With tomcat, if you want to change the root application you can either rename the directory ROOT or ROOT##myapp.  ROOT#myapp makes a lot of sense because it reminds you what's there.  However, that naming convention seems to conflict with ABCL.  My app under ROOT works fine, but when I name it to ROOT##myapp ABCL gives:

org.armedbear.lisp.IntegrityError
at org.armedbear.lisp.Primitives$pf_error.execute(Primitives.java:1577)
at org.armedbear.lisp.Primitive.execute(Primitive.java:113)
at org.armedbear.lisp.Symbol.execute(Symbol.java:803)
at org.armedbear.lisp.Lisp.error(Lisp.java:383)
at org.armedbear.lisp.ZipCache.get(ZipCache.java:222)
at org.armedbear.lisp.ZipCache.get(ZipCache.java:102)
at org.armedbear.lisp.Pathname.truename(Pathname.java:2275)
at org.armedbear.lisp.Load.findLoadableFile(Load.java:69)
at org.armedbear.lisp.Load.loadSystemFile(Load.java:305)
at org.armedbear.lisp.Interpreter.initializeLisp(Interpreter.java:172)
at org.armedbear.lisp.Interpreter.createInstance(Interpreter.java:72)
at com.arahant.lisp.ABCL.init(ABCL.java:35)
at com.arahant.utils.StartupListener.contextInitialized(StartupListener.java:225)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4792)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5256)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:754)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:730)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:734)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1140)
at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1875)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
ERROR placeholder called with arguments:
Failed to get cached ZipFile because java.io.FileNotFoundException: /home/arahant/apache-tomcat-8.5.31/demo/ROOT (No such file or directory)
Failed to get cached ZipFile because java.io.FileNotFoundException: /home/arahant/apache-tomcat-8.5.31/demo/ROOT (No such file or directory)
[ERROR] [utils.StartupListener    ] - 2018-05-30 12:42:02 Error initializing Lisp.
org.armedbear.lisp.IntegrityError
at org.armedbear.lisp.Primitives$pf_error.execute(Primitives.java:1577)
at org.armedbear.lisp.Primitive.execute(Primitive.java:113)
at org.armedbear.lisp.Symbol.execute(Symbol.java:803)
at org.armedbear.lisp.Lisp.error(Lisp.java:383)
at org.armedbear.lisp.ZipCache.get(ZipCache.java:222)
at org.armedbear.lisp.ZipCache.get(ZipCache.java:102)
at org.armedbear.lisp.Pathname.truename(Pathname.java:2275)
at org.armedbear.lisp.Load.findLoadableFile(Load.java:69)
at org.armedbear.lisp.Load.loadSystemFile(Load.java:305)
at org.armedbear.lisp.Interpreter.initializeLisp(Interpreter.java:172)
at org.armedbear.lisp.Interpreter.createInstance(Interpreter.java:72)
at com.arahant.lisp.ABCL.init(ABCL.java:35)
at com.arahant.utils.StartupListener.contextInitialized(StartupListener.java:225)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4792)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5256)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:754)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:730)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:734)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1140)
at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1875)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
org.armedbear.lisp.IntegrityError
at org.armedbear.lisp.Primitives$pf_error.execute(Primitives.java:1577)
at org.armedbear.lisp.Primitive.execute(Primitive.java:113)
at org.armedbear.lisp.Symbol.execute(Symbol.java:803)
at org.armedbear.lisp.Lisp.error(Lisp.java:383)
at org.armedbear.lisp.ZipCache.get(ZipCache.java:222)
at org.armedbear.lisp.ZipCache.get(ZipCache.java:102)
at org.armedbear.lisp.Pathname.truename(Pathname.java:2275)
at org.armedbear.lisp.Load.findLoadableFile(Load.java:69)
at org.armedbear.lisp.Load.loadSystemFile(Load.java:305)
at org.armedbear.lisp.Interpreter.initializeLisp(Interpreter.java:172)
at org.armedbear.lisp.Interpreter.createInstance(Interpreter.java:72)
at com.arahant.lisp.ABCL.init(ABCL.java:35)
at com.arahant.utils.StartupListener.contextInitialized(StartupListener.java:225)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4792)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5256)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:754)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:730)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:734)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1140)
at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1875)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
[ERROR] [utils.StartupListener    ] - org.armedbear.lisp.IntegrityError
at org.armedbear.lisp.Primitives$pf_error.execute(Primitives.java:1577)
at org.armedbear.lisp.Primitive.execute(Primitive.java:113)
at org.armedbear.lisp.Symbol.execute(Symbol.java:803)
at org.armedbear.lisp.Lisp.error(Lisp.java:383)
at org.armedbear.lisp.ZipCache.get(ZipCache.java:222)
at org.armedbear.lisp.ZipCache.get(ZipCache.java:102)
at org.armedbear.lisp.Pathname.truename(Pathname.java:2275)
at org.armedbear.lisp.Load.findLoadableFile(Load.java:69)
at org.armedbear.lisp.Load.loadSystemFile(Load.java:305)
at org.armedbear.lisp.Interpreter.initializeLisp(Interpreter.java:172)
at org.armedbear.lisp.Interpreter.createInstance(Interpreter.java:72)
at com.arahant.lisp.ABCL.init(ABCL.java:35)
at com.arahant.utils.StartupListener.contextInitialized(StartupListener.java:225)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4792)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5256)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:754)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:730)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:734)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1140)
at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1875)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)