Take a Trip into the Forest: A Java Primer on Maps, Trees, and Collections

Sep. 8, 2016

This webinar is brought to you as part of the free monthly webinar series from:

Howard Greenberg@TLCC

Paul Della-Nebbia@PaulDN

Courtney Carter@Teamstudio

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Take a Trip Into the Forest - A Java Primer on Maps, Trees, and Collections

Your Presenter Today – Howard Greenberg

• Certified Lotus Instructor since R3

• Co-founded TLCC in 1997

• IBM Champion

• Prior to that 12 years at IBM in the PC group

• Also…

– Certified Public Accountant

– Certified Information Systems Auditor (CISA)

– Certified Flight Instructor

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Agenda

• Why Use Java Objects in Xpages?

• Introduction to Managed Beans

• Scoped Variables in SSJS

• Introduction to Maps

• The DataObject Implementation

• A Reporting Example

• Questions???

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Why Use Java in XPages?

• Performance (see my recorded webinar)

• Reporting

– Easily combine data from different sources

• Portability

– Back end

– Front end

• Code Maintenance

• Lots of code/knowledge out there

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Review - Managed Beans

• The XPages runtime manages the creation of your “managed bean”

– Request, View, Session, or Application scope• Refer to methods on your XPages or from other Java

code• How to:

– Create an entry in the Faces-Config file– Create your Java code

• Getters and Setters• No argument constructor

• Don’t have to use Managed Beans!

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SampleBean.javaSampleBeanDemo.xsp

Scoped Variables in SSJS

• sessionScope.testName

– read/write to a variable that is session scope

• Can store anything (string, Boolean, date, array, etc)

– Just don’t store Domino objects

• Why do we care???

– Scoped variables are stored as HashMaps

– Another way to access is:

• sessionScope.get(“testName”)

• sessionScope.put(“testName” , “A value”)

• Same as a Java Hash Map

– Let’s Learn more about these HashMaps!

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Some Java Terms - Collections, Interfaces and implementations

• Collections is a Framework/root interface

– Architecture for representing collections

• Has Interfaces, Implementations, Algorithms

• Interfaces

– Abstract Data Type

– Defines a base used by all the classes that implement • An interface in Java is similar to a class, but the body of

an interface can include only abstract methods and final fields (constants). A class implements an interface by providing code for each method declared by the interface.

• Implementations

– A class that uses an interface (we use this!)

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Collections Interface

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Map Interface

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Java HashMap Documentation

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Java documentation on HashMap

Some Different Collection Implementations

• Set, SortedSet

– No duplicate elements• HashSet, TreeSet, LinkedHashSet

• List

– Allows duplicates

– Ordered• ArrayList, LinkedList

• Map, SortedMap

– Key/Value pairs• HashMap, LinkedHashMap, TreeMap

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Which one do I use?

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Use Case: Configuration Data

• Goal

– Store configuration information

– Managed Bean with Application Scope

• Best choice is a HashMap

– Why? Back to the previous chart!

– Access values with a key

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Working with Maps

• Creationprivate HashMap<String,String> configData = new HashMap<String, String>();

• Set a valueconfigData.put(key ,value);

• Get a value (and test to see if key is there)public String getConfig(String key) {

String rtnString = "";

if (this.configData.containsKey(key)){

rtnString = this.configData.get(key);

}

return rtnString;

}

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Steps

1. Notes view/form to hold configuration data

2. Create new Java Class

3. Add Managed Bean to faces-config

– Set scope as needed

4. Implement Serializable in the Java class

5. Create “private” variable for HashMap

6. Create constructor to initialize data

– Walk the view to load up the keys/values

7. Generate Getter/Setter

8. Use on XPage or in other Java code

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ConfigBean.javaConfigBeanDemo.xsp

More on HashMaps - Iterate through Map

• Get all the keys as a Set– statesHashMap.keySet()

• Get all the values as a Set– statesHashMap.values()

• Get the key and value as a Set– statesHashMap.entrySet()

• Get the key with getKey() and the value with getValue()

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for (Entry<String, String> state :statesHashMap.entrySet()){myString = state.getValue() + "|" + state.getKey() ;debugMsg(myString);

}

LinkedHashMap

• A HashMap does not keep the insertion order (random)

• Need to keeps insertion order? LinkedHashMap

• Good when loading data from a Notes view (that is ordered already)

– Keeps same (insertion) order

• Otherwise basically the same as HashMap

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ArrayLists

• A list of objects (like an Array)

– Hold any data type/object

– Can search the values

– Can access an element in a certain position

• Perfect for feeding to:

– Values in a combo box, list box, etc.

– Repeats

– Data Tables

• To add at end:

– rtnList.add(stateLine);

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Use Case: Return values to a Combo Box

• Stop doing @DbColumns

– Slow!

• Load values from a view, store in memory

– FAST!

• Use Expression Language

– configBean.statesHashMap

• Use same ConfigBean as before (application scope)

– Method in Java is getStatesHashMap()

– Returns a List

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ConfigBean.javaConfigBeanDemo.xsp

Time Out for a Message!

• Do you Recycle?– View looping– NotesDateTime?– columnValues with a Date creates NotesDateTime objects

• Instead use the Domino API– Simpler code patterns– Never have to worry about recycle– Try/Catch block not required– Support for logging– Lots of cool new stuff

• Available on OpenNTF – Link to version 3– Get help via Slack/Stack Overflow

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Code Comparison – The Old Way

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private void initBean(Database curDb, String viewName) {try {View setupVw = curDb.getView(viewName);String key = "";String value = "";ViewEntry tempEntry;if (setupVw != null) {

ViewEntryCollection vwEntryCol = setupVw.getAllEntries();ViewEntry entryDoc = vwEntryCol.getFirstEntry();while (entryDoc != null){

Vector<?> colValues = entryDoc.getColumnValues();key = (String) colValues.elementAt(0);value = (String) colValues.elementAt(1);this.configData.put(key , value);tempEntry = vwEntryCol.getNextEntry(entryDoc);entryDoc.recycle();entryDoc = tempEntry;

}}

} catch (Exception e) {e.printStackTrace();

}}

Code Comparison – The Domino API Way

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private void initBean(Database curDb, String viewName) {View setupVw = curDb.getView(viewName);String key = "";String value = "";if (setupVw != null) {

for (ViewEntry entryDoc : setupVw.getAllEntries()){Vector<?> colValues = entryDoc.getColumnValues();

key = (String) colValues.elementAt(0);value = (String) colValues.elementAt(1);this.configData.put(key , value);

}}

} No Recycle!Uses a for loopNo Try/Catch block

ConfigBean2.javaDomAPIDemo.xsp

Ordered Lists

• Use Case

– Get a list of values always sorted by the value

• “Natural” sort order

– No duplicates

• TreeSet!

• Good for looping through a view, getting a value from a column

– Add to TreeSet and then you always have a sorted, unique list

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TreeSetBean.javaTreeSetBeanDemo.xsp

Custom Sorting of a TreeSet

• Suppose you don’t want the “natural” order???

– Use a custom sort when defining the TreeSet

– Comparator function

– Will always sort using this new sort definition

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public List<String> getArizonaTownsReversed() {TreeSet<String> sorted = new TreeSet<String>(new Comparator<String>() {

public int compare(String o1, String o2) {return o2.compareTo(o1);

}});

sorted.addAll(ArizonaTowns);return new ArrayList<String>(sorted);

}

TreeSetBean.javaTreeSetBeanDemo.xsp

Add all the towns in all the states in one object?

• Use a TreeMap

– Key,Value pair

• In this case, a state is the key, a list of towns (TreeSet) is the value

– Sorted on the Key value, natural order

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DataObject

• Way to implement an interface that works well with the Expression Language

– Any data type

– Must implement certain methods

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DataObjectBean.javaDataObjectBeanDemo.xsp

Filtering and Sorting

• Goal is to store information in the bean to allow fast filtering and sorting

• Base storage is a LinkedHashMap

– Key is the city name

– Values are an ArrayList

• The ArrayList holds a Person object

–First and last name, city, state, email, etc.

–Universal doc id to retrieve Notes document

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Data Model

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Houston

LinkedHashMap<String,ArrayList<Person>> customers

Key is City Name

Lorie Mason

Brad Hunt

Jessie Lang

Mark Travis

firstNamelastNameCityStateeMailNotes IDDocUNID

Person ObjectDallas

Austin

ArrayList<Person>

The customers HashMapstores all the people from a selected state

More on Filtering and Sorting

• Methods of the Bean are used to:

– Return data as an ArrayList to a Repeat

• Sorted (last name, city, email)

• Filter on a city or show all

– Switch to a different state

– Get the cities for the selected state (unique, ordered)

– Store information like:

• City filter

• Desired sorting

• Ascending or Descending sorting

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ReportBean.javaReportBeanDemo.xsp

Homework and Resources

• TLCC’s Java Classes (two)http://www.tlcc.com/admin/tlccsite.nsf/coursedetails.xsp?ccode=ND9XJVKPG

• My Session on Xpages Performance (recorded)

– October, 2015http://www.tlcc.com/admin/tlccsite.nsf/pages/recorded-xpages-webinars?opendocument

• List of Collections with a summary of features– http://www.janeve.me/articles/which-java-collection-to-use

• The Sun Java documentation (version 6, aka 1.6)

• StackOverflow

• Google!!!

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