Presentation on Google Guava. Gives a brief overview of Basic Utilities, Strings and Caching in Guava.

1. Gauva – Extension to Java
JUG Hyderabad
Rohit Vaidya

2. Agenda
Basic Utilities Strings
Caching

3. Before you start...
➢ Experience bulding software with Java
➢ Builder Pattern [Item 2 – Effective Java]

4. Annotations
➢ GwtCompatible – Type can be used with GWT
➢ Beta – A public API class,method or field is
subject to change
➢ GwtIncompatible – Cannot be used with GWT
➢ VisibleForTesting – Indicates the visibility of
the type or member has been relaxed to make
code testable

5. Guava – Introduction
➢ Google Guava is open source project released
by Google
➢ Actively used and maintained by google
engineers
➢ Used extensively in open source projects
➢ Not a replacement of Apache commons- you
can continue to use both

6. Why Guava?
➢ The goal is for you to write less code
➢ Make code more readable, cleaner and simpler
➢ Helps developers to focus on business logic
rather than writing java utilities
➢ Saves time, resources and improve productivity
➢ Extension for Java

7. Preconditions
➢ checkArgument(boolean)
➢ Thows IllegalArgumentException
➢ Used to validate argument
➢ checkState(boolean)
➢ Throws IllegalSateException
➢ Used to check Object state
➢ checkNotNull(T)
➢ Throws NullPointerException
➢ Returns the value directly if non null

8. Preconditions
public static boolean isTrue(Boolean value){
checkArgument(value,"You are not passing true.");
return true;
}
isTrue(false);
---
Exception in thread "main" java.lang.IllegalArgumentException:
You are not passing true.
At ...
isTrue(true);
---
Continues gracefully ....

9. Why Preconditions?
➢ Validation
➢ Defensive coding
➢ Each method has three variants
➢ No extra arguments
➢ An extra object for error message
➢ An extra String & Object. GWT compatible.
String.Format like ub only allows %s
➢ Recommned to be used with static imports

10. Preconditions
public static void argOneLessThanArgTwo(int i,int j){
checkArgument(i<j,"%s is not less than %s",i,j);
}
---
Exception in thread "main" java.lang.IllegalArgumentException:
10 is not less than 5
public static boolean checkIfNull(Object foo)
{
checkNotNull(foo);
return true;
}
---
Exception in thread "main" java.lang.NullPointerException

11. Strings
➢ Joiner
Joiner joiner = Joiner.on(" ").skipNulls();
String str = joiner.join("Harry",null,"Potter");
System.out.println(str);
---
Harry Potter

12. Strings
List<String> fruits =
Arrays.asList("Guava","Apple","Mango",null,"Pears");
String fruit = Joiner.on(" ").useForNull("Banana").join(fruits);
System.out.println(fruit);
---
Guava Apple Mango Banana Pears

13. Strings
➢ Splitter - Quiz
String[] str="foo:and:boo".split(":");
for(String s:str)
if(s.isEmpty())
System.out.print("empty ");
else
System.out.print(s+ “ “);
---
1) “empty” ”foo” ”and” ”boo” ”empty”
2) “foo” ”and” ”bar”
3) “foo:and:bar”

14. Strings
Quiz continued:
String[] str="foo:and:boo".split("o");
for(String s:str)
if(s.isEmpty())
System.out.print("empty ");
else
System.out.print(s+ “ “);
---
1) “empty” ”f” ”empty” ”:and:b” ”empty”
2) “foo” ”and” ”bar”
3) “foo:and:bar”
4) “f” “empty” “:and:b”

15. Strings
➢ Java inbuilt splitter has quirky behaviour
➢ Use Guava splitter instead
➢ Makes use of fluent pattern
Iterable<String>splitStr = Splitter.on(",")
.trimResults()
.omitEmptyStrings()
.split("foo,bar,, qux");
---
foobarqux //splitStr if iterated will have foobarqux

16. Strings
➢ CharMatcher
– Utility methods to operate on occurence of
CharSequence type
//Remove digits from the string
CharMatcher.digit().removeFrom("123abc")
---
Abc
//Retain only numbers and upper and lower case characters
CharMatcher.digit()
.or(CharMatcher.javaLowerCase())
.or(CharMatcher.javaUpperCase())
.retainFrom(“@#$@#$@#$Mb:13232546595”);

17. Strings
➢ CharSets
– Similar to StandardCharSet in Java 7
try {
byte[] bytes= num.getBytes("UTF-8");
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
//Use this one instead
byte[] byteContainer= num.getBytes(Charsets.UTF_8);

18. Object Common Methods
➢ Objects.equals [Item9] – Compare in null
sensitive way
➢ Objects.hashCode – Hashing all fields of the
class
➢ toString – MoreObjects.toStringHelper [Item
10 Effective Java Always overide toString]
➢ compare/compareTo – Alternative to direct
implementation of Comparator/Comparable
interfaces

19. Object Common Methods
➢ Equals
Integer x=10;
Integer y=10;
System.out.println(x.equals(y));//true
x=null;
x.equals(y);
---
NPE
//Instead
System.out.println(Objects.equals(null, y));

20. Object Common Methods
➢ HashCode
@Override public int hashCode(){
return Objects.hashCode(rollno,fname,lname);
}
➢ toString
@Override public String toString(){
return MoreObjects.toStringHelper(this)
.add("First Name", this.fname)
.add("Last Name", this.lname)
.add("Roll No", this.rollno)
.toString();
}

21. Object Common Methods
➢ Compare/compareTo
public int compareTo(Person other) {
int cmp = lastName.compareTo(other.lastName);
if (cmp != 0) {
return cmp;
}
cmp = firstName.compareTo(other.firstName);
if (cmp != 0) {
return cmp;
}
return Integer.compare(zipCode, other.zipCode);
}

22. Object Common Methods
➢ Comparison Chain Guava
public int compareTo(Foo that) {
return ComparisonChain.start()
.compare(this.aString, that.aString)
.compare(this.anInt, that.anInt)
.compare(this.anEnum,
that.anEnum,Ordering.natural().nullsLast())
.result();
}

23. Caching
Cache
Application

24. Caching
➢ Guava has on heap key value cache
➢ Implementation is thread safe
➢ No support for distributed caching – Consider
memcached instead

25. Caching
➢ When to consider Gauva cache? (guava wiki)
➢ You are willing to spend some memory to improve
speed.
➢ You expect that keys will sometimes get queried
more than once.
➢ Your cache will not need to store more data than
what would fit in RAM.

26. Caching
➢ Caching Verbs
➢ Populating
➢ Evicting
➢ Refreshing
➢ Types of Cache in Guava
➢ Loading Cache - knows how to load enteries when
a cache miss happens
➢ Cache – Does not automatically load enteries

27. Caching – Population
➢ From a cache Loader
➢ LoadingCache is a Cache built with CacheLoader
➢ CacheLoader knows how to get the keys if the key
is missing
➢ Using Callable
➢ get(K,Callable<K>)
➢ Inserted Directly
➢ Values are inserted directly using cache.put(K,V)

28. Caching
● CacheLoader
–
● CacheLoader
–
➢ CacheLoader
LoadingCache<Integer,Integer> cache =
CacheBuilder.newBuilder()
.maximumSize(20)
.build( new CacheLoader<Integer,Integer>(){
public Integer load(Integer key){
return fibonacii(key);
}
});
public static int fibonacii(int i){
if(i==0||i==1)
return 1;
else
return fibonacii(i-1)+fibonacii(i-2);
}

29. Caching
➢ Quiz
What will be the size of the cache?
LoadingCache<Integer,Integer> cache =
CacheBuilder.newBuilder()
.maximumSize(20)
.build( new CacheLoader<Integer,Integer>(){
public Integer load(Integer key){
return fibonacii(key);
}
});
Cache.get(0);
for(i=0;i<40;i++)
Cache.get(i);

30. Caching
➢ Eviction
➢ We will not have enough memory to cache
everything
➢ Hence eviction is inevitable
➢ Types
➢ Size Based Eviction CacheBuilder.maximumSize(long)
➢ Timed Eviction
➢ CacheBuilder.expireAfterAccess(long,TimeUnit)
➢ CacheBuilder.expireAfterWrite(long,TimeUnit)

31. Caching
➢ Reference Based Eviction
➢ Guava allows you to garbage collect entries by
using weak References for key & values
➢ Soft Refernces for Values
➢ Builders for Refernce based Eviction
➢ CacheBuilder.weakKeys()
➢ CacheBuilder.weakValues()
➢ CacheBuilder.softValues()

32. Caching
➢ Refreshing
➢ Refreshing is not same as eviction
➢ Refreshing a key loads a new value for the key
➢ LoadingCache.refresh(K)

33. References
➢ https://github.com/google/guava/wiki
➢ http://mvnrepository.com/artifact/com.google.guava
➢ Effective Java : Joshua Bloch
➢ Wikipedia : Caching