because of this additional caching step, parsing into read-only beans tends to be slower and use more memory than | |
* parsing into beans with writable properties. | |
* | |
* <p> | |
* Attempting to call {@link BeanMap#put(String,Object)} on a read-only property after calling {@link BeanMap#getBean()} | |
* will result in a {@link BeanRuntimeException} being thrown. | |
* Multiple calls to {@link BeanMap#getBean()} will return the same bean instance. | |
* | |
* <ul class='seealso'> | |
* <li class='link'>{@doc juneau-marshall.Transforms.BeanConstructorAnnotation} | |
* </ul> | |
*/ | |
@Documented | |
@Target(CONSTRUCTOR) | |
@Retention(RUNTIME) | |
@Inherited | |
public @interface BeanConstructor { | |
/** | |
* The names of the properties of the constructor arguments. | |
* <p> | |
* The {@link org.apache.juneau.annotation.BeanConstructor @BeanConstructor} annotation is used to | |
* map constructor arguments to property names on bean with read-only properties. | |
* <br>Since method parameter names are lost during compilation, this annotation essentially redefines | |
* them so that they are available at runtime. | |
* </p> | |
* <p> | |
* The definition of a read-only bean is a bean with properties with only getters, like shown below: | |
* </p> | |
* <p class='bpcode w800'> | |
* <jc>// Our read-only bean.</jc> | |
* <jk>public class</jk> Person { | |
* <jk>private final</jk> String <jf>name</jf>; | |
* <jk>private final int</jk> <jf>age</jf>; | |
* | |
* <ja>@BeanConstructor</ja>(properties=<js>"name,age"</js>) | |
* <jk>public</jk> Person(String name, <jk>int</jk> age) { | |
* <jk>this</jk>.<jf>name</jf> = name; | |
* <jk>this</jk>.<jf>age</jf> = age; | |
* } | |
* | |
* <jc>// Read only properties.</jc> | |
* <jc>// Getters, but no setters.</jc> | |
* | |
* <jk>public</jk> String getName() { | |
* <jk>return</jk> <jf>name</jf>; | |
* } | |
* | |
* <jk>public int</jk> getAge() { | |
* <jk>return</jk> <jf>age</jf>; | |
* } | |
* } | |
* </p> | |
* <p class='bpcode w800'> | |
* <jc>// Parsing into a read-only bean.</jc> | |
* String json = <js>"{name:'John Smith',age:45}"</js>; | |
* Person p = JsonParser.<jsf>DEFAULT</jsf>.parse(json); | |
* String name = p.getName(); <jc>// "John Smith"</jc> | |
* <jk>int</jk> age = p.getAge(); <jc>// 45</jc> | |
* </p> | |
* <p> | |
* Note that the {@link Name @Name} annotation can also be used to identify bean property names on constructor | |
* arguments. If neither this annotation or {@link Name @Name} is used, then we try to get the property names | |
* from the parameter names if they are available in the bytecode. | |
* </p> | |
*/ | |
String properties() default ""; | |
} |