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Some people asked:
> Why do you need custom classloading?
Short answer:
The code I=E2=80=99m trying to test will be loaded by custom ClassLoaders, =
and I=E2=80=99d rather unit test it with a setup as close to the run-time s=
etup as possible.
Longer answer:
I=E2=80=99ve created a =E2=80=9Cmodule framework=E2=80=9D (still looking fo=
r a good name; suggestions welcome) that mirrors the maven project hierarch=
y at runtime. Assume your maven projects look like this:
MAIN
MODULE_A
MODULE_C
MODULE_D
MODULE_E
MODULE_B
MODULE_C
MODULE_D
MODULE_E
to run my project, I say:
> java -jar mybootloader.jar -module MAIN
instead of having to create a really long class path that includes all the =
module jars. The module framework evaluates the pom file inside MAIN.jar, a=
nd recursively looks for the jars of submodules in a well-known place (e.g.=
~/.m2, or /usr/lib/java), and creates a ClassLoader for each one of them. =
(In the above example: 6 ClassLoaders) They delegate to each other in a str=
ucture that reflects the maven project hierarchy.
This has several advantages:
* isolation =E2=80=94 it=E2=80=99s much harder for code in one module with=
its own ClassLoader to =E2=80=9Cbreak out=E2=80=9D.=20
* I can dynamically add modules to a running program without much trouble,=
simply by adding another delegate ClassLoader to MODULE_C=E2=80=99s ClassL=
oader, for example. This is useful for dynamic plug-ins such as =E2=80=9Coh=
, this website I just came across references yet another media type=E2=80=
=9D)
* And I really hate distributing gigantic WARs and what have you that cont=
ain a ton of code that wasn=E2=80=99t actually updated: this lets me update=
just the one JAR at the time that was updated. This is a problem I=E2=80=
=99d like to solve nicely for UBOS http://ubos.net/ <http://ubos.net/> =E2=
=80=94 if it can be done for all languages, why not also for Java?
Because more things can go wrong with so many ClassLoaders than with only o=
ne, I=E2=80=99d like to have the same structure during junit testing.
The code for this currently resides at https://github.com/infogrid-org/info=
grid-modules <https://github.com/infogrid-org/infogrid-modules> but it will=
become a separate project, once I figure out a name for it! It works from =
the command line, and it works in Tomcat 8.
Does this make sense?
Cheers,
Johannes.
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=3Dutf-8"></head><body style=3D"word-wrap: break-word; -webkit-nbsp-mode: s=
pace; -webkit-line-break: after-white-space;" class=3D"">
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<br><br>
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<div>Some people asked:</div><div><br class=3D""></div><div><blockquote typ=
e=3D"cite" class=3D""><div class=3D""><div id=3D"ygrp-mlmsg" style=3D"font-=
size: 13px; font-family: Arial, helvetica, clean, sans-serif; font-style: n=
ormal; font-variant: normal; font-weight: normal; letter-spacing: normal; l=
ine-height: normal; orphans: auto; text-align: start; text-indent: 0px; tex=
t-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -w=
ebkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); positio=
n: relative;" class=3D""><div id=3D"ygrp-msg" style=3D"line-height: 1.22em;=
z-index: 1;" class=3D""><div id=3D"ygrp-text" style=3D"line-height: 1.22em=
; font-family: Georgia;" class=3D""><div dir=3D"ltr" style=3D"line-height: =
1.22em;" class=3D""><div style=3D"line-height: 1.22em;" class=3D"">Why do y=
ou need custom classloading?</div></div></div></div></div></div></blockquot=
e><br class=3D""></div><div>Short answer:</div><div><br class=3D""></div><d=
iv>The code I=E2=80=99m trying to test will be loaded by custom ClassLoader=
s, and I=E2=80=99d rather unit test it with a setup as close to the run-tim=
e setup as possible.</div><div><br class=3D""></div><div>Longer answer:</di=
v><div><br class=3D""></div>I=E2=80=99ve created a =E2=80=9Cmodule framewor=
k=E2=80=9D (still looking for a good name; suggestions welcome) that mirror=
s the maven project hierarchy at runtime. Assume your maven projects look l=
ike this:<div class=3D""><br class=3D""></div><div class=3D"">MAIN</div><di=
v class=3D""> MODULE_A</div><div class=3D""> &nbs=
p; MODULE_C</div><div class=3D""> =
MODULE_D</div><div class=3D""> MODULE_E</=
div><div class=3D""> MODULE_B</div><div class=3D""> &nbs=
p; MODULE_C</div><div class=3D""><div class=3D"">  =
; MODULE_D</div><div class=3D""> &=
nbsp; MODULE_E</div></div><div class=3D""><br class=3D""></div><div =
class=3D"">to run my project, I say:</div><div class=3D""><br class=3D""></=
div><div class=3D"">> java -jar mybootloader.jar -module MAIN</div><div =
class=3D""><br class=3D""></div><div class=3D"">instead of having to create=
a really long class path that includes all the module jars. The module fra=
mework evaluates the pom file inside MAIN.jar, and recursively looks for th=
e jars of submodules in a well-known place (e.g. ~/.m2, or /usr/lib/java), =
and creates a ClassLoader for each one of them. (In the above example: 6 Cl=
assLoaders) They delegate to each other in a structure that reflects the ma=
ven project hierarchy.</div><div class=3D""><br class=3D""></div><div class=
=3D"">This has several advantages:</div><div class=3D""> * isolation =
=E2=80=94 it=E2=80=99s much harder for code in one module with its own Clas=
sLoader to =E2=80=9Cbreak out=E2=80=9D. </div><div class=3D""> * =
I can dynamically add modules to a running program without much trouble, si=
mply by adding another delegate ClassLoader to MODULE_C=E2=80=99s ClassLoad=
er, for example. This is useful for dynamic plug-ins such as =E2=80=9Coh, t=
his website I just came across references yet another media type=E2=80=9D)<=
/div><div class=3D""> * And I really hate distributing gigantic WARs a=
nd what have you that contain a ton of code that wasn=E2=80=99t actually up=
dated: this lets me update just the one JAR at the time that was updated. T=
his is a problem I=E2=80=99d like to solve nicely for UBOS <a href=3D"http:=
//ubos.net/" class=3D"">http://ubos.net/</a> =E2=80=94 if it can be do=
ne for all languages, why not also for Java?</div><div class=3D""><br class=
=3D""></div><div class=3D"">Because more things can go wrong with so many C=
lassLoaders than with only one, I=E2=80=99d like to have the same structure=
during junit testing.</div><div class=3D""><br class=3D""></div><div class=
=3D"">The code for this currently resides at <a href=3D"https://github=
.com/infogrid-org/infogrid-modules" class=3D"">https://github.com/infogrid-=
org/infogrid-modules</a> but it will become a separate project, once I=
figure out a name for it! It works from the command line, and it works in =
Tomcat 8.</div><div class=3D""><br class=3D""></div><div class=3D""><div cl=
ass=3D"">Does this make sense?</div></div><div class=3D""><br class=3D""></=
div><div class=3D"">Cheers,</div><div class=3D""><br class=3D""></div><div =
class=3D""><br class=3D""></div><div class=3D""><br class=3D""></div><div c=
lass=3D"">Johannes.</div><div class=3D""><br class=3D""></div>
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<hr style=3D"height:2px ; border-width:0; color:#E3E3E3; backgroun=
d-color:#E3E3E3;">
Posted by: Johannes Ernst <[email protected]> =
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