ClassLoader

port	description
9001	glassfish with using WebAppClassLoader
9002	glassfish without using WebAppClassLoader
9003	tomcat, default

Explanation

1. java.lang.String is loaded by bootstrap class loader which is null here since it is the 'parent' of application class loader

2. javax.ws.rs-api is included in glassfish since it is a J2EE application server, and it comes with lots of J2EE implementation. So javax.ws.rs-api should be excluded from application war file, otherwise the version may differ from the one in the maven/gradle file.

   compileOnly group: 'javax.ws.rs', name: 'javax.ws.rs-api', version: '2.1'
   

3. By using WebAppClassLoader, glassfish will try to load third-party classes from application library first which is included in war file.

   For example, ObjectMapper is loaded from war file.

   However, ObjectMapper is loaded from glassfish itself if WebAppClassLoader is not used

4. By default, tomcat loads third-party classes from application library first

5. Tomcat is just a servlet container, so it doesn't have javax.ws.rs-api included.

Sample

run those commands:

(cd demo/ && ./demo.sh) && cat demo/result.log

result (file) is:

===============================================
curl -X GET localhost:9001/classloader-demo/demo
===============================================
[ {
  "className" : "java.lang.String",
  "doesExist" : true,
  "classLoaderName" : null,
  "jarUrl" : null
}, {
  "className" : "com.google.common.math.BigIntegerMath",
  "doesExist" : true,
  "classLoaderName" : "WebappClassLoader (delegate=false; repositories=WEB-INF/classes/)",
  "jarUrl" : "jar:file:/usr/glassfish4/glassfish/domains/domain1/applications/classloader-demo/WEB-INF/lib/guava-22.0.jar!/com/google/common/math/BigIntegerMath.class"
}, {
  "className" : "javax.ws.rs.core.Response",
  "doesExist" : true,
  "classLoaderName" : "javax.ws.rs-api [195]",
  "jarUrl" : "bundle://195.0:1/javax/ws/rs/core/Response.class"
}, {
  "className" : "com.fasterxml.jackson.databind.ObjectMapper",
  "doesExist" : true,
  "classLoaderName" : "WebappClassLoader (delegate=false; repositories=WEB-INF/classes/)",
  "jarUrl" : "jar:file:/usr/glassfish4/glassfish/domains/domain1/applications/classloader-demo/WEB-INF/lib/jackson-databind-2.8.8.jar!/com/fasterxml/jackson/databind/ObjectMapper.class"
} ]
===============================================
curl -X GET localhost:9002/classloader-demo/demo
===============================================
[ {
  "className" : "java.lang.String",
  "doesExist" : true,
  "classLoaderName" : null,
  "jarUrl" : null
}, {
  "className" : "com.google.common.math.BigIntegerMath",
  "doesExist" : true,
  "classLoaderName" : "com.google.guava [274]",
  "jarUrl" : "bundle://274.0:1/com/google/common/math/BigIntegerMath.class"
}, {
  "className" : "javax.ws.rs.core.Response",
  "doesExist" : true,
  "classLoaderName" : "javax.ws.rs-api [195]",
  "jarUrl" : "bundle://195.0:1/javax/ws/rs/core/Response.class"
}, {
  "className" : "com.fasterxml.jackson.databind.ObjectMapper",
  "doesExist" : true,
  "classLoaderName" : "com.fasterxml.jackson.core.jackson-databind [276]",
  "jarUrl" : "bundle://276.0:1/com/fasterxml/jackson/databind/ObjectMapper.class"
} ]
===============================================
curl -X GET localhost:9003/classloader-demo/demo
===============================================
[ {
  "className" : "java.lang.String",
  "doesExist" : true,
  "classLoaderName" : null,
  "jarUrl" : null
}, {
  "className" : "com.google.common.math.BigIntegerMath",
  "doesExist" : true,
  "classLoaderName" : "ParallelWebappClassLoader\r\n  context: classloader-demo\r\n  delegate: false\r\n----------> Parent Classloader:\r\njava.net.URLClassLoader@4eec7777\r\n",
  "jarUrl" : "jar:file:/usr/local/tomcat/webapps/classloader-demo/WEB-INF/lib/guava-22.0.jar!/com/google/common/math/BigIntegerMath.class"
}, {
  "className" : "javax.ws.rs.core.Response",
  "doesExist" : false,
  "classLoaderName" : null,
  "jarUrl" : null
}, {
  "className" : "com.fasterxml.jackson.databind.ObjectMapper",
  "doesExist" : true,
  "classLoaderName" : "ParallelWebappClassLoader\r\n  context: classloader-demo\r\n  delegate: false\r\n----------> Parent Classloader:\r\njava.net.URLClassLoader@4eec7777\r\n",
  "jarUrl" : "jar:file:/usr/local/tomcat/webapps/classloader-demo/WEB-INF/lib/jackson-databind-2.8.8.jar!/com/fasterxml/jackson/databind/ObjectMapper.class"
} ]