Jetty Study Notes-jetty classloader

Document directory

• Classloader is mainly responsible for the work
• Classloader's find Class Method
• Classloader category
• Context classloader
• If childfirst is used, the search path is:

Java classloader Review

Take Sun JDK as an Example

Classloader is mainly responsible for the work

• Find class: Find the class
• Links class: class and File Link
• Define class: converts a binary file to an instance of the class.

Classloader's find Class Method

1. Findloadedclass: First, check whether it has been loaded by the current classloader.
2. Parent. loadclass: Call the parent loader to load data. If there is no parent loader, call the native findbootstrapclass * method to obtain the data.
3. Findclass: If none of the above is found, call the current findclass

Class c = findLoadedClass(name);                if (c == null) {                    try {                        if (parent != null) {                            c = parent.loadClass(name, false);                        } else {                            c = findBootstrapClass0(name);                        }                    } catch (ClassNotFoundException e) {                        // If still not found, then invoke findClass in order                        // to find the class.                        c = findClass(name);                    }                }

Classloader category

• Bootstraploader: Native. It is started after JVM is started. It is responsible for loading the core lib/class (including the following two classloader) in JRE ).
• Extclassloader: loaded by bootstraploader, responsible for loading the ext package in JRE, parent = NULL
• Appclassloader: loaded by bootstraploader, responsible for loading classes in classpath, parent = extclassloader
• Userclassloader: Custom classloader, specifying the resource location through URL

Context classloader

Implement the requirement for parent classloader to load the class in the sub-classloader URL
Jetty classloader

Webappclassloader. loadclass:

1. Find the existing class

Class<?> c= findLoadedClass(name);

2. If parentfirst or system_class is not server_class, parentfirst is used.

if (c == null && _parent!=null && (_context.isParentLoaderPriority() || system_class) && !server_class)        {            tried_parent= true;            try            {                c= _parent.loadClass(name);                if (Log.isDebugEnabled())                    Log.debug("loaded " + c);            }            catch (ClassNotFoundException e)            {                ex= e;            }        }

3. Otherwise, the current findclass is called.

 if (c == null)        {            try            {                c= this.findClass(name);            }            catch (ClassNotFoundException e)            {                ex= e;            }        }

4. Find the current Trojan and find the parent.

 if (c == null && _parent!=null && !tried_parent && !server_class )            c= _parent.loadClass(name);

5. Resolve

if (resolve)            resolveClass(c);

If childfirst is used, the search path is:

Webappclassloader --> bootstraploader --> extclassloader --> appclassloader