How to convert complex Xml to csv?

I am writing a program in java( pre-junior), I really need help with xslt transformation. It is necessary to make a csv file from xml.
I got this xslt filter:

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:output method="text" omit-xml-declaration="yes" indent="no"/>

    <xsl:template match="node()" name="conv">
        <xsl:call-template name="loop"/>
    </xsl:template>

    <xsl:template name="loop">

        <xsl:for-each select="./*[count(*) = 0]">
            <xsl:value-of select="."/>
            <xsl:if test="position() != last()">
                <xsl:text>,</xsl:text>
            </xsl:if>
            <xsl:if test="position() = last()">
                <xsl:text>,</xsl:text>
            </xsl:if>
        </xsl:for-each>
        <xsl:text>
</xsl:text>


        <xsl:for-each select="./*[(count(*) != 0) and (name()!='PARAMETRS')] ">
            <xsl:call-template name="loop"/>
        </xsl:for-each>
            <xsl:text>
</xsl:text>
    </xsl:template>
</xsl:stylesheet>

Source xml:

<Integration>
	<PARAMETRS>
		<ID>AZD</ID>
		<DATE>2020-01-01</DATE>
	</PARAMETRS>
	<ORG>
		<Thing>
			<object>10220</object>
			<type>U</type>
			<dyn>
				<items>
					<val>988009</val>
					<datebegin>2019-12-12</datebegin>
				</items>
			</dyn>
		</Thing>
		<Thing>
			<object>10221</object>
			<type>U</type>
			<dyn>
				<items>
					<val>988010</val>
					<datebegin>2019-12-13</datebegin>
				</items>
				<items>
					<val>988011</val>
					<datebegin>2019-12-14</datebegin>
				</items>
			</dyn>
		</Thing>
	</ORG>
</Integration>

In the output, I get comma-separated lines, and a few more lines (those same items) with the values below. and can't figure out how to concatenate the values ...
I would do it via value-of select = "concat" but my <items> may have several dyn (1, 2, 3 ...), hence this is not suitable.
The output needs a csv separated by commas.
Please advise how to concatenate the item with its parent? Or there are simpler ways to parse xml with a different number of subsections(childs).

Expected output:

10220,U,988009,2019-12-12
10221,U,988010,2019-12-13,988011,2019-12-14

The output you show can be easily obtained using the following stylesheet:

XSLT 1.0

<xsl:stylesheet version="1.0" 
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="text"/>

<xsl:template match="/Integration">
	<xsl:for-each select="ORG/Thing">
		<xsl:value-of select="object"/>
        <xsl:text>,</xsl:text>
		<xsl:value-of select="type"/>
        <xsl:text>,</xsl:text>
        <xsl:for-each select="dyn/items">
			<xsl:value-of select="val"/>
			<xsl:text>,</xsl:text>
			<xsl:value-of select="datebegin"/>
			<xsl:if test="position() != last()">
				<xsl:text>,</xsl:text>
			</xsl:if>
        </xsl:for-each>
        <xsl:text>
</xsl:text>
    </xsl:for-each>
</xsl:template>

</xsl:stylesheet>

Note that the output has a set of columns for each items; this is not an ideal CSV structure.

If you can use XSLT 2.0, it opens up new powerful functionality.

Oracle XML Developer Kit (XDK) supports XSLT 2.0

Here is the link: Using the XSLT Processor for Java

The approach below is doing the following:

• Using string-join() function to concatenate all child elements values
  on a different hierarchy level via .//*/(text()[1] expression.
• xs:token casting removes white spaces.
• XPath predicate [. != ''] removes empty sequence members.

XSLT 2.0

<?xml version='1.0'?>
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xs="http://www.w3.org/2001/XMLSchema">
	<xsl:output method="text"/>

	<xsl:template match="/Integration">
		<xsl:for-each select="ORG/Thing">
			<xsl:value-of select="string-join((.//*/(text()[1] cast as xs:token?))[. != ''],',')"/>
			<xsl:text>
</xsl:text>
		</xsl:for-each>
	</xsl:template>

</xsl:stylesheet>

> Output

10220,U,988009,2019-12-12
10221,U,988010,2019-12-13,988011,2019-12-14

Based on the Marting Honnen great tip, here is even more concise XSLT 2.0 version without any loop.

XSLT 2.0

<?xml version="1.0"?>
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xs="http://www.w3.org/2001/XMLSchema">
	<xsl:output method="text"/>

	<xsl:template match="/Integration">
		<xsl:value-of select="ORG/Thing/string-join((.//*/(text()[1] cast as xs:token?))[. != ''],',')" separator="
"/>
	</xsl:template>
</xsl:stylesheet>