Why given code throws exception (Jsoup)

Question

As it is said on so many forums that element is a special case of node in DOM.

But I got an exception that violate this rule.

It throws exception at statement, elem.remove().

Here, ele is an element. remove() is a function in Jsoup API, that removes nodes and their descendants from DOM.

Exception :-

[WARNING] 
java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at org.codehaus.mojo.exec.ExecJavaMojo$1.run(ExecJavaMojo.java:297)
    at java.lang.Thread.run(Thread.java:722)
Caused by: java.lang.IllegalArgumentException: Object must not be null
    at org.jsoup.helper.Validate.notNull(Validate.java:16)
    at org.jsoup.nodes.Node.remove(Node.java:266)
    at XXX.YYY.ZZZ.Template_Matching.Template_Matching.removeProductLister(Template_Matching.java:80)
    at XXX.YYY.ZZZ.Template_Matching.Template_Matching.main(Template_Matching.java:376)
    ... 6 more
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE

Code :-

public static void function(Document doc1, Document doc2, String tag) {

        //Checking for ULs
        Elements uls_1 = doc1.getElementsByTag(tag);
        Elements uls_2 = doc2.getElementsByTag(tag);

        for (Element elem1 : uls_1) {

            // Check if elem1 exists in DOM, If No, then continue

            for (Element elem2 : uls_2) {

                // Check if elem2 exists in DOM, If No, then continue

                // If id matches, remove them
                if ((!"".equals(elem1.id())) && (elem1.id().equals(elem2.id()))) {
                    elem1.remove();
                    elem2.remove();
                    break;
                }
            }
        }
    }

You should make sure that doc1 and doc2 are different documents. — Alohci
– Alohci, Commented Apr 8, 2013 at 13:16
@Alohci Can I discuss on this. I will explain my code on chat? — devsda
– devsda, Commented Apr 8, 2013 at 13:23
Sorry, no. Your code looks to have problems, but since I don't know JSoup, I'm not sure which one(s) apply. I suggest you change the code so that you're not removing elements in the inner loop like that. Build a list of elements that you want to remove, then loop backwards once through the elements list for each dom to remove the elements. — Alohci
– Alohci, Commented Apr 8, 2013 at 13:56
@Alohci Ohk, I will do that. But when I remove elements from both lists, then I put break. It does the same, that you suggests. — devsda
– devsda, Commented Apr 8, 2013 at 14:22

Mugoma J. Okomba · Accepted Answer · 2016-05-31 12:45:05Z

3

The error happens when one tries to remove an element whose parent has already been removed. This could point to a bug in Jsoup. Doesn't removing a parent also remove the children?

A workaround is to first check if parent exists:

if (element != null && element.parent() != null) { // fixes java.lang.IllegalArgumentException in org.jsoup.helper.Validate.notNull
    element.remove();
}

answered May 31, 2016 at 12:45

Mugoma J. Okomba

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1 Comment

valepu Over a year ago

It might happen if you are iterating elements and delete the parent before its children so probably jsoup is behaving correctly but the error is modifying the elements in a loop

Bob Flannigon · Accepted Answer · 2013-04-08 12:46:14Z

2

Caused by: java.lang.IllegalArgumentException: Object must not be null

You need to check that you aren't accessing properties of null objects...

answered Apr 8, 2013 at 12:46

Bob Flannigon

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8 Comments

devsda Over a year ago

But this problem not arises regulary. Sometimes it arises, sometimes it runs fine.

Mesh Over a year ago

Surely elem1 and elem2 must not be null for the .id() accessor to not throw in the if(...)?

devsda Over a year ago

@Adrian Yes I checked this at the place where I commented // Check if elem1 exists in DOM, If No, then continue, If that element is not in DOM then continue, otherwise proceed.

Mesh Over a year ago

Is this something you can debug? Put a break point on elem1.remove(), and check the objects involved.... ( I'm no Java expert, and I cant discern what platform, environment you are running this code on)

devsda Over a year ago

@Adrian I am making my project on maven, coding in java. USing Jsoup library for making DOM.

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