Showing posts with label JDBC. Show all posts
Showing posts with label JDBC. Show all posts

Calling a Stored Function from JDBC

The code we should write to call a stored procedure or function via JDBC is slightly different from the one we write to perform a SQL SELECT. A CallableStatement is used instead of a Statement plus a ResultSet to set the parameter, execute the call, and extract the result.

To check it, I have firstly created a stored function in my Oracle 12 instance, on the HR schema. It takes a SQL CHAR in input, and returns the same string with 'suffix' appended:
create or replace FUNCTION foo (val CHAR)
    RETURN val || 'suffix';
I ensured it works as I expected running this query:
SELECT foo('hello') FROM DUAL;
The I have written a couple of tests to see how to get the same result in Java. Not just one, because we can use either the JDBC escape and the PL/SQL block syntax to achieve the same result, being the first
{? = call foo(?)
and the latter
begin ? := foo(?); end;
The core of both tests is in these few lines:
cs = conn.prepareCall(call);  // 1
cs.registerOutParameter(1, Types.CHAR);  // 2
cs.setString(2, "aa");
String result = cs.getString(1);  // 3
1. Assuming conn is a good java.sql connection to the HR user on my Oracle database, and call is either the JDBC escape or the PL/SQL block string showed above, the prepareCall() should return a good CallableStatement.
2. The callable statement has to know the type of the output parameter is a character string. Then we set the other parameter, with the string that we want to pass as input.
3. After executing the callable statement, we get the first (and only) result as a string.

The actual code, that you could find on GitHub, class GettingStartedTest methods callFoo(), testFunctionCallJdbcEscape(), and testFunctionCallPlSqlBlock(), is a bit more verbose because I have to provide all the standard boilerplate, initializing, testing, cleaning up.

Reference: Oracle Database JDBC Developer's Guide 12c Release 2 (12.2) 2.8 Stored Procedure Calls in JDBC Programs

Go to the full post

Selecting on Oracle via JDBC

Once we decided how to establish a connection to the database, performing a SELECT on it is pretty simple. Here I'm going to use OracleDataSource as connection provider, using pure JDBC doesn't add any complexity.

The only problem in this Java code is that is slightly boring. So boring that there are a few wrapper aiming at keeping the advantages of JDBC easing its usage. See for instance the Spring JdbcTemplate.

Anyway, firstly we open a connection, then a statement, on which we execute a query (a select, in this case) that return a resultset. We normally do something on the resultset, and then we can close what we have opened, in reversed order, resultset, statement, connection. The code is made even more boring by the need of try-catching the SQLExceptions that could be thrown. Last straw in this boredom parade, is that before closing the JDBC objects we have to ensure they have been created, checking them for not being null.

So, our typical plain JDBC code could be seen in three steps:


// ...
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
try {
    conn = ods.getConnection();  // 1
    stmt = conn.createStatement();
    rs = stmt.executeQuery("SELECT first_name FROM employees");  // 2

    // ...
1. I'm using the OracleDataSourceConnector I described in the previous post. Nothing fancy, anyway, I simply get a connection to a Oracle database for the well known hr example user.
2. Having extracted a statement from the connection, I execute a query, that is plain SQL SELECT. The resulting table, here consisting of just one column, is returned in a ResultSet.


Let's do something with the fetched data. Here I copy the first names to a list of string, then I sort them and I ensure the first and last are what I expect. Usually this part of the job has more sense.
List<String> results = new ArrayList<String>();
while ( {

assertEquals(107, results.size());
assertEquals("Adam", results.get(0));
assertEquals("Winston", results.get(106));
The employees table on HR should have 107 rows, first names should range from Adam to Winston, however, your result may vary.


Finally (actually, the code is normally performed in the finally block following the try one where the initialization and operation happened - meaning that we would always perform this step, whatever happens there), being done with the data, we can close result set, statement, and connection.


Notice that we have to strictly follow the inverted order seen in initialization.
Notice also that each close() method could throw and exception so, again, these calls have to be in a try-catch block.

See full code on GitHub, class GettingStartedTest, method testSelect().

Reference: Oracle Database JDBC Developer's Guide 12c Release 2 (12.2) 2.4 Sample: Connecting, Querying, and Processing the Results

Go to the full post

Connecting to Oracle via JDBC

There are a couple of ways to connect to a recent Oracle Database, going through the standard DriverManager class or the specific OracleDataSource one. Let's see both of them. And, when we are there, let's add also some consideration on connecting to MySql via DriverManager.

It's a bit of an overkill, but I have written a little abstract class that is going to be the root of a hierarchy of classes for providing access to database through JDBC:
public abstract class Connector {
    public abstract Connection getConnection() throws SQLException;
    public String getDatabaseVersion(Connection conn) throws SQLException {
        return conn.getMetaData().getDatabaseProductVersion();
The point of it is that each different concrete class has its own way to get a database connection but all of them would use it in the same way. So the getConnection() method is abstract where the actual method performing JDBC operation, like getDatabaseVersion(), would act in the same way.

Using OracleDataSource

The OracleDataSourceConnector extends Connector, and its raison d'être is keeping an instance of a OracleDataSource object as its private data member. Initialized in the constructor, is used by the the getConnection() method to return a database connection.
public class OracleDataSourceConnector extends Connector {
    private OracleDataSource ods;

    public OracleDataSourceConnector(String url, String user, String password) throws SQLException {
        ods = new OracleDataSource();

    public Connection getConnection() throws SQLException {
        return ods.getConnection();
The good thing about OracleDataSource is that it has its own pool of connections that is managed implicitly. On the flip side, it is not standard JDBC. That means extra work if we want to adapt our code to use a different database.

I have written a tester to check the functionality, OracleDataSourceConnectorTest. See it on GitHub for full reference. There are only a few things that I want to stress here.
public class OracleDataSourceConnectorTest {
    private static final String URL = "jdbc:oracle:thin:@localhost:1521/orclpdb";  // 1
    private static final String USER = "hr";
    private static final String PASSWORD = "hr";

    private static OracleDataSourceConnector ods;
    private static Connection conn;

    public static void setUp() {  // 2
        try {
            ods = new OracleDataSourceConnector(URL, USER, PASSWORD);
            conn = ods.getConnection();
        } catch (SQLException e) {

    // ...
1. I'm using the thin Oracle JDBC driver, the other choice is the OCI one. See the Oracle documentation if you wonder which one to use. Short answer is, usually thin is the one you want to peek. My database is local, on the standard port, and the service is named orclpdb. Your setup may vary.
2. I setup the connector and a connection through this static method called only once before the tests in the class are called. The sense is that I don't want to repeat expensive operations without a reason. So, when nothing is against it, I would reuse connector and connection in more tests.

And here is a test that requires its own connector, because I want to perform a disruptive negative test:
public void testBadUser() {
 OracleDataSourceConnector connector = null;
 try {
  connector = new OracleDataSourceConnector(URL, "Unknown", PASSWORD);  // 1
 } catch (SQLException e) {
 try {
  connector.getConnection();  // 2
  fail("No connection expected for unknown user");
 } catch (SQLException e) {
  String expectedState = "72000";
  assertEquals(expectedState, e.getSQLState());
  int expectedCode = 1017;
  assertEquals(expectedCode, e.getErrorCode());
1. I pass a bas user name to the connector. No failure is expected here, since no connection is actually done.
2. I expect the failure to happen here. Oracle should react with a ORA-01017 error code, that is included in the SQL state 72000, SQL execute phase errors.

The other test ensures that I can actually get to the database:
public void testGetDatabaseNameVersion() {
 try {
  String expected = "Oracle Database 12c Enterprise Edition Release - 64bit Production";
  String actual = ods.getDatabaseVersion(conn);
  assertEquals(expected, actual);
 } catch (SQLException e) {
Using DriverManager

If I am not interested in the connection pooling service offered by OracleDataSource, and I prefer to keep as generic as I can, I could use these other solution. In the old days, it required to perform an explicit registration of the JDBC driver:
Where klass is the actual class name, like "oracle.jdbc.driver.OracleDriver" or "com.mysql.jdbc.Driver".

Now this is done implicitly by the DriverManager, that leads to a very slim connector:
public class PlainConnector extends Connector {
 private String url;
 private String user;
 private String password;

 public PlainConnector(String url, String user, String password) {
  this.url = url;
  this.user = user;
  this.password = password;

 public Connection getConnection() throws SQLException {
  return DriverManager.getConnection(url, user, password);
The constructor just store a copy of the data for connecting to the database, the getConnection() uses them going through DriverManager.

I have written another test case to see that actually the plain connector works as the OracleDataSource one. An then another one to see what I have to change to access with the same class a different database, here MySql.

This test case is accessing a MySql database that I have installed locally and on which I have added a user named "hr", to keep it close to the Oracle one. You can see how minimal are the required changes.

I had to change the URL:
private static final String URL = "jdbc:mysql://localhost:3306/hr?useSSL=false";
Notice the parameter useSLL set to false, to remove the MySql warning "Establishing SSL connection without server's identity verification is not recommended." In this test we can live without id verification.

In case of bad user, I expect now 28000 as SQL state and 1045, access denied, as error code.

And, the database version now should be something like "5.7.19-log"

Ah, right. Remember to put in your application build path the jar for oracle JDBC (currently named ojdbc8.jar) and for MySql (mysql-connector-java-5.1.43-bin.jar) and to have the databases up and running, if you want your tests to succeed.

Reference: Oracle Database JDBC Developer's Guide 12c Release 2

Full Java code on GitHub.

Go to the full post

Using JdbcTemplate in Spitter Web App

In the previous post I developed a CommandLineRunner Spring App to show how to use JdbcTemplate for simplify the JDBC access to an embedded instance of a H2 database. Here I port the changes to the Spittr Web App I have built up previously.

Actually, there is not much to say. There is some inconsistency between the two apps that spiced up the process, but nothing really complicated. I'd say the most interesting part is in the POM file. Here I removed, whenever it was possible, the versioning for each single dependency, relying instead on the parent element, where they are defined.
    <relativePath />
However, for some reason, Spring could not find the version for the JSP dependency, so I kept it as before
And left the versioning for it among the properties.
I pushed the new version of Spittr on GitHub.

Go to the full post

Spring and JdbcTemplate

Let's say that we want to write a Spring application that requires some simple database activity. We decide to use an embedded database, H2 and, instead of choosing a higher level persistency framework, we decide to go for the JDBC support, mediating it with JdbcTemplate, a Spring class aimed at simplifying its use.

I create a Spring project using the STS wizard (File >> New >> Spring Starter Project).
Since I want to use JDBC and the H2 database support, I select these two options from the dependencies page:
From database schema to POJOs

In the source/main/resources folder, I put a file named schema.sql, this is enough for Spring, that knows it has to get it and run it at startup, so there I put the SQL commands to create my tables. I create two tables, spitter and spittle, connected by the id of the first, that is a foreign key in the second.

The tables defined in the database are reflected in a couple of plain old Java classes, and, having as fields what in the tables are the columns.

There is one thing that I think is interesting. The SQL spittle table has, among the other fields, a datetime, postedTime. We need to find a counterpart for it in the Java world. Since we are not interested here in time zones and the such, just in a plain timestamp, I decided to use Java 8 java.time.Instant.

That's it. If the SQL stuff is simple, and I have just a couple of tables, I could give it for done. To see that, I have created a basic version for the SpringBootApplication that implements the CommandLineRunner interface:
public class UsingJdbcApplication implements CommandLineRunner {
    private static final Logger log = LoggerFactory.getLogger(UsingJdbcApplication.class);

    private JdbcTemplate template;  // 1

    public static void main(String[] args) {, args);

    public void run(String... args) throws Exception {
        Long counter = template.queryForObject("SELECT count(id) FROM spitter", Long.class);  // 2"Rows on spitter table: " + counter);"Pushing a spitter in");
        Object[] admin = new Object[] { "admin", "password", "Admin", "admin@example.dd" };
        template.update("INSERT INTO spitter(username, password, fullname, email) VALUES(?, ?, ?, ?)", admin);  // 3

        template.query("SELECT * FROM spitter WHERE username = ?", new Object[] { "admin" },  // 4
                (rs, rowNum) -> new Spitter(rs.getLong("id"), rs.getString("username"), rs.getString("password"),
                        rs.getString("fullname"), rs.getString("email"), rs.getBoolean("updateByEmail")))
                .forEach(spitter ->"Spitter: " + spitter.toString()));
1. Sort of magic. We ask to Spring to wire this JdbcTemplate object. Since the H2 jar is in the classpath, it understands it has to use it as database. We don't provide any settings, and it uses a whole bunch of defaults. Usually not a good idea for production code, but very handy for prototyping.
2. Let's run a simple query that returns a single value. This line shows that actually Spring has initialized the database using the script named schema.sql that it found in the main resources folder. And how JdbcTemplate makes our life so much simpler. Notice that the queryForObject() method has a first parameter that is the SQL statement we want to run, and the second one that is the type for the expected return value.
3. A parametrized update(). Its first parameter is a parametrized JDBC SQL insert statement, the second one a vector of objects containing the values that we want to usein the query.
4. Something a bit more complicated. The query() method execute a query in a way similar to the update() seen above but, as third parameter, it accepts a lambda function that maps each row in the resulting resultset to a new Spitter object. We tipically have no use for the rowNum parameter, just access any resultset field we need.
This query() call returns a list of Spitter. On that list we apply a forEach() so that each element in the list is logged. Actually, here we are expecting just one Spitter, however this is a common pattern that we should learn to recognize and use.

Running the Spring Boot App, I can see in the console window the expected log.

Repositories and configuration

Usually we don't want to scatter SQL statements all over our Java code. So we create two interfaces, one for Spittle and one for Spitter, that act as repository for them, and then we implement them for our JDBC provider.
The two classes are quite similar. Let's see some parts of JdbcSpittleRepository, that is a tad more complicated.
// ...
private static final String SELECT = "select, as spitterId, s.username, s.password, s.fullname,, s.updateByEmail, sp.message, sp.postedTime from Spittle sp, Spitter s where sp.spitter =";
private static final String SELECT_RECENT = SELECT + " order by sp.postedTime desc limit ?";

public List<Spittle> findRecent(int count) {
    return template.query(SELECT_RECENT, new SpittleRowMapper(), count);  // 1

// ...
private long insertSpittle(Spittle spittle) {
    SimpleJdbcInsert insert = new SimpleJdbcInsert(template).withTableName("Spittle");  // 2
    Map<String, Object> args = new HashMap<String, Object>();
    args.put("spitter", spittle.getSpitter().getId());
    args.put("message", spittle.getMessage());
    args.put("postedTime", Timestamp.from(spittle.getPostedTime()));
    long spittleId = insert.executeAndReturnKey(args).longValue();
    return spittleId;

// ...
private static final class SpittleRowMapper implements RowMapper<Spittle> {  // 3
    public Spittle mapRow(ResultSet rs, int rowNum) throws SQLException {
        long id = rs.getLong("id");
        String message = rs.getString("message");
        Instant postedTime = rs.getTimestamp("postedTime").toInstant();
        long spitterId = rs.getLong("spitterId");
        String username = rs.getString("username");
        String password = rs.getString("password");
        String fullName = rs.getString("fullname");
        String email = rs.getString("email");
        boolean updateByEmail = rs.getBoolean("updateByEmail");
        Spitter spitter = new Spitter(spitterId, username, password, fullName, email, updateByEmail);
        return new Spittle(id, spitter, message, postedTime);
1. Almost an innocent JdbcTemplate wrapper to a JDBC query, if we don't pay much attention to the second parameter, that would convert the ResultSet coming from the SQL select in a list of Spittles. See the SpittleRowMapper below for details.
2. Here we see how SimpleJdbcInsert helps us in writing readable code when we want to insert a row in a table, in the case where the database will take the burden of generating a key for us, and we need to return it to the caller. After specifying the table we are working on, we set the name of the field that is a generated key, and then, as a map, the field names and associated values. Finally we have just to pass them to the SimpleJdbcInsert by executeAndReturnKey().
3. The SpittleRowMapper seen in action in (1). Its mapRow() method maps a single row from the underneath table in a Spittle object.

In some way, Spring has to configure these repositories, passing to them a viable JdbcTemplate object. In this app, it is done by JdbcConfig, annotated as a Spring Configuration class. It generates a few beans (in the Spring sense of the term) representing the DataSource, JdbcTemplate, the repositories, and also a transaction manager. We'll see them at work in the tester. It interesting seeing how the DataSource is set, when we don't rely on the default initialization by Spring.
public class JdbcConfig {
    public DataSource dataSource() {
        return new EmbeddedDatabaseBuilder()
                .addScripts("schema.sql", "test-data.sql")
    // ...
This data source represents an embedded database, H2 type, that would run a couple of scripts at startup. We already seen the first one, schema.sql, here I added a second one, that contains a bunch of SQL insert for spitters and spittles rows.


There are a couple of JUnit test, one for Spitter the other one for Spittle repository. They are quite similar. Let's have a fast look at first one.
@ContextConfiguration(classes = JdbcConfig.class)  // 1
public class JdbcSpitterRepositoryTest {
    JdbcSpitterRepository spitterRepository;  // 2

    // ...
    @Transactional  // 3
    public void findAll() {
        List<Spitter> spitters = spitterRepository.findAll();  // 4
        assertEquals(4, spitters.size());
        assertSpitter(0, spitters.get(0));
        assertSpitter(1, spitters.get(1));
        assertSpitter(2, spitters.get(2));
        assertSpitter(3, spitters.get(3));

1. Here I'm saying to Spring to fetch the JdbcConfig class and use it to configure itself for testing.
2. Thanks to (1) we can ask to Spring to autowire the spitter repository.
3. Having defined a PlatformTransactionManager, we can use it to keep very simple the transaction management. A transaction is started and completed, eventually rolled-back, behind the curtains.
4. The spitters come from the test-data.sql called at startup by JdbcConfig dataSource().

Reference: Hitting the database with Spring and JDBC, from Spring in Action, Fourth Edition by Craig Walls, chapter ten.

This complete Spring application is on GitHub.

Go to the full post