Study Guide for Intermediate Java Developers

Transcription

1 Study Guide for Intermediate Java Developers After you've completed a beginner class, and begin expanding your skills to include application development, there are a whole bunch of new topics you'll need to learn about. Books to teach these topics vary in quality, so you may be piecing together learning from a mix of online sources, hands-on practice projects, and others' example code. This guide provides a list of topics, and some questions you'll need to be able to answer for each of them. Use it to direct your study time and determine your own approach to learning the topics. This list of questions is meant to help you be more independent in your learning, instead of waiting on an instructor's availability. The questions are not comprehensive. They are meant to guide your attention to important core concepts for each area, moving "unknown unknowns" (you don't know what there is to learn) to "known unknowns" (you are aware of what you don't know so you can begin to learn it). You will come across interesting side details as you research; read those too. Build out your conceptual understanding and vocabulary. You'll also have to do additional research to work out the exact details of each piece of code. You are meant to look up some of the answers to these online, and to build your own understanding by experiencing it hands-on. Use any learning resources you can find. Study Guide for Intermediate Java Developers Page 1

2 Contents 1. Installing Java and Installing and Using Eclipse User Interface Design and UI Elements Event-Driven Programming Data Storage and Databases Using Java with SQL and Databases Layers of Code in an Application Design Patterns and Data Access Objects Exception Handling and Logging Maven and Dependency Managements Using Git and GitHub.com About Web Development with Java Web Milestones 1: Web Server, HTML, and URLs Web Milestones 2: Request, Response, and Definition of Servlet Web Milestones 3: Servlets and JSPs Web Milestone 4: Servlets and DAOs Web Milestones 5: Login Sessions Study Guide for Intermediate Java Developers Page 2

3 1. Installing Java and Installing and Using Eclipse What is the difference between Java EE and Java SE? What is the difference between 'java' and 'javac'? What is the difference between a Java SDK and a JRE? What is a Java jar file? How do you get a command window or terminal window in your operating system? What is a command line? How does your operating system know what paths to search for a program run at the command line? How can you add java to your search path? What is a Java classpath? How do a path and a classpath differ? What is an Eclipse workspace? Within Eclipse, what is a project? What is a source folder? Create a new Java Project inside Eclipse. What does it give you by default? Where should you add your own code? Within your new project, add a simple class with a main() method that prints Hello World or similar. Intentionally create a compile error. In which two locations do the error details show up? What happens if you double-click on an error message? What happens if you hover over an error indicator? Look closely at the file name within the project or package explorer tab. Notice the tiny colored indicator icons on the file name icon. How does the icon change when the file compiles correctly versus when it has an error? Now that you have a short Java class with a main method, how do you make Eclipse run your program? When you run it, where does the output go? What is the console tab? When would it be used? If multiple consoles are open, how would you switch between them? Write a program that runs for a long time or has an infinite loop. Once you started it running, how would you interrupt it or cancel the run? Try it. What is a project wizard? What kinds of wizards are available? What is 'ant'? What is 'maven'? How do they differ? In Eclipse, what is the project explorer tab? What is the package explorer tab? How do they differ? Study Guide for Intermediate Java Developers Page 3

4 What is an Eclipse view? How does the Java view differ from the Debug view? How can you switch between them? How do you set a breakpoint and step through code in a debugger? Eclipse has the ability to click on a function call as if it's a hyperlink, and go to the place where that function is defined. What keys and mouse movement must you use to make the hyperlink show up? What is the Eclipse Outline view, and when might it be useful? How can you make the console word-wrap so the lines aren't so wide? Right-click a file in a project. Notice the "Open" and "Open With" items in the right-click menu. What options does "Open With" provide, and when might you want to use them? Right-click a project, or a file within it, and choose "Properties". What does the "Location:" info tell you? Double-click to open a few different Java source code files or other files in a project. Then, in the project explorer, or package explorer, look for the yellow double arrow icon (middle-top), and click it. Click between the open tabs of source code, and watch what happens in the project/package explorer. How would you describe this behavior? When might it be useful? Press Shift-Command-T (mac) or Shift-Control-T (windows). This is the Open Type dialog. Enter the name of a valid Java class and tell it okay. What does it do? Try it again, and give it an invalid Java class name. What does it do? Give it the name of one of your Java classes from your project. What does it do? Open a Java source file. There is a command to auto-format the source code, fixing the layout. Which menu is it in? What is the keyboard shortcut to it? An Eclipse project view shows a slightly different set of directories and files compared with what's actually on the file system (as seen in a windows or mac file explorer window). What shows up in one but not the other? In Eclipse, how can you change which files are filtered out from the view? In an Eclipse project, what is the.project file for? What is the.classpath file for? What is the.settings directory for? Right click a project, and choose Build Path, Configure Build Path. Examine the tabs and options. This dialog affects the contents of the.classpath file for the project. What is the Libraries tab for? Eclipse Capstone: Write a non-trivial Java program in an Eclipse java project. Run it and debug it until it works. It's fine to reuse code you've written before and move it into Eclipse and test it from there. If you reuse code, try adding a feature, so you get a little more hands-on practice with Eclipse. Study Guide for Intermediate Java Developers Page 4

5 2. User Interface Design and UI Elements What is a graphical user interface (GUI)? Checkbox and dropdown are two examples of user interface elements (things we click on to do stuff). What are some other examples of UI elements? What kinds of UI elements are used for navigating web pages? When might you prefer a dropdown over a textbox? When might you prefer a radio button group or a checkbox? Consider an online store that sells products through their web page. They provide a view that is a list of their products, and a view that is a single product with its details. What kinds of things are typically shown in the list view? What kinds of things are typically shown in the detail view? You're ordering from an online store and forget to fill in a required field. How does the web page tell you about your mistake? When have you used a page that was very confusing about this? When have you used a page that did a good job of helping you see and correct the mistake? What was different about the user interface between the bad and the good? How do web page user interfaces deal with extremely long lists of products or search results? If there were over ten thousand matches, what would help a user navigate the items more effectively? Most data-handling applications provide features for Create, Read, Update, Delete for each kind of data they store. (This is abbreviated CRUD.) What user interface strategies are common for creating/adding a piece of data? What UI layout strategies are common for reading/showing one item or a list of items? What UI layout strategies are common for updating an existing item? What UI layout strategies are common for deleting an item? You can look around the internet for examples, but focus on simpler online stores like shoe stores, not Facebook or Amazon (which have super-complex UIs). Consider an online store that sells physical products (like shoes). What features would a customer expect to use for shopping? What features would a staff member need to use to maintain the site, update products, and fulfill orders? What features would a business owner or accountant use? Study Guide for Intermediate Java Developers Page 5

6 The web page lists out the elements of design as used in art, and you can find more examples of each topic on other sites as well. For each of the principles (balance, gradation, repetition, contrast, harmony, dominance, unity) find a web page that demonstrates that principle either very well or very poorly. (If you're lost on where to look, start at news sites.) If a web site uses that principle poorly, write a sentence or two about how you would improve their design. Where is hierarchy used in web pages as a design principle? How does it help a user? UI Capstone: Pick a web site you like to use. What user interface elements are present? What design principles are used? How is hierarchy used? Why is the front page designed the way it is? What aspects of the user interface help the site be effective? Write 1-2 pages describing the user interface design choices they made and why those choices work. Identify one feature you wish worked differently, and describe why you would change it, and how it would work instead. Study Guide for Intermediate Java Developers Page 6

7 3. Event-Driven Programming Events are an interrupt-driven approach to activities. An event can be user-generated (such as pressing a key, clicking a mouse, or plugging in a network cable) or the event can be system-generated (such as receiving a push notification or a message that the laptop battery is running low). A method that provides code, which runs when an event happens, is called a listener for that event. Events are used in desktop GUIs as well as web page GUIs, and across many programming languages. We'll focus on the web because it's fairly easy to get started and well documented online. Spend some time learning HTML and CSS. The rest of these questions assume basic familiarity with HTML markup and HTML form elements. How does event-driven programming differ from a Java app with a main() method? (You might have to come back to this after experimenting with the topics below.) What HTML elements can trigger an onclick event? What HTML elements can trigger an onchange event? How do you add Javascript code to an HTML web page? How would you write a Javascript function that listens for an onclick event? Write a web page with at least two buttons that do different things when clicked. How does an html form's submit button behave differently with and without an onclick event? What if the listener returns false versus returns true? What is the HTML DOM? How can you change the contents of an html dom element using Javascript? Try changing the text displayed in a paragraph. What is AJAX? What is XML? How are XML and HTML similar and different? What is JSON? What is jquery? Why is it better than plain javascript? Event-Driven Capstone: Write a web page with two dropdowns. The first dropdown should be enabled, while the second is disabled. When a user picks an item from the first dropdown, the second drop populates with options relevant to that (for instance, after picking State, the user may now choose a City) and becomes enabled. When the user clicks a Save button, text elsewhere on the page is updated to reflect their dropdown choices. Study Guide for Intermediate Java Developers Page 7

8 4. Data Storage and Databases What is a server? What is a client? What is a database? What is a database server? What is a database client? What is a database connection? What is SQL (Structured Query Language)? What is a database table? What is a database table column? row? How do you create a table? What data types does MySQL support? How do you insert data into a table? What is a SQL query? What is a where clause? What is a select statement? How do you retrieve all rows from a database table? How do you retrieve rows that match a certain value? How do you retrieve just one row? What is a primary key? What is a foreign key? How do you insert a row with an autogenerated primary key? If one item (such as person name) relates to multiple of another item (such as phone numbers), how do you store both? What is a join? How do you retrieve related data from two tables? What is a left join, and when would you use it? How do you create a row of data that has a value missing in a particular column? How do you delete data from a table? How do you update a value in a given row? Why do primary keys use numbers instead of business-meaning data? Study Guide for Intermediate Java Developers Page 8

9 What is a cascading delete? What is an orphan? Why is cascading behavior important? What is database normalization? In normalized databases, what is third normal form and why is it useful? Design a set of database tables, on paper, for a simple online shoe store. What tables make sense? What primary keys and foreign keys did you end up needing? What questions or uncertainties did you have? Don't worry about making it perfect - this is about discovering the depth of your understanding and the current limits of your knowledge. How would you query for information across 3 different tables that are related by foreign keys? How would you count the number of rows that match a given where clause? What is a group-by statement, and how can you use it to count within each group of rows? How do you name the column in the results, that contains the count? How do you control the sort order that rows come back in? Can you sort by more than one column? Can you reverse the sort order? What is a subquery? What is an explain plan? What is an indexed column? What is an index? Where online can you find an interactive SQL tutorial with practice queries? What section of the online MySQL manual contains the SQL command reference? What kinds of reference charts does visibone.com provide? Is there enough detail in the close-up views to be useful to you? Where else can you find reference sheets online? What areas do you need hands-on practice with, to be comfortable designing database tables, inserting, updating, and retrieving data, and designing for an application? What is a transaction? What do commit and rollback mean? SQL Capstone: Create a database with at least 4 tables, some of which refer to others by foreign key. Insert sample data into every table. Write a few queries that bring back data in a meaningful way for users of that database. Study Guide for Intermediate Java Developers Page 9

10 5. Using Java with SQL and Databases The MySQL database driver for Java JDBC is called Connector/J. It might be included in your download when you install MySQL Community Edition, or you might need to download it separately from What is JDBC? The java.sql.* package provides interfaces while the driver provides an implementation. Why might this extra layer of abstraction be useful? (Hint: Consider other databases.) How do you add the mysql driver jar file to your Eclipse Project's classpath or build path? What do you need to import in your Java code, in order to open a connection to a database? How do you open a connection to the database from Java code? What is a Connection (java class)? What is a Statement (java class)? What is a ResultSet (java class)? How do you use these classes to run a SQL select statement? What exceptions can database code throw? Why might each happen? What's the best way to use a try-finally block to ensure that the result set and the connection are closed properly even if an exception occurs? What is a PreparedStatement, and why is it better than Statement? How do you updating existing data using a PreparedStatement? Stub out a Java method that does this. How do you insert data using a PreparedStatement? Stub out a Java method that does this. When you insert data using jdbc, how do you retrieve the value of the autogenerated primary key? How do you run a select query from java code, and retrieve the results? Does the ResultSet use column names or column numbers to get a value back? What Java data types match which MySQL data types? How do you retrieve just the first 10 rows of a result set? Study Guide for Intermediate Java Developers Page 10

11 How do you retrieve just rows of a result set? If you're providing search results one page at a time (for instance, rows of 800 results), why is it important to have the results in a consistent sort oder? How are transactions used from JDBC? What is autocommit? How do try-finally blocks relate to transactions? If you write Java code in several classes that all talk to the database, how can you simplify and reduce duplication of code for creating a database connection? Ideally your username/password and database URL should only appear in your code once. JDBC Capstone: For the SQL capstone project you did previously, write a Java class to create connections to the database, and a separate Java class to run the queries you created. Make sure everything connects, runs, and works, and that you close your database connection correctly even if a SQL Exception occurs. Ask a mentor for a code review when you are done. Study Guide for Intermediate Java Developers Page 11

12 6. Layers of Code in an Application As applications grow more complex, it becomes useful to separate code carefully based on separation of responsibilities and primary function. A common strategy you'll see is as follows: User Interface Navigation and Menus Customer Features and Data Entry Data Transformation and Validation Business Logic Error Checking Data Persistence Save to database or file Retrieve data when requested Business Domain Data Model The data model of the business domain is all of the pieces of business-related data, such as Customer, Product, Coupon for an online store, or such as Student, Semester, Course for a school. This is often abbreviated "domain model". Why would a domain model object such as Course be used across all 3 layers of Java code? (What is its purpose in the user interface representation? What is its purpose in data persistence? Why might it need to go through data validation in between?) If we didn't split the Java code into these layers, what might that do to the code? No capstone for this one; it's just introducing the concept. Study Guide for Intermediate Java Developers Page 12

13 7. Design Patterns and Data Access Objects What is a software design pattern? What is the GoF (gang of four) design pattern book? Why is it a classic? Can you find a list of those design patterns for free online somewhere? What are Java enterprise design patterns? What is the data access object (DAO) pattern? What methods would typically exist in a Java JDBC DAO class that works with objects from a single database table? How can a DAO tell whether an object it ought to save is the insert of a new row or an update of an existing row? What should the method signature be for a delete method in a DAO? What kinds of exceptions should a DAO throw? How should it report errors? If you find multiple strategies, identify the strengths and weaknesses of each. DAO Capstone: Implement a Java console app (text-only user interface) that lets a user add rows to a database table, choose a row to edit and save those changes, delete a row, and show a list of rows. Also provide a search feature where the user can search by partial text match in one of the columns (such as "Super Duper Shoes" should match a search for "Shoes"). Remember to keep your user interface logic separate from your DAO class that's handling the database. Ask a mentor for a code review when you're done. Study Guide for Intermediate Java Developers Page 13

14 8. Exception Handling and Logging Examine the Java class hierarchy (in the Java API docs) for Exception, Throwable, and RuntimeException. What class is at the root of the hierarchy? What is the difference between those 3 kinds of exceptions? What are checked and unchecked exceptions? How do they differ? What is the parent of SQLException? (Or, if appropriate, the grandparent/etc.) What is the parent/grandparent of NumberFormatException? How do you throw a new exception? Try writing code that does this. How do you catch a SQLException? Try writing code that does this. How do you catch an exception and wrap it in a RuntimeException and then throw that? How do you print out the message and the stack trace of an exception? What sorts of exceptions should code catch and handle itself? What sorts of exceptions should bubble up to the calling class and be handled at a higher level for the whole application? What sorts of exceptions should not be caught at all? Consider code that throws both Exception and some subclass of Exception (such as SQLException). You write two catch { } blocks, one for each type. Why does the order of the catch blocks matter? What will happen if you put them in the wrong order? What is log4j? What is a log4j configuration file? Within log4j, what are logging levels (debug, info, warn, etc) and when should you use each level? How would a log4j configuration file be found by your Java application, when the application runs? How do you print through the logger instead of using System.out.println()? What are the advantages of printing through a logger? How do you log an exception? Logging Capstone: Add logging to your JDBC capstone work. Log when each DAO method is called, and any errors/exceptions. Log when the program starts and ends. Study Guide for Intermediate Java Developers Page 14

15 9. Maven and Dependency Managements What is the ant build tool? What is the maven build tool? How are they similar and different? What is a pom.xml file? What are maven build targets? Which targets are commonly used and what do they each do? What is a maven repository? What is maven central? Install and/or configure maven with Eclipse. Create a java project that has the maven facet or feature enabled. (You might need help with this part.) Create a simple Java main class, and then build the project with 'maven package' through Eclipse. Ensure it compiles and packaging is successful. Add the MySQL driver to the pom.xml dependencies, and rerun maven package. Within your maven-enabled Java project, look in the package explorer for the "Maven Dependencies" item. What kinds of things are listed in here? Add log4j to your dependencies, and rerun maven package. Can you see it show up in the Maven Dependencies within Eclipse? (You might need to right-click your project and choose Refresh.) Double-click the pom.xml to open it in Eclipse, and click into the Source tab (instead of the design view). Make sure you can find this for editing the file later. When you run maven package, where does it output the resulting jar file? Where can you find documentation on how to use maven? Maven Capstone: Convert your JDBC + logging project to use maven instead of adding the jdbc jar file and the log4j jar file directly to your classpath. Remove the jar files for those previous copies. Make sure Eclipse is picking up the maven features on your project, and that your project still runs properly. Study Guide for Intermediate Java Developers Page 15

16 10. Using Git and GitHub.com What is source code revision control? Why is it useful when teams work on code together? Why is it useful when individuals work on code solo? What is the git software? Who created git? Does it have a corporate sponsor? What is the github.com website, and what does it provide for its users? What is an ssh key? Why does github.com encourage using ssh keys for identity rather than username and password? If you use Mac, you already have git software installed. If you use windows, go explore git bash and install it. Where can you find online, hands-on git tutorials? Work through some practices. Set up your ssh key identity for github.com, getting help if you need it. Create a blank repository on github.com, and clone it down to your laptop. Add two files to it, with some text in them. Commit the files and then git push. Refresh to see your changes on the website. Make another change, another commit, and another push. Then use git log to see a list of your commits, and git show <SHA hash> to view the contents of one of your changes. Git Capstone: Add your JDBC + logging + maven project to your github.com account. Optionally, create a somewhat more fully-featured jdbc application with a text-only user interface, if you want more hands-on practice with all the code concepts we've just covered. When you've completed these application-building background work, then you are ready for an introduction to web applications with CGI, http protocol, servlets, and jsps. Study Guide for Intermediate Java Developers Page 16

17 11. About Web Development with Java This next set of sections won't be quite as detailed as the sections you've just been through. You are meant to take your time exploring this, and eventually practicing on a project. The end result will be a project that uses a web user interface, a SQL database back end, and servlets and jsps in the middle to move data around and act as traffic cop. There are many layers of detail to this process, so it's going to take time to learn it. Expect to spend longer on this section than you did on all of the prior study guide combined. Again, you may use any resources you find online, or books, or video courses, etc. Do pay attention to the "servlet api spec" number, (3.0, 3.1, etc.) because this slightly influences what features are available to your code and how examples work. Combining examples from different versions might give you unexpected and frustrating results. The Luv2Code JSP and Servlet tutorial is a paid online class (not affiliated with LaunchCode) that you might find helpful during this section. SPECIAL-BLOG Study Guide for Intermediate Java Developers Page 17

18 12. Web Milestones 1: Web Server, HTML, and URLs I have Tomcat or Jetty installed, and I know how to start and stop my web server. I have an Eclipse "Java Web Project" configured to run on my web server. I can navigate to a URL that loads an html page from my WebContent or webapp folder. I understand the URL paths for static content (html, images, css) and the difference between absolute and relative URLs. I can answer questions about what folder in my project would correspond to a newly invented URL path. I can produce an HTML web site with multiple pages and navigate between them using hyperlinks. The web site does not use any dynamic data. I can get a separate CSS file to load inside my page, and I can include an image. I can answer questions about the file paths and URL paths related to this. Exercise: I have produced a UI mock-up of a form that accepts text fields and a dropdown. I can click the submit button and it goes to the right static page, even though the data fields are not used yet. I can describe the"action" attribute on a <form> tag and explain what it means. Study Guide for Intermediate Java Developers Page 18

19 13. Web Milestones 2: Request, Response, and Definition of Servlet I can describe how a web server examines a URL and uses it to locate a (static) file on disk in a web document directory. I can describe what an HTTP request is and what an HTTP response is. I can describe the purpose of an HTTP response status code, specifically 200, 404, 500, and 403. I can describe the difference between GET and POST requests. I can create and have demoed an HTML page that demonstrates how a browser prompts for resubmit on a POST but does not prompt for resubmit on a GET. I can explain why resubmit could be a problem in certain scenarios. I have examined the contents of an http GET request for a static web page. I have examined the contents of an http POST request resulting from submitting a form with multiple data fields in it. I can extend the HttpServlet class and implement the doget() and dopost() methods to create a servlet class. I can map the servlet to a friendlier URL path using the web.xml file in my project. I understand how URL paths match against the web.xml patterns. In my servlet, I have retrieved the request parameters from the request, and iterated through them, printing them to the console. After that, I have retrieved the PrintWriter from the HttpServletResponse object, and printed the parameters to the output stream instead. I can see my results in a web browser. (No jsps are involved yet, just plain strings from a servlet.) I have tested my servlet with a variety of GET requests and at least one form request which is a POST. Exercise: I have added a second servlet which is meant to do something interesting with the results of the form POST, and modified the form's action url to point to my new servlet. It displays interesting content. (For insatnce, if the form were an contact form, the result of submitting it to the servlet is that a nicely formatted is shown in HTML along with a "Thank you for your submission!"). My servlet is listed in web.xml and works when tested. HTML content should occur within the servlet code; although tedious, this demonstrates the intent of servlets, and we'll fix it shortly. Study Guide for Intermediate Java Developers Page 19

20 14. Web Milestones 3: Servlets and JSPs At this point, you're beginning to see the power of web programming. You can take data from a form, feed it in to a servlet where code gets to run on it, and you get some kind of interesting result based on that data. Now we're going to start chaining together multiple pages like this, and instead of static html files, you will generate every web page through code. Let's see how to take some of the pain out of that. The following explanation is as much for your mentor as for you. It will make sense eventually; take it a small piece at a time. A jsp is a way to move HTML out of the servlet (where it's hard to type) into a template file (where HTML is the norm and it's easy to type). A jsp compiles into a servlet. It can include scriptlet tags to either print the value of a variable, or to run more complex Java code around some HTML (for instance, a loop). Why would we use a servlet vs a jsp? A servlet is for loading data from the database, saving data to the database, and doing data validation. It's the librarian and the traffic cop. A jsp is for presentation logic only. It makes things pretty, but it should not be touching the database directly. The servlet should use a DAO class to load data, put that into the request.setattribute(key, value); and then the jsp loads it from there. A jsp file inside your WEB-INF directory is protected from being served up directly by the web server; it has no URL of its own. Instead, a servlet uses a request dispatcher to hand off the request to the jsp and display the contents. In contrast, a jsp outside the WEB-INF directory works more like a static html file. You can write a URL that loads the jsp directly -- but! no servlet gets any opportunity to run, and so you don't have a good way to load data from a database when you do this. It's poor practice to use DAOs in your jsps. Instead you should send the URL to a servlet first, let it do the heavy lifting, and then the servlet uses the dispatcher to load the jsp. I can create a jsp outside of WEB-INF but inside WebContent (or 'webapp') folder, and I can create a URL that points to it after restarting my web server. My jsp displays simple html text. I can create a jsp inside of WEB-INF, and can prove that I cannot load it via URL, even with a correct path. I can create or modify a servlet so that there is a request dispatcher that displays a jsp. Instead of using the PrintWriter to output html, it now uses only the jsp instead (but goes through a servlet along the way). Study Guide for Intermediate Java Developers Page 20

21 From my servlet, I can generate a random number, put it in the request.setattributes() area, and pull it back out to display it from my JSP code. Reloading the servlet's url generates a new random number. I can modify my exercise from the previous section (form submission) to now use a jsp for display instead of html source code inside the servlet. I can create a servlet whose doget() dispatches to a jsp that shows a form, and whose dopost() accepts the results of that form submission and dispatches to a jsp that shows a pretty layout of the data from that form. The display of the initial form and its results now both come from a servlet, with jsps used for layout. I am ignoring resubmission for now. I can create a servlet whose dopost() method sends a response.sendredirect() to a different servlet's doget() method. I have moved the pretty-layout portion of the response to the new doget() method. I can explain why this avoids the duplicate submission problem if the user presses reload in their browser. I can describe the URLs involved in each step, and the http response codes. This example will become more obvious in the next section when we start working with database data. Intro to JSTL: I understand what basic JSTL tags are available for me to use. I can use JSTL tags in my jsp instead of Java for loops. I can use JSTL to create an href for an <a href> tag. Exercise: I can create a sequence of servlet calls with a multi-page form. There will be 3 form pages and 1 final "thank you" page. The data values from form 1 are carried through into hidden fields in form 2. The data values from forms 1&2 are carried through into hidden fields in form 3. When form 3 submits, page 4 displays the full list of values from forms 1-3 along with a thank you message. I do not lose any values along the way, and use servlets and jsps for each step. Study Guide for Intermediate Java Developers Page 21

22 15. Web Milestone 4: Servlets and DAOs Now that you are starting to get the hang of servlet and jsp urls, hidden form fields, and how to carry data across, it's time to get the database involved. You should have already completed a text-based UI (console) java app that uses JDBC and loads and saves data use the DAO (data access object) design pattern. Review your code and ensure you understand thoroughly how to use DAOs, before you start this section. I can produce a "list" feature using a servlet that loads a list of names and ids from a database table and displays them in a web page (through a jsp). I can add a new attribute to each item in the list: this means a new column in the database, a new member variable in the data bean, and matching changes to the servlet and display logic. I can add a link to each item in the list to display just that item in a "detail" page, where the correct item is loaded (by id) from a database and displayed by itself on screen. I can produce an "add new" feature where the user can fill out a form and press Save, and the servlet will use a DAO to save that data to a database. No error handling yet. After save, my code redirects to a get url, so the user can't actually double-submit. I can produce an "edit" feature where the user can click a link on an item in the list (or a link next to each item), and that individual item is loaded (by id) into a form where the user can modify the values and press Save. When they press Save, the existing item in the database is updated with the new values. The id should never change, but all other fields are acceptable for changes. After save, my code redirects to a get url, so the user can't accidentally double-submit. I can validate required fields are non-empty, in my "add" and "edit" forms, sending the user back to the form with a validation error displayed if they do it wrong. (This can feel tricky at first; be patient as you work it out.) I can provide a "delete" feature for an item in the list. It goes to a confirm page first "Are you sure you want to delete?" with a form and a Cancel and a Yes button. Pressing cancel redirects the user back to the list page. Pressing Yes actually deletes the data and then redirects the user back to the list page. I can provide a "search" feature on my list page, where the search box matches text against the names to limit the results. There is a "Search" button and a "Reset" button. If the user types in a partial name and hits search, it will filter the list results. Pressing reset will blank out the search box and go back to showing the full list of results. Study Guide for Intermediate Java Developers Page 22

23 I can create a bit of Java code that inserts a few hundred items into my database table, so I have sample data to work with. It's okay if they're nonsense. Exercise: I can create a paged navigation in my list, where each item shows no more than 20 items, and there are "next" and "previous" buttons to flip through the pages. I can prove that the first page and a middle page and the last page show exactly the right count of items, no off-by-one errors. (This also takes some DAO work. Be patient!) Study Guide for Intermediate Java Developers Page 23

24 16. Web Milestones 5: Login Sessions You can use multi-page websites, navigate between pages, send data back and forth, do simple database searches, and are becoming fluent in servlet and jsp code. Wouldn't it be nice if your code knew who your users are? This is often a necessary step in building more advanced projects, such as e-commerce sites. I can describe what a session is. (HttpSession, a login session, it has multiple names.) I can describe what caching on disk means, as well as session expiration. I can identify the request and response API methods related to session management. For a modest size project idea, I can create a site map plan for which pages are visible to a guest user, which pages are visible to any signed-in user, and which pages are only usable by an administrative or staff member user. My site map includes page names, page URLs, and a URL scheme that makes it easy to pattern-match the locked pages. I can create a guest home page and a login form, and pre-create a few users in the database. I can make my login form demonstrably log in the user and start their session. Further calls to other servlets show that the user remains logged in. I can reject bad passwords with an appropriate validation error message. My passwords are stored hashed in the database, not plain text. I can describe why this is important. I can explain the difference between encryption and a cypher. I can make the logout link demonstrably log out the user, ending their session. Further calls to other servlets show that the user remains logged out. I can identify users as normal users versus administrators, in my database table. I can show in a servlet which type of user they are. I can reject normal users from administrator-only pages and features. An administrator has a page to reset the password of a normal user (since we don't have the ability to send password reset s - those rquire a mail server). I can send a "Remember Me" cookie to a user so that the username fills in automatically. I can describe what a cookie is and how it's used. Exercise: I can demo a series of user use cases involving logging in, performing some work, logging out, changing users, logging in as the new user, performing Study Guide for Intermediate Java Developers Page 24

25 work, and logging back out. I can demonstrate that the correct user is the only one logged in at each step. Congratulations - you have all the basic skills to create your own web project with a database behind it. Go build cool things! Study Guide for Intermediate Java Developers Page 25