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As a step up from the last exercise of saving individual parts of a contact to a database, you will now explore how we might store a contact object into the database.
Now that you've seen how to connect to and
interact with
0:00
a database in Java using JDBC,
we're ready to take it to the next level.
0:03
If we're writing a contact
manager application,
0:07
one of the obvious objects we'd want
to work with would be a contact object.
0:10
We can write a POJO.
0:16
Remember, that's plain old Java object.
0:17
That models a contact by creating a class
that includes an instance field for
0:19
each of the database columns we define.
0:23
Then, when we have a new contact object,
0:27
we should be able to simply
save it to the database.
0:29
Let's write a first draft of
what that might look like.
0:32
What I'd like to do here is write a save
method that allows us to quickly save
0:36
a contact to the database without having
to continually rewrite the SQL to do so.
0:40
Let's get this started at the bottom.
0:45
So I'll start by entering a method
stub here, public static void.
0:48
I'll call it save.
0:51
And I'd like to save a cCntact object so
I'll include that as a parameter.
0:52
And let me drop a couple comments in here.
0:57
The things that we'd like to do.
0:59
So we'll start by composing the query,
and then we will execute the query.
1:01
Let's begin composing the query by using
a String variable, I'll name it sql.
1:08
And this variable will hold the general
syntax for an insert statement.
1:13
We wanna insert it into
the contacts table.
1:17
We'll list our column names, and
1:19
then we'll list the actual
values that we'd like to insert.
1:21
So my column names here are firstname,
lastname, email, and phone.
1:24
And what I wanna do is stick placeholders
in here where I can put the actual
1:31
values from my contact object for
the values of the insert statement.
1:36
But, so that I don't forget the single
quotes that surround a string value in
1:41
SQL, I'm gonna stick those in right now.
1:45
The first three columns
are string columns.
1:48
So for our first name we'll
have a string placeholder.
1:52
Same for last name and email.
1:55
And for the phone we'll
have a numeric placeholder.
1:59
Now, let's take the actual values
of the Contact object's fields
2:02
into this string using String.format.
2:07
And I will place or assign that value
right back to the SQL variable.
2:09
So I'll use string String.format.
2:14
The sql variable holds my general format,
and
2:16
then into the placeholders I will place
the values contact.getFirstName(),
2:19
contact.getLastName(), contact.getEmail()
and
2:28
contact.getPhone.
2:36
If you wanna verify that those
getters actually exist are are in
2:39
alignment with the Contact class,
go ahead and
2:43
click on Contact.java to verify
that that is indeed the case.
2:46
In order to execute this update
using statement.executeUpdate,
2:50
we'll need that statement object.
2:54
Let's include it as a parameter
after the Contact object.
2:56
And I will just call this Statement.
3:00
So under execute the query,
I can now call statement.executeUpdate.
3:03
And pass it the value of the sql variable,
3:09
which will hold our fully
formatted insert statement,
3:12
including the values that have been
placed into these placeholders.
3:16
Just one more issue with this method.
3:22
The statement.executeUpdate method is
declared as throwing a SQL Exception.
3:24
So, either we'll need a try
catch block right here,
3:29
which catches the SQL exception.
3:32
Or, we'll have to declare this save
method as throwing the SQL exception,
3:34
which means that the caller of this
method will have to handle this.
3:39
We'll choose this ladder approach,
3:43
since the caller of this method
will be the main method up above.
3:45
And up here in the main method we
already have a try catch that handles
3:49
the SQL exception.
3:53
So let's add that throws
clause right here.
3:55
Throws, SQLException.
3:58
Speaking of that main method, let's return
to that main method and replace these two
4:02
insert statements with calls to
our newly coded save method.
4:08
So the first I'll need to do
is create a Contact object
4:13
with all the same information that's
included in this first insert statement.
4:17
So the order of this, and again,
4:21
you can verify this in
contact.java is first name,
4:25
last name, email, and phone.
4:32
I'm gonna just copy and paste this.
4:37
But this is a long value, so
I won't forget to append the L there so
4:39
the JVM knows to consider it a long.
4:43
Now, I'm ready to call our
newly coded save method.
4:47
So I'll save this contact using the
statement object that I constructed above.
4:51
And we'll repeat all that for
James Gosling as well.
4:57
We'll add him right here, James Gosling.
5:03
James@java.com.
5:10
And I'll use this phone number,
without forgetting the L.
5:13
Now I should be able to delete these
two calls to the executeUpdate method.
5:19
Let's compile and run our code to
see if we get the same results.
5:25
javac JdbcMain.java.
5:30
Looks like all compiles well.
5:34
So, let's run it specifying the class
path that includes both the jar file and
5:36
the current directory.
5:41
Awesome!
5:46
Same result as before.
5:47
We've now abstracted away the actual
SQL for insert statements.
5:49
So up above, instead of crafting
the actual SQL statements,
5:53
we can simply call our save method and
it takes care of the details for us.
5:57
Hey, great job!
6:03
You've now used Java to connect to and
interact with a database.
6:05
In addition, you've taken your first step
toward allowing the saving of POJOs.
6:09
It's nice to be able to call a save method
with your POJO instead of having to craft
6:14
and re-craft SQL statements
with every database change.
6:18
You're well on your way to discovering
the next level of data management
6:22
using application code.
6:25
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