do you know if there is anyway that I can populate a javabean but i don't want to use reflection.
For example I have this xml template to pouplate it
Sample XML File
<property name = "card" value = "cdd"/>
public class Customer {
private String card;
public void setCard(String card) {
this.card = card;
}
public String getCard() {
}
}
I want to call setCard on the Java bean but I don't want to use reflection
since I've used it before and it's quite slow,
Are there any alternatives? How does Hibernate do it for example?
Thanks
Carlo
The only faster way (i.e. faster than using reflection) to populate a JavaBean from XML is to either write or generate some binding code that calls the setters with values extracted from the XML (in this case, from the XML attributes).
Hand writing the binding code is the simplest approach ... provided you don't have much to write.
Code could be generated as source code and compiled.
Code could be generated using a bytecode generation technology such as BCEL or ASM.
There may some existing XML-to-JavaBean binding generator, though existing bindings may well use reflection rather than code generation.
However, it is not clear this is worth going to the bother of avoiding reflection. While reflection is relatively expensive, XML is probably significantly more expensive. I'd recommend doing some profiling before you decide to use a more complicated implementation approach.
I'm pretty sure Hibernate uses reflection APIs deep under the hood. Groovy also has some nice support for automatically generating and using bean getters/setters which also ultimately use reflection under the hood as well.
Now there is an option where you could hard code your parser to read the xml and call the appropriate setter given the name attribute, but you run into the problem of your parser becoming brittle (when your model changes if that makes sense).
If the Bean is your's you may implement an interface like this:
/** Tries to set the property named key with the value given and returns true for success or false otherwise. */
boolean set(String key, Object value);
Then simply cast to that interface and try to use that method to set the properties. It sure needs some work in the bean - but avoids reflection.
Related
Just another Java problem (I'm a noob, I know): is it possible to use dynamic property binding in a Custom Control with a dynamic property getter in a Java bean?
I'll explain. I use this feature extensively in my Custom Controls:
<xp:inputTextarea id="DF_TiersM">
<xp:this.value><![CDATA[#{compositeData.dataSource[compositeData.fieldName]}]]></xp:this.value>
This is used in a control where both datasource and the name of the field are passed as parameters. This works, so far so good.
Now, in some cases, the datasource is a managed bean. When the above lines are interpreted, apparently code is generated to get or set the value of ... something. But what exactly?
I get this error: Error getting property 'SomeField' from bean of type com.sjef.AnyRecord which I guess is correct for there is no public getSomeField() in my bean. All properties are defined dynamically in the bean.
So how can I make XPages read the properties? Is there a universal getter (and setter) that allows me to use the name of a property as a parameter instead of the inclusion in a fixed method name? If XPages doesn't find getSomeField(), will it try something else instead, e.g. just get(String name) or so?
As always: I really appreciate your help and answers!
The way the binding works depends on whether or not your Java object implements a supported interface. If it doesn't (if it's just some random Java object), then any properties are treated as "bean-style" names, so that, if you want to call ".getSomeField()", then the binding would be like "#{obj.someField}" (or "#{obj['someField']}", or so forth).
If you want it to fall back to a common method, that's a job for either the DataObject or Map interfaces - Map is larger to implement, but is more standard (and you could inherit from AbstractMap if applicable), while DataObject is basically an XPages-ism but one I'm a big fan of (for reference, document data sources are DataObjects). Be warned, though: if you implement one of those, EL will only bind to the get or getValue method and will ignore normal setters and getters. If you want to use those when present, you'll have to write reflection code to do that (I recommend using Apache BeanUtils).
I have a post describing this in more detail on my blog: https://frostillic.us/f.nsf/posts/expanding-your-use-of-el-%28part-1%29
I understand, in Java we have parameters validation solution. I believe JAX-RS has various annotations both for validation and data extraction. My question is, if I want to implement my own parameter validation class for a standalone Java application, how would I make sure that a method is executed only when its parameters have been validated? I am using Reflection to spot parameters with #LowerCaseCheck and then performing validation on it, but not sure where to place this validation code.
public void print(#LowerCaseCheck String lowerCaseString) {
....
}
You need to change the byte code of the method to perform the check (or call a method which performs the check) The simplest way to do this might be to use an Aspect orientated library like AspectJ.
Look at gag for an example of a library that does what you're looking for. It uses the asm bytecode manipulation library to insert validation checks at the start of annotated methods.
Cant'you use Bean Validation (JSR-303) to solve your problem ?
the #Pattern(regexp) annotation seems to do just what you need.
public void print(#Pattern(regexp = "^[a-z]*$") String lowerCaseString) {
....
}
I'm developing a Scala extension to an existing Java ORM (Ebean). The goal of this project is to add as much type safety as possible to the ORM.
Instead of
Ebean.find(Product.class).fetch("name", "unit").findList()
I would finally like to be able to write something like
(objects of entity[Product] with attributes name and unit) getIt
(note that this is just a very first DSL approach).
The ORM model is already defined as
#Entity
public class {
public String name;
public String unit;
}
In order to achieve type safety at compile time for the attributes in the query, I would need to access them on e.g. a dummy object like (new Product()).name.
I think this is the best way to ensure that only such model members are used that exists on that class, but, at runtime, I need a way to recognize that this variable was accessed. Otherwise I would just call that member name and wouldn't know about this in my query.
Does anybody know a way how to achieve this? Is there a possibility to trace when a variable is accessed and to give that information, at runtime, to any other object?
I already thought about hooking into getters and setters instead of using public members in the model classes, but this would either make the query or the model very ugly. Another problem is that any additional specific methods would have to be added manually for each model.
I would be happy if anyone could suggest possible solutions. Thanks!
If you are willing to define the fields of your model objects as something like the Record Fields, what Emil suggested could work, but if you're building your solution on top of a Java ORM using custom types might be an issue. If you need to track field access I think your best bet will be runtime bytecode instrumentation using a library like CGLib or Javassist. You can pass an instrumented "dummy" object into the body of your function, then track which field was accessed in a thread local. That's how it's done in Squeryl.
You could take a gander at how the Lift folks have implemented Mapper and Records. It allows for type safe queries using companion objects (as well as using raw sql). It does require inheriting traits into your model and the fields are specified as objects and not regular vals. Might be helpfull though. You can find the source for the persistance stuff here.
I work with a dynamic Dataset model, which (in short) takes in attributes and stores them in a Map like this...
Dataset dataset = new Dataset();
dataset.setAttribute("name", "value");
...for later recovery, like this...
String value = dataset.getAttribute("name");
...and that has worked wonderfully for my purposes. But now I'm in a place where I'd like to use a templating engine to dynamically generate HTML. In the template, it's not ideal for me to do a lot of ${dataset.getAttribute("name")}. It would be rather nice if I could create artificial methods whenever something was added to a Dataset. For instance, if I did this...
dataset.setAttribute("name", "value");
...I'd like to be able to retrieve it like this...
String name;
name = dataset.name;
//or
name = dataset.getName();
...but so far I haven't been able to pull it off. What approach might I take here? Is it even doable?
Edit:
I understand that Velocity offers Property Lookup Rules to try to resolve dataset.name to dataset.get("name"), and that's great, but I need to know how to achieve this in the case that Velocity isn't the target as well.
See http://velocity.apache.org/engine/releases/velocity-1.5/user-guide.html#propertylookuprules
If your method was named get(String attribute) rather than getAttribute(String attribute), you could use the same syntax as for regular properties. So, either refactor your class, or add an additional get method that does the same thing as getAttribute, or transform your object into a Map, which has a get method.
In the past I have generated POJOs dynamically with Objectweb's ASM. This has the benefit that the underlying fields are type safe and much more efficient (esp for privative values)
You can use Dynamic Spring proxies with AOP technology or CGLib proxies. AOP could be used to describe getters like this : execution(public * com.bla.YourClass.get*())")
From what I've seen, it's fairly common for template engines for Java to support both
getters/setters of the form getAttribute, and
implementation of the Map interface
Before you spend too much time looking for a more generic solution (assuming the above won't be supported like it is in Velocity), it's probably worth taking a look at the other engines to see if any of them don't support it. If all your possible targets do, then you're probably fine relying on it.
I'm a big fan of making sure you actually have a problem before you spend the time to solve it.
I'm developing a framework in java which relies on a number of XML files with large number of parameters.
When reading the parameters from the XML file, I have to have a large if-else statement to decide what the parameters is and then call appropriate methods.
Is this normal? to have a large if-else statement?
I am thinking that there is a simple and neater way of doing this, e.g. Java XML mapping or Java Reflections? is this the answer? if so, can you please provide examples of how this is done so I don't have to rely on a large if-else statement?
Thanks!
You want to first create an interface:
public interface XMLParameterHandler {
public handle_parameter (String XMLData);
}
Next you want to create a map:
private Map<string, XMLParameterHandler> handlers;
...and initialize it with one of the relevant Map implementations:
this.handlers = new HashMap<>();
You need to implement the interface on a number of classes, one for each parameter you intend to handle. This is a good use of inner classes. Insert each of these implemented handerls into the map:
handlers.put ("Param1", new XMLParam1HandlerImpl());
handlers.put ("Param2", new XMLParam2HandlerImpl());
Then you can call the handler from the xml processing loop:
handlers.get (paramValue).handle_parameter(XmlData);
There is JAXB (http://en.wikipedia.org/wiki/Java_Architecture_for_XML_Binding) for mapping java class to xml.
But you can't map methods with it: you only can map attributes to xml file values (deserialize parameters from xml).
i recommend to use Map, that have parameter as key and xml entry as value(not whole xml)
Reflection would be one approach. Perhaps combined with a custom annotation on the target method to indicate which parameter to pass to that method. This is an advanced technique, though.
A more standard technique would be to use a map, where the key is the attribute name, and the value is an instance of an implementation of some interface you define, like AttributeHandler. The implementations then contain the code for each attribute. This involves writing a lot of little classes, but you can do them as anonymous classes to save space and keep the code inline.
a large if-else statement to decide what the parameters is and then call appropriate methods
You could instead use the Strategy design pattern, with one Strategy object per parameter, and use a map from the parameter name to the Strategy object to use. I've found this approach useful for even a moderately complicated application of XML.
It sounds to me as if you want a data-driven rule-based approach to writing your application, rather like you get in XSLT. One way of achieving this is to write it in XSLT instead of Java - XSLT, after all, was specifically designed for processing XML, while Java wasn't. If you can't do that, you could study how XSLT does it using rules and actions, and emulate this design in your Java code.
N functions with M parameters can always be implemented with a single function with M + 1 parameters.
If you need a big if then else statement to decide which method to dispatch to, then you can just add a parameter to your method and call a single method.
You shouldn't need an if-then-else statement to bind the parameter values.
If there is complex logic dependent on the particular parameter values, you might use a table driven approach. You can map various combinations of paramemter values into equivalence classes, then variouos equivalence class combinations into a row in a table with a unique id, then have a switch statement based on that unique id.