Java getDeclaredFields of a class with missing dependencies

Question

I am having trouble getting the declared fields of an Object that is missing/not using specific dependencies.

Field[] fields = OBJECT.getClass().getDeclaredFields();

throws a NoClassDefFoundError when that object has imports to missing classes.

The reason I want to do this is for a Bukkit plugin. I want to get the fields of a plugin instance that has missing dependencies (they are not used, but the plugin can start).

At runtime that plugin will check if the required dependencies are present and depending on that it will load those specific fields.

Possible solutions I thought of:
1) Virtually create the missing classes + packages and try again using ASM. But I don't really know how to do this.

Regards,
Maxim

Assuming you are writing this plugin, why not just get rid of the redundant imports? — JamesB, Jul 09 '14 at 09:26
I am not writing the plugins I want to get the fields of, so I can't modify them. — Maximvdw, Jul 09 '14 at 09:29

score 0 · Answer 1 · answered Sep 13 '14 at 17:12

0

Why should you care the fields while missing dependencies?

If it happen, the class should never have an instance at runtime. I don't think JRE will allows to create instance of object with missing class for it's field.

It might mean something if you read getDeclaredMethods.

ASM / BCEL is a good direction to go, but not virtually create the missing classes (as you will not know who they are). You are use them to read/parse the "class file" to decode it signature (i.e. getDeclaredFields without using classloader).

answered Sep 13 '14 at 17:12

Dennis C

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I don't want to load/get them. The plugin I want to load has fields referring to references (private PluginB pluginb;) At runtime that plugin will load that dependency (If present). I get the noclassdeffound error when using "getDeclaredFields" – Maximvdw Sep 14 '14 at 10:44

score 0 · Answer 2 · edited Jan 15 '22 at 08:50

First of all make sure, that your target plugin is loaded before your plugin: You could force it to load, before your plugin, by adding this line to your plugin.yml file:

...
softdepend: [plugin_name1]
...

Where the plugin_name1 is your reflection target plugin.

Secondly, you should only get the fields, you need from this plugin, not listing every field, but if you would like to get it's all fields, than just decompile it's code and make a custom field getter method:

public ArrayList<Field> getFields(Class cl, String... analyze) {
    ArrayList<Field> fields = new ArrayList<Field>();

    for (String f : analyze) {
        try {
            Field field = cl.getDeclaredField(f);
            field.setAccessible(true);
            fields.add(field);
        } catch (Throwable err) {}
    }

    return fields;
}

Java getDeclaredFields of a class with missing dependencies

2 Answers2