MVEL

Null nested properties aren't being created

Details

  • Type: Bug Bug
  • Status: Closed Closed
  • Priority: Major Major
  • Resolution: Duplicate
  • Affects Version/s: 2.0.17
  • Fix Version/s: None
  • Component/s: Core
  • Labels:
    None
  • Number of attachments :
    0

Description

Using MVEL to set nested properties appears to be broken if the properties are null. Here's an example:

public static class User {
private Address address;

public Address getAddress()

{ return address; }

public void setAddress(Address address)

{ this.address = address; }

}

public static class Address {
private String city;

public String getCity()

{ return city; }

public void setCity(String city)

{ this.city = city; }

}

User u = new User();
Serializable expr = MVEL.compileSetExpression("address.city");
MVEL.executeSetExpression(expr, u, "Denver");

I thought that this was working in previous releases, but this now throws exceptions about null contexts and such.

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Brian Pontarelli added a comment -

Here's a stack trace:

java.lang.NullPointerException
at org.mvel2.optimizers.impl.refl.ReflectiveAccessorOptimizer.optimizeSetAccessor(ReflectiveAccessorOptimizer.java:261)
at org.mvel2.optimizers.dynamic.DynamicOptimizer.optimizeSetAccessor(DynamicOptimizer.java:72)
at org.mvel2.compiler.CompiledAccExpression.setValue(CompiledAccExpression.java:42)
at org.mvel2.MVEL.executeSetExpression(MVEL.java:964)

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Brian Pontarelli added a comment - Here's a stack trace: java.lang.NullPointerException at org.mvel2.optimizers.impl.refl.ReflectiveAccessorOptimizer.optimizeSetAccessor(ReflectiveAccessorOptimizer.java:261) at org.mvel2.optimizers.dynamic.DynamicOptimizer.optimizeSetAccessor(DynamicOptimizer.java:72) at org.mvel2.compiler.CompiledAccExpression.setValue(CompiledAccExpression.java:42) at org.mvel2.MVEL.executeSetExpression(MVEL.java:964)
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Mike Brock added a comment -

What are you expecting MVEL to do in these cases? Inject a new instance of Address automatically? If so, I can say that MVEL has never done anything like that.

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Mike Brock added a comment - What are you expecting MVEL to do in these cases? Inject a new instance of Address automatically? If so, I can say that MVEL has never done anything like that.
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Brian Pontarelli added a comment -

Yeah. That's what I was thinking. I guess I had never tried to use MVEL in the same way that JCatapult is doing property setting. JCatapult inspects the type of the property/field and creates a new instance if possible. This allows it to be used for form submits where the action isn't constructing large and complex object graphs manually. Looks like this:

MyACtion.java
public class MyAction {
  public User user;
}

Then in the form you can have something like:

form.html
<input type="text" name="user.address.city"/>

JCatapult will construct the object graph for you. I think that Struts and OGNL also do this, but it has been a while since I've been in there.

At the very least, a better error and exception would be nice.

Thanks for looking into it Mike.

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Brian Pontarelli added a comment - Yeah. That's what I was thinking. I guess I had never tried to use MVEL in the same way that JCatapult is doing property setting. JCatapult inspects the type of the property/field and creates a new instance if possible. This allows it to be used for form submits where the action isn't constructing large and complex object graphs manually. Looks like this: MyACtion.java public class MyAction { public User user; } Then in the form you can have something like: form.html <input type= "text" name= "user.address.city" /> JCatapult will construct the object graph for you. I think that Struts and OGNL also do this, but it has been a while since I've been in there. At the very least, a better error and exception would be nice. Thanks for looking into it Mike.
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Brian Pontarelli added a comment -

I've been thinking about this more. I'm wondering how MVCs and other frameworks are using MVEL for handling setting of JavaBean properties. I dug into Struts some more, which I haven't been in the code for years (although I'm a project member) and they are using OGNL with a NullHandler that instantiates the necessary classes.

The tool I built in JCatapult does it more simply with a boolean flag passed to the set method like this:

Bar.java
expressionEvaluator.setProperty("user.address.city", "Denver", true); // Instantiate

I know that one of the Struts developers had done some work with MVEL and the ValueStack, but I don't know how they overcame this obstacle. It seems that this is a good feature to add in some fashion.

Show
Brian Pontarelli added a comment - I've been thinking about this more. I'm wondering how MVCs and other frameworks are using MVEL for handling setting of JavaBean properties. I dug into Struts some more, which I haven't been in the code for years (although I'm a project member) and they are using OGNL with a NullHandler that instantiates the necessary classes. The tool I built in JCatapult does it more simply with a boolean flag passed to the set method like this: Bar.java expressionEvaluator.setProperty( "user.address.city" , "Denver" , true ); // Instantiate I know that one of the Struts developers had done some work with MVEL and the ValueStack, but I don't know how they overcame this obstacle. It seems that this is a good feature to add in some fashion.
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Mike Brock added a comment -

This is actually a duplicate JIRA, for an already closed issue. Although, I can't figure out where it is.

Basically, MVEL does not currently supporting instantiating objects in a null path automatically. This is a feature which is currently under consideration for MVEL 3.0.

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Mike Brock added a comment - This is actually a duplicate JIRA, for an already closed issue. Although, I can't figure out where it is. Basically, MVEL does not currently supporting instantiating objects in a null path automatically. This is a feature which is currently under consideration for MVEL 3.0.

People

  • Assignee:
    Mike Brock
    Reporter:
    Brian Pontarelli
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    Updated:
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