How to understand java reflect
What this article shares with you is about how to understand java reflect. The editor thinks it is very practical, so I share it with you to learn. I hope you can get something after reading this article.
SelectedSelectionKeySet selectedKeySet = new SelectedSelectionKeySet ()
Class selectorImplClass =
Class.forName ("sun.nio.ch.SelectorImpl", false, ClassLoader.getSystemClassLoader ())
/ / Ensure the current selector implementation is what we can instrument.
If (! selectorImplClass.isAssignableFrom (selector.getClass () {
Return selector
}
Field selectedKeysField = selectorImplClass.getDeclaredField ("selectedKeys")
Field publicSelectedKeysField = selectorImplClass.getDeclaredField ("publicSelectedKeys")
SelectedKeysField.setAccessible (true)
PublicSelectedKeysField.setAccessible (true)
SelectedKeysField.set (selector, selectedKeySet)
PublicSelectedKeysField.set (selector, selectedKeySet)
SelectedKeys = selectedKeySet
Take a look at the first line, SelectedSelectionKeySet selectedKeySet = new SelectedSelectionKeySet (); what is this thing for? instead of the selectKeys field in the default implementation of selector, the implementation is very powerful. We'll see later.
Skip the unimportant part and go straight to this part.
Field selectedKeysField = selectorImplClass.getDeclaredField ("selectedKeys")
Field publicSelectedKeysField = selectorImplClass.getDeclaredField ("publicSelectedKeys")
Get 2 field in order to forget the value set in the object selector.
SelectedKeysField.setAccessible (true)
PublicSelectedKeysField.setAccessible (true)
SelectedKeysField.set (selector, selectedKeySet)
PublicSelectedKeysField.set (selector, selectedKeySet)
Then it is to set the value to access the attribute, and modify the two attributes of selector (selectedKeys and publicSelectedKeys), set the value to the selectedKeySet from the previous new, and then let selectedKeys = selectedKeySet. When selector executes select, it will modify the attribute value in selectedKeys.
Then take a look at what is really going on in SelectedSelectionKeySet:
Final class SelectedSelectionKeySet extends AbstractSet {
Private SelectionKey [] keysA
Private int keysASize
Private SelectionKey [] keysB
Private int keysBSize
Private boolean isA = true
SelectedSelectionKeySet () {
KeysA = new SelectionKey [1024]
KeysB = keysA.clone ()
}
@ Override
Public boolean add (SelectionKey o) {
If (o = = null) {
Return false
}
If (isA) {
Int size = keysASize
KeysA [size + +] = o
KeysASize = size
If (size = = keysA.length) {
DoubleCapacityA ()
}
} else {
Int size = keysBSize
KeysB [size + +] = o
KeysBSize = size
If (size = = keysB.length) {
DoubleCapacityB ()
}
}
Return true
}
Private void doubleCapacityA () {
SelectionKey [] newKeysA = new SelectionKey [keysA.length
