Java ain't scary - introducing Java to PL/SQL Developers

AMIS - 5th April 2012JAVA AIN‟T SCARYINTRODUCING JAVA TO PL/SQLPROGRAMMERS

OVERVIEW• Hello World!• Running Java on the JVM• Language basics: Methods, Variables & simple Types• Debugging• Quiz• Dinner• Introduction to Java Objects• A little inheritance• Scratching the surface of – Java to Database communication (JDBC) – Http to Java communication (Servlet)

HELLO WORLD• Create a PL/SQL program • Create a Java program unit that writes Hello unit that writes Hello World! to the system World! to the system output outputprocedure hello_world void hello_world()isbegin { dbms_output.put_line(Hello World!); System.out.println("Hello World!");end; }

THE CONTEXT FOR THE HELLO_WORLD PROGRAM UNIT• Create the PL/SQL • Create the Java Class Package that contains the that contains the hello_world program unit helloWorld program unitcreate or replace package nl.amis;package welcome public class Welcome {procedure hello_world; public void helloWorld()end welcome; -- end specification { System.out.println("Hello World!");create or replace }package body welcome }procedure hello_worldisbegin dbms_output.put_line(Hello World!);end;end welcome; -- end body

HOW TO RUN THE HELLO_WORLDPROGRAM UNIT (PL/SQL)• In the context of a database connection, invoke the procedure through the package specification begin welcome.hello_world; end;

PL/SQL VM(Oracle7, 1993) PL/SQL VM

PL/SQL VIRTUAL MACHINE• Ever since Oracle7, the Oracle RDBMS contains a PL/SQL Virtual Machine• That means: write [PL/SQL] once, run anywhere (as long as the RDBMS is running)• This portability of PL/SQL across platforms is pretty extraordinary! PL/SQL

JAVA VIRTUAL MACHINE (JVM)• Java is executed by the JVM (Java Virtual Machine)• On almost any platform, a platform specific JVM is available• Java is written once, then executed unchanged on the JVM on the target platform• „write once, run anywhere‟ was the tagline for Java Java

HOW TO RUN THE HELLOWORLD PROGRAMUNIT (JAVA)• Start JVM and instruct it to run a Java Class – More specifically: to invoke the main method of the designated Java Class: java nl.amis.Welcome package nl.amis; public class Welcome { public static void helloWorld() { System.out.println("Hello World!"); } public static void main(String[] args) { Welcome.helloWorld(); } }• In JDeveloper: CTRL + F11

RUNNING HELLO_WORLD• Connect to PLSQL VM • Start JVM and execute (i.e. the database) and main method execute anonymous PL/SQL block ... public static void main(String[] args)begin { welcome.hello_world; Welcome.helloWorld();end; } ...

ABOUT THE JVM• Java is compiled at design time into byte code – held in .class files (one .class per .java file)• The platform specific JVM loads class files (from .class or from JAR• Note: byte code (classes) can be created in other ways too besides from Java code – For example from Groovy, JRuby, BeanShell, Jython and various other languages – The JVM is not correctly named!

ABOUT THE JVM (2)• Byte code is not machine language: the platform independent byte code is interpreted in the target JVM and turned into platform specific actions• Note: Byte code („class files‟) can be decompiled• Note: there is no „dynamic Java‟ such as execute immediate „Java fragment‟

HABITAT OF THE JVM

CLASS• Program Unit for Java – Similar to PL/SQL package• Class with Main method can be executed – Other classes and methods only invoked from within Java code• Execute means: having JVM load, instantiate & invoke• In JDeveloper, run means – Compile Java code (.java) into byte code (.class) – Call Java run time (JVM) with instruction to execute class • Which in turn means: invoke main method of the class

METHODS• Functions are called methods• A method that does not return a value (a procedure in PL/SQL terms) is defined with void as return type: public void helloWorld() { System.out.println("Hello World!"); }• Methods can be public, protected, default or private – Determining accessibility from outside class and from outside package (similar to PL/SQL’s package specification and body)

SOME LINGO AND OTHERJAVA TID BITS• Java is case sensitive• It is common practice to use „camel case‟ for naming classes, methods and variables (and not underscores) public void helloWorld() { System.out.println("Hello World!"); { } }• { and } are used to indicate the start and end of code segments (where PL/SQL uses begin and end) – Such as methods, nested blocks in if, else, loops etc. – {} can be empty (similar to PL/SQL: begin null; end;)• Note: the indentation is not meaningful to the Java compiler – only to the human eye

SOME STRIKING – AND UNIMPORTANT – DISTINCTIONS BETWEEN JAVA AND PL/SQL PL/SQL Java • Java Assignment := = Equality = == String concatenation || + String quoting " IF construct if then [else ] end if if () {} [else {}] Logical operators AND , OR, NOT &&, ||, ! Comment -- and /* … */ // and /* … */l_name varchar2(20):= John; { -- nice name is it not? // what wonderful name this isbegin String name = "John"; if l_name = Hank if (name == "Hank") { then name = name + "B."; l_name:= l_name || B.; } end if; }end;

VARIABLES• Global – defined (anywhere) at class level – accessible from any method – class level variables can be public – meaning they are accessible from outside the class• Local – defined (anywhere) inside a method – only accessible within the method package nl.amis; public class Welcome { private String lastName = "Doe"; public String greeting = "Hello"; public static void helloWorld() { String firstName = "John"; System.out.println(greeting + firstName + lastName); } }

VARIABLES• Definition of a variable is reversed compared to PL/SQL: – first the type then the name• variables are not constrained through their definition (such as VARCHAR2(250) in PL/SQL)• some native types have built-in limitations: byte, short, integer, long, float, double, boolean package nl.amis; public class Welcome { byte smallNumber = 127; short notThatShort = 32767; // 16 bits int substantialNumber = 2147483647; // 32 bits long potentiallyLargeNumber = 0; // 64 bits, 9,2 trillion // floating point values: float fractured = 0.1f; // single-precision 32-bit, e+38 double verySmallAndVeryLarge = -0.1; // 64 bits, e+308 boolean itsNotALie = false; }

PRINT THE FACTORIALS FOR 1..10 create or replace package body factorials as function factorial(p_i in number)PL/SQL return numberbegin is factorials.main(10); beginend; if (p_i<2) then return 1; else return p_i * factorial(p_i-1); end if; end factorial; procedure printFactorials(p_upper in number) is begin for i in 0..p_upper loop dbms_output.put_line(i || ! = || factorial(i)); end loop;create or replace end printFactorials;package factorialsas procedure main(p_upper in number) is procedure main begin (p_upper in number); Factorials.printFactorials(10); end main;end factorials; end factorials;

PRINT THE FACTORIALS FOR 1..10Java java.exe public class Factorials { -classpath C:JavaAintScaryclasses private static int factorial(int i) { nl.amis.Factorials if (i<2) return 1; else return i * factorial(i-1); } private static void printFactorials( int upper) { for (int i=0; i<upper; i++) { System.out.println ( i + "! = " + factorial(i)); } } public static void main(String[] args) { Factorials.printFactorials(10); } }

PRINT THE FACTORIALS FOR 1..10PL/SQL Javacreate package body factorials as public class Factorials { function factorial(p_i in number) private static int factorial(int i) { return number is if (i<2) begin return 1; if (p_i<2) else then return 1; return i * factorial(i-1); else return p_i * factorial(p_i-1); } end if; end factorial; procedure printFactorials private static void printFactorials (p_upper in number) is ( int upper) { begin for (int i=0; i<upper; i++) { for i in 0..p_upper loop System.out.println dbms_output.put_line(i || ! = ( i + "! = " + factorial(i)); || factorial(i)); } end loop; } end printFactorials; procedure main(p_upper in number) is public static void main(String[] args) begin { Factorials.printFactorials(10); Factorials.printFactorials(10); end main; }end factorials; }

DEBUGGING JAVA IN JDEVELOPER• Java code running in a JVM can be remote debugged• That means for example that JDeveloper can listen in to the execution of Java classes and methods – Pausing at breakpoints – Inspecting objects and variables – Inspecting the call stack – Manipulating values – Changing code ‘on the fly’

DEBUGGING IN ACTION

SOME LOOPING CONSTRUCTSPL/SQL Javadeclare { i number := 0; int i = 0; f number := 1; int f = 1;begin loop for (; ; ) { -- alternative: // alternative -- while i < 10 loop // while (i<10) do { dbms_output.put_line System.out.println(i + "! = " + f); (i || ! = || f); if (i == 9) exit when i = 9; -- not needed break; // not needed -- when using the while loop // when using the while loop i:= i+ 1; i++; if i=1 if (i == 1) then continue; continue; -- 11g command end if; f:= f * i; f = f * i; end loop; } //forend; }

SOME LOOPING CONSTRUCTSPL/SQL Javadeclare { step number := 2; for (int i = 10; i>1 ; i=i-2) {begin System.out.println(i); -- print numbers 10, 8, 6, 4, 2 } for i in reverse 1..5 loop } -- STEP does not exist in PL/SQL -- for i in reverse 1..5 step 2 loop dbms_output.put_line(i*step ); end loop;end;

OTHER LANGUAGE CONSTRUCTSPL/SQL Java function divide( p_a in number private static float divide( int a,int b) { , p_b in number) try { return number is return a/b; BEGIN } catch (ArithmeticException ae) { return p_a / p_b; System.out.println(ae.getMessage()); EXCEPTION throw ae; WHEN ZERO_DIVIDE } THEN } dbms_output.put_line (Trying to divide by zero); raise; public static void division() { END; int a = 6, b = 0;DECLARE try { l_a NUMBER := 6; System.out.println("result of l_b NUMBER := 0; division: " + divide(a, b));begin } catch (Exception e) { dbms_output.put_line( result of System.out.println("Some exceptiondivision: || divide(l_a, l_b)); was returned!");exception } when others } then dbms_output.put_line ( Some exception was returned!);end;

DECODE…• PL/SQL • Javadeclare l_gender varchar2(1):= F;begin dbms_output.put_line ( decode( l_gender , F,FEMALE ,MALE // using a ternary expression ) ... ); {end; String gender ="F"; System.out.println ( gender=="F" ? "FEMALE" : "MALE"declare ); l_gender varchar2(1):= F; }begin ... dbms_output.put_line ( case l_gender when F then FEMALE else MALE end );end;

THAT BIG THING ABOUT JAVA… Objects….

THE PERSON CLASS:“MOTHER OF MANY OBJECTS”public class Person { private String firstName; private String lastName; private int salary; private String gender; public String displayLabel() { return (gender=="M" ? "Mr." : "Mrs.") + firstName + " " + lastName; }}

QUIZ TIME• What is the meaning of the acronym „JVM‟• What is meant by „write once, run anywhere‟?• In which environments can you run Java?• How do you get from a .java file to a running program doing things?

QUIZ TIME• What is wrong with this Java statement? string label_value = John + Doe ; -- assign name

QUIZ TIME • What is the PL/SQL equivalent of this Java snippet? { int i = 0; for (; ; ) { System.out.println(i++); if (i == 9) break; } } declaredeclare i integer := 0; i number := 0; beginbegin loop loop dbms_output.put_line(i); dbms_output.put_line(i); i:= i+ 1; i:= i+ 1; exit when i = 9; exit when i == 9; declare end loop; end loop; i number := 0; end;end; begin loop dbms_output.put_line(i); i:= i+ 1; if i = 9 then break; end loop; end;

QUIZ TIME• What is wrong with this Java statement? { for (int i = 10; i>1 ; i=i--) { System.Out.println(i); } }

QUIZ TIME • What is the output from running this Java statement? package nl.amis; public class DoIt { private String lastName = "Obama"; public String greeting = "Hello"; public static void main( String[] args) { String firstName = "Michelle"; System.out.println(greeting + "Mrs." + firstName); } }java.exe -classpath C:JavaAintScaryclasses nl.amis.DoIt

DINNER

JAVA OBJECTS

create or replace package thing as beginprocedure set_value dbms_output.put_line(p_value in varchar2); (value = ||thing.get_value); end;function get_valuereturn varchar2;end thing; begin thing.set_value(hello world);create or replace package body thing dbms_output.put_lineas (value = ||thing.get_value);g_value varchar2(100):= VALUE; end;procedure set_value(p_value in varchar2) isbegin g_value := p_value;end set_value; begin dbms_output.put_linefunction get_value return varchar2 is (value = ||thing.get_value);begin end; return g_value;end get_value;begin g_value:= initialized value;end thing;

Package THING get_value set_valueDatabase Session 1 Database Session 2

SEPARATION OF (SHARED) CODE ANDINSTANCE DATA SHARED MEMORY Package THING get_value set_value PER SESSION MEMORY UGA UGA UGA Session 1 Session 2 Session 3 THING.g_value THING.g_value THING.g_value [Hello World] [Goodbye World] [initialized value] Database Database Database Session 1 Session 2 Session 3

PACKAGE AND MULTIPLE USER SESSIONS• Package state is kept in UGA – Different sessions have different state for package globals – Note: with dbms_session.reset_package, all packages in the sessions are ‘de-instantiated’• Global variable is not really global – it means ‘retained across multiple calls in the same user session’ – not across sessions – Note: true global values can be achieved using Globally Accessible Application Context• When a package is first called in a session, its initialization section is executed – And global variables assume default values – The package is ‘instantiated within the session’: the UGA starts to hold values for the globals• Question: what is global about a GLOBAL TEMPORARY TABLE?

THING IN JAVAcreate or replace package thing as public class Thing {procedure set_value(p_value in varchar2); public void setValue(String value) { this.value = value;function get_value }return varchar2; public String getValue() {end thing; return value; }create or replace package body thingasg_value varchar2(100):= VALUE; String value = "VALUE";procedure set_value(p_value in varchar2) isbegin g_value := p_value;end set_value;function get_value return varchar2 isbegin return g_value;end get_value; public Thing() {begin value = "initialized value"; g_value:= initialized value; }end thing; }

public class Thing { public void setValue(String value) {create or replace package thing as this.value = value;procedure set_value }(p_value in varchar2); public String getValue() {function get_value return value;return varchar2; }end thing; String value = "VALUE"; public Thing() { value = "initialized value"; }begin public static void main(String[] args) dbms_output.put_line { (value = ||thing.get_value); Thing thing = new Thing(); thing.set_value(hello world); System.out.println dbms_output.put_line ("value = "+ thing.getValue()); (value = ||thing.get_value); thing.setValue("Hello World");end; System.out.println ("value = "+ thing.getValue()); } }

MULTIPLE THING INSTANCES WITH EACH ITS INSTANCE DATApublic class Thing { public class ThingRunner { public void setValue(String value) { public static void main(String[] args) { this.value = value; Thing thing = new Thing(); } System.out.println ("value = "+ thing.getValue()); public String getValue() { thing.setValue("Hello World"); return value; System.out.println } ("value = "+ thing.getValue()); Thing thing2 = new Thing(); String value = "VALUE"; System.out.println ("value (2) = "+ thing2.getValue()); public Thing() { thing2.setValue("Goodbye World"); value = "initialized value"; System.out.println } ("value (2) = "+ thing2.getValue()); System.out.println} ("value = "+ thing.getValue()); } }

SEPARATION OF (SHARED) CODE ANDINSTANCE DATA SHARED Class THING getValue setValue INSTANCES thing thing 2 value value [Hello World] [Goodbye World]

CLASS AND OBJECTS• A class is like a PL/SQL package: the template for an instance – At run time, the class is instantiated before its methods can be executed• An instantiated class is called:…. an object – During instantiation: members (global variables) are instantiated and initialization code can be executed • The Constructor method Object thing3 Class THING Object thing value getValue value Object thing2 Object thing4 setValue value value• Note: this also applies to objects in the Oracle Database: – Create type as object ….

TRUE GLOBAL IN JAVA• Truly Global means: shared between all instances of a class in a JVM• Anything in Java designated „static‟ is truly global or shared between all objects based on the same class SHARED Class THING static value INSTANCES thing thing 2 value value

TRUE GLOBAL IN JAVApublic class Thing { static String value = "VALUE"; public void setValue(String value) { this.value = value; } public String getValue() { return value; } public Thing() { value = "initialized value"; }} Object thing Class THING value Object thing2static value value

INSTANTIATING A PERSON (OBJECT)public class Person { private String firstName; private String lastName; private int salary; private String gender; public String displayLabel() { return (gender=="M" ? "Mr." : "Mrs." ) + firstName + " " + lastName; }} public static void main(String[] args) { Person p = new Person(); System.out.println(p.displayLabel()); }

INSTANTIATING A PERSON AND SETTING PERSONAL PROPERTIESpublic class Person { private String firstName; private String lastName; private int salary; private String gender; public static void main(String[] args) {public void setFirstName (String firstName) { Person p = new Person(); this.firstName = firstName; p.setFirstName("John");} p.setLastName("Doe"); p.setGender("M");public String getFirstName() { System.out.println(p.displayLabel()); return firstName; }}public void setLastName(String lastName)...// getters and setters for all properties public String displayLabel() { return (gender=="M" ? "Mr." : "Mrs." ) + firstName + " " + lastName; }}

PASSING A PERSON TO A METHODpackage nl.amis;public class PersonalAssistant { public static void printPersonalLabel ( Person person) { System.out.println ( (person.getGender()=="M" ? "Mr." : "Mrs.") + person.getFirstName() + " " + person.getLastName() ); }} public static void main(String[] args) { Person p = new Person(); p.setFirstName("John"); p.setLastName("Doe"); p.setGender("M"); PersonalAssistant.printPersonalLabel(p); }

NOTES ON STATIC METHODS• Methods can be designated static too• Static methods can only access static class members (that means: variables that are also static in the Class)• A static method can be invoked on the Class – you do not first need to instantiate an object public static void main(String[] args) { ... PersonalAssistant.printPersonalLabel(p); } vs. public static void main(String[] args) { ... PersonalAssistant pa = new PersonalAssistant(); pa.printPersonalLabel(p); }

MULTIPLE PEOPLE Class Person … displayLabelpublic static void main(String[] args) { Person p Person p = new Person(); firstName John p.setFirstName("John"); lastName Doe p.setLastName("Doe"); Gender M p.setGender("M"); Person p2 = new Person(); p2.setFirstName("Jane"); Person p2 p2.setLastName("Doe"); firstName Jane p2.setGender("F"); lastName Doe System.out.println(p.displayLabel()); System.out.println(p2.displayLabel()); Gender F}

TWO TYPES OF VARIABLES• Variables can contain a value such as a number or boolean – Primitive types: byte, short, integer, long, float, double, boolean• Variables can also contain a reference to an object – Built-in Classes such as Byte, Short, Integer, Long, Float, Double, Boolean, Dat e – Custom classes such as Person and Thing• String is a special beast: it is an object reference but has also some primitive behavior – For example: create String with simple ...assignment, without new to instantiate a new String String value = "VALUE"; public Thing() { value = "initialized value"; }

METHODS ON THE BUILT-IN STRING CLASS• Methods on a String

METHOD CHAINING • Using various methods on StringString someString = "Hello";someString = someString.concat(" World ");someString = someString.replaceAll("Hello", " Goodbye");someString = someString.toUpperCase();someString = someString.trim();System.out.println(someString); • When a method returns an object, a method can be invoked on that object – and when that method also returns an object ..String someString = "Hello";someString = someString.concat(" World "). replaceAll("Hello", " Goodbye").toUpperCase().trim();System.out.println(someString);

PRIMITIVE VARIABLES AND PARAMETERS• Primitives are just a value 1.2312 FALSE 255 – Assigning one variable to another leads to copying the value 255• Passing a primitive variable as parameter to a method means passing a copy of the value 59182 255 – Primitive parameters are read-only – there is no equivalent to in out or out parameters

OBJECT VARIABLES AND PARAMETERS• Object variables are references to objects <pointer> Person <pointer> Person – Multiple references to the <pointer> same object can exist – When no references exist any longer, the object will be garbage collected (eventually)• Passing an object variable as parameter means passing a read-only copy of the object reference – The object itself is editable! <pointer>

PERSONAL DETAILS• There is more to a Person than a few simple properties Social Profile Person Email Address[es]• Person properties can be – References to other objects (such as a social profile) – Collections of values or object references (such as email addresses)

INTRODUCING CLASS SOCIALPROFILE Social Profile Person Email Address[es]

INTRODUCING CLASS EMAILADDRESS Social Profile Person Email Address[es]

PERSON WITH HIS DETAILS Social Profile Person Email Address[es]

CREATING A COMPLEX PERSONPerson p = new Person("John", "Doe", 4500, "M");p.getSocialProfile().setBlog("http://johndoe.blogspot.com");p.getSocialProfile().setMsn("JohnnyDoe_234");p.getEmailAddresses().add(new EmailAddress("johnny.doe@gmail.com","P"));p.getEmailAddresses().add(new EmailAddress("john.p.doe@acmecorp.com","W")); Social Profile Person Email Address[es]

QUICK COLLECTION OVERVIEW AND COMPARISONdeclare ... type string_tbl_t is List<String> names = table of varchar2(200); new ArrayList<String>(); l_names string_tbl_t:= names.add("Tobias"); string_tbl_t(); names.add("Lex"); l_index number; int index = 1;begin for (String name:names) { l_names.extend(); System.out.println l_names(1):= Tobias; ("Name "+index+++" : "+name); l_names.extend(); }//for l_names(l_names.last):= Lex; l_index:= l_names.first; } loop exit when l_index is null; dbms_output.put_line ( Name ||l_index|| : ||l_names(l_index) ); l_index := l_names.next(l_index); end loop;end;

PERSONAL DETAILS Social Profile Person Email Address[es] Employee Customer

ENTITY RELATIONSHIP MODELING PERSON SOCIAL_PROFILE EMPLOYEE EMAIL_ADDRESS CUSTOMER

OBJECT ORIENTED DESIGN 1 0..1 PERSON SOCIAL_PROFILE 1 0..* EMAIL_ADDRESS EMPLOYEE CUSTOMER

CODE FOR SUB CLASSESpublic class Employee extends Person { private String job; private int departmentId; private Date hiredate; // getters and setters}public class Customer extends Person { private String companyName; private String telephoneNumber; // getters and setters}

PERSONAL ASSISTANT: CAN IT DEALWITH EMPLOYEES AND CUSTOMERS?package nl.amis;public class PersonalAssistant { public static void printPersonalLabel ( Person person) { System.out.println ( (person.getGender()=="M" ? "Mr." : "Mrs.") + person.getFirstName() ? + " " + person.getLastName() ); } public static void main(String[] args) {} Employee e = new Employee(); e.setFirstName("John"); e.setLastName("Doe"); e.setGender("M"); e.setJob("Manager"); PersonalAssistant.printPersonalLabel(e); }

AN INSTANCE OF A SUB CLASS IS ALSO AN INSTANCE OF ITS SUPERCLASS(ES) • Of course each Employee and every Customer is also a Person! • A method that accepts the superclass as input, will be able to process instances of the subclass just fine – Ask for Person, and get Customer or Employee is OK • Note: the reverse is not true: when the required input is a specialized sub type, then a supertype instance is not good enough – Ask for Customer and get a Person is NOT OKpublic static void printEmployeeLabel ( Employee employee) { System.out.println ( employee.getJob() + " in department " + employee.getDepartmentId() Person p = new Person(); ); p.setFirstName("John");} p.setLastName("Doe"); p.setGender("M"); PersonalAssistant.printEmployeeLabel(p);

ANY METHOD & PROPERTY DEFINED ON THESUPERCLASS ALSO EXISTS FOR A SUBCLASS• Properties and methods on Person class are inherited by the subclasses Employee and Customerpublic class Person { private String firstName; private String lastName; private int salary; private String gender; ...public class Employee extends Person { private String job; private int departmentId; private Date hiredate; Employee e = new Employee(); // getters and setters e.setFirstName("John"); e.setLastName("Doe");} e.setGender("M"); e.setJob("Manager"); e.setDepartmentId(10);

OVERRIDING METHODS IN THE SUBCLASS – PROVIDING A SPECIALIZED IMPLEMENTATION • Methods can be overridden in a sub class – the sub class has its own version of the method with the exact same signature – invoking the method on an instance of the sub class results in execution of the specialized implementation – note: the sub class implementation can invoke the super class method too public class Employee extends Person { ... Person public String displayLabel() { return super.displayLabel() + " (" + this.job+")"; }displayLabel() public class Person { ... Employee public String displayLabel() { return (gender=="M" ? "Mr." : "Mrs." )displayLabel() + firstName + " " + lastName; } }

PRINTING THE EMPLOYEE DISPLAYLABEL • The Employee displayLabel method is both – the Employee’s special (overridden) implementation – as well as the super’s (Person’s) original version Person Employee e = new Employee();displayLabel() e.setFirstName("John"); e.setLastName("Doe"); e.setGender("M"); e.setJob("Manager"); Employee e.setDepartmentId(10); System.out.println( e.displayLabel());displayLabel()

IMPERSONATING AN EMPLOYEE?• When a method accepts a handle to a Person object public String personalLabel(Person p) { return p.displayLabel(); }• and it receives a handle to a specialized type of Person – an Employee (no less) Employee e = new Employee(); e.setFirstName("John"); e.setLastName("Doe"); e.setGender("M"); e.setJob("Manager"); e.setDepartmentId(10); System.out.println( personalLabel());• it will invoke the specialized, overridden method

EMPLOYING A PERSON?• When a method accepts a handle to a Person object public String inspectPerson(Person p) { }• it can determine if the Person is just a Person or someone more special… public String inspectPerson(Person p) { if (p instanceof Employee) { return "Employee"; } else if (p instanceof Customer) { return "Customer"; } else { return "Person"; } }

CASTING A PERSON IN THE ROLE OFEMPLOYEE• When a method accepts a handle to a Person object public String inspectPerson(Person p) { }• and it has determined that the Person is someone more special – an Employee – it can also address the Employee capabilities of the Person objectpublic static void printSpecialPersonalLabel ( Person person) { String label = (person.getGender()=="M" ? "Mr." : "Mrs.") + person.getFirstName() + " " + person.getLastName(); if (person instanceof Employee) { label = label + " ("+ ((Employee)person).getJob()+")"; } if (person instanceof Customer) { label = label + " ("+ ((Customer)person).getCompanyName()+")"; } System.out.println(label);}

CASTING IS SIMILAR TO CONVERSION IN PL/SQL • PL/SQL has explicit (to_number, to_char) and implicit conversion – similar to casting in Java declare i varchar2(10) := 21; function add( p1 in number, p2 in varchar2) return number is begin return p1 + p2; end add; begin dbms_output.put_line(add(i,21)); end; • The keyword cast is also explicitly used in PL/SQLdeclare l_timestamp TIMESTAMP := cast (05-Apr-2012 09.00.00.00 PM as TIMESTAMP ); l_number number(2) := cast (21 as number); l_names string_table;begin select cast ( multiset(select ename from emp) as string_table) into l_names from dual;

TECHNICAL OBJECT HIERARCHY• For example: RichTable class from ADF Faces:

DESIGN BY CONTRACT• A contract is specification of the functionality that is (or will be) provided by some implementation – Without stipulating details about how the implementation is done – And sometimes well before the implementation is done• For consumers the contract is enough to create the software that relies on the functionality create or replace package calculator as function add( p1 in number, p2 in number) return number; function multiply( p1 in number, p2 in number) return number; end calculator;

DESIGN BY CONTRACT IN JAVAINTRODUCING THE JAVA INTERFACE• The contract dictating functionality in Java is called an Interface – It defines methods – without providing implementations for those methods package nl.amis public interface Calculator { public int add( int p1, int p2); public int multiply(int p1, int p2); }• Classes can implement no, one or multiple Interfaces – And extend from only one super-class• Any interface can be implemented by multiple classes

CODING TO THE INTERFACE – INVOKING THE INTERFACE WITHOUT IMPLEMENTATION • Classes can invoke the „interface‟ without knowledge about the actual classes that implement the contract public class Worker { private Calculator calculator; // instance of the interface public void tableOfMultiplication( int table) { for (int i=1;i<=10;i++) { System.out.println( i +" * "+ table + " = " + calculator.multiply(i, table)); } }Calculator public void setCalculator(Calculator calculator) { this.calculator = calculator; } public static void main(String[] args) { Worker worker = new Worker(); worker.setCalculator(new SpecialCalculator()); worker.tableOfMultiplication(5); } }

IMPLEMENTING THE INTERFACE• Any class can implement an interface (or more than one) if it publishes the required methods package nl.amis; public class SpecialCalculator extends Object implements Calculator , SecondContract { public int add(int p1, int p2) { return p1 + p2; } public int multiply(int p1, int p2) { return p1 * p2; } // defined in interface SecondContract public String remove(String s1, String s2) { return s1.replaceAll(s2, ""); } } }

LEVERAGE METHODS FROM OTHER INTERFACES AS WELL • Testing if an object implements an interface is done using instanceof • Invoking methods from an interface on an object can be done by casting the object to the interfacepublic class Worker {public static void main(String[] args) { Calculator calculator = new SpecialCalculator(); if (worker.calculator instanceof SecondContract) { System.out.println(((SecondContract)calculator).remove ("HELLO WORLD", "O")); }//if}}

OVERVIEW• Hello World!• Running Java on the JVM• Language basics: Methods, Variables & simple Types• Debugging• Quiz• Dinner• Introduction to Java Objects• A little inheritance• Scratching the surface of – Java to Database communication (JDBC) – Http to Java communication (Servlet)

JAVA APPLICATIONS & DATABASE Cache “NO SQL” JPAPlain JDBC Ibatis, Spring EJB (CMP) WS* Data Grid (Hibernate) JDBC RDBMS

JDBC – JAVA DATABASE CONNECTIVITY• Using a JDBC Driver…• Any Java program can create a connection to almost any relational database – Connecting to a schema using a password, just like Forms, SQL*Plus or an APEX browser session – Note: most databases have their own, special JDBC drivers• Through that connection, the Java program can query, do DML and invoke Stored Procedures and Functions• Java programs can handle long running transactions and sessions

QUERY EMPLOYEE DETAILS • Execute SQL Query via JDBC – process ResultSet:public static void main(String[] args) throws SQLException { Connection connection = ConnectionManager.getConnection(); // Get a statement from the connection Statement stmt = connection.createStatement(); // Execute the query ResultSet rs = stmt.executeQuery("SELECT empno,ename, sal FROM emp"); // Loop through the result set while (rs.next()) { System.out.println(rs.getInt(1) + " : " + rs.getString(2) + " (salary = " + rs.getFloat(3) + ")“ ); }//while // Close the result set, statement // and the connection rs.close(); stmt.close(); connection.close();}

PL/SQL PACKAGE PROCESSING AN HTTPREQUEST: THE EMBEDDED PL/SQL GATEWAY• The Database (the PL/SQL VM) can handle HTTP requests via the Embedded PL/SQL Gateway• HTTP requests are routed to a custom PL/SQL Package that writes the (usually HTML response)• The EPG infrastructure handles the actual HTTP response to the invoker E htp P G Custom PL/SQL package

JAVA CLASS PROCESSING AN HTTPREQUEST: THE SERVLET• The JVM can handle HTTP requests via the Servlet Container• HTTP requests are routed to a custom Java Class that writes the (usually HTML response)• The Servlet infrastructure handles the actual HTTP response to the invoker JVM Greeter WebLogic Server

HELLO WORLD SERVLETpublic class HelloWorldServlet extends HttpServlet {private static final String CONTENT_TYPE = "text/html; charset=utf8";public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType(CONTENT_TYPE); PrintWriter out = response.getWriter(); out.println("<html>"); out.println("<head><title>Hello World</title></head>"); out.println("<body>"); out.println("<h1>Hello World!</h1>"); out.println("</body></html>"); out.close();}}

SERVLET WITH PARAMETERSpublic void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String name =null; Object nameParam = request.getParameter("name"); if (nameParam!=null) { name = (String)nameParam; } response.setContentType(CONTENT_TYPE); PrintWriter out = response.getWriter(); out.println("<html>"); out.println("<head><title>Hello World</title></head>"); out.println("<body>"); if (name!=null) { out.println("<h1>Hello "+name+"!</h1>"); } else { out.println("<h1>Hello World!</h1>"); } out.println("</body></html>"); out.close();}

DEMO OF SERVLET THAT WRITES EMPLOYEES TO THE BROWSER PAGEpublic void doGet(HttpServletRequest request, • HTTP request with department idthrows ServletException, HttpServletResponse response) IOException { • Response is HTML = null; Integer departmentIdentifier page with a list of employees in the department if (request.getParameter("departmentId") != null) { departmentIdentifier = Integer.parseInt(request.getParameter("departmentId")); } List<String> employeeDetails = new EmployeesCoordinator(). getEmployeeDetails(departmentIdentifier); response.setContentType(CONTENT_TYPE); PrintWriter out = response.getWriter(); out.println("<html>"); out.println("<head><title>Employees</title></head>"); out.println("<body>"); out.println("<h1>Employees</h1>"); out.println("<ul>"); for (String employee : employeeDetails) { out.println("<li>" + employee + "</li>"); } out.println("</ul>"); out.println("</body></html>"); out.close();}

DEMO OF SERVLET THAT WRITES EMPLOYEES TO THE BROWSER PAGEpublic class EmployeesCoordinator { public• List<String> getEmployeeDetails(Integer departmentId) { HTTP request with department id List<String> employees = new ArrayList<String>(); • Response is HTML page with a list of employees in Connection connection; the try { department connection = ConnectionManager.getConnection(); PreparedStatement stmt = connection.prepareStatement("SELECT empno,ename, sal FROM emp WHERE deptno = nvl(?, deptno)"); if (departmentId != null) { stmt.setInt(1, departmentId); // set bind parameter value } ResultSet rs = stmt.executeQuery(); // Loop through the result set while (rs.next()) { employees.add( rs.getInt(1) + " : " + rs.getString(2) + " (salary = " + rs.getFloat(3) + ")"); } // while rs.close(); stmt.close(); connection.close(); } catch (SQLException e) {} // when others then null; return employees; }}

SUMMARY• Java is a 3GL programming language – Similar to PL/SQL in many respects• Java runs on a JVM - available on almost any platform – PL/SQL runs on database (PL/SQL VM)• JDeveloper is an IDE (one of many) – Support for edit/refactor/compile/run/debug/…• Java Class contains properties and methods – Just like PL/SQL package• Instances of a Class are called Objects – Each Object has ‘state’ (like PL/SQL package in each database session)• Class can have Sub Classes: more specialized – Sub Classes inherit methods and properties and add (or override) – Similar to Sub Types in ERD

SUMMARY (2)• In Java the contract that specifies the functionality provided by a Class is called Interface – Similar to the PL/SQL Package Specification• An object can be cast in a specific role (to a Class or Interface) if it is an instanceof that Class or Interface – Similar to conversion or casting in PL/SQL• Through JDBC – Java programs can access relational databases and execute SQL & call PL/SQL• Servlets are Java Classes that process HTTP Requests and return HTTP Responses – for example to browser – Similar to PL/SQL packages accessed through EPG (database embedded PL/SQL gateway)

NEXT STEPS• „get your hands dirty‟• Internet• Head First Java• Download & Install JDeveloper from OTN• AMIS Training “Java for PL/SQL Developers” (5 day)

BUT FIRST…

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Java ain't scary - introducing Java to PL/SQL Developers

by Lucas Jellema

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Java ain’t scary - introducing Java to PL/SQL Developers Presentation Transcript