{* ../../docs_src/handling_errors/tutorial002.py hl[14] *}

## Install custom exception handlers { #install-custom-exception-handlers }

You can add custom exception handlers with <a href="https://www.starlette.io/exceptions/" class="external-link" target="_blank">the same exception utilities from Starlette</a>.

Let's say you have a custom exception `UnicornException` that you (or a library you use) might `raise`.

/**
 * Base class for all maven exceptions carrying {@link BuilderProblem}s.
 *
 * @since 4.0.0
 */
@Experimental
public abstract class MavenBuilderException extends MavenException {

    /**
     * The collection of problems associated with this exception.
     */
    private final ProblemCollector<BuilderProblem> problems;

    /**
     * Constructs a new exception with the specified message and cause.

                        throw new IOException("Interrupted during retry delay", e);
                    }
                }
            }
        }

        // All retries failed
        if (lastError instanceof IOException) {
            throw (IOException) lastError;
        } else {
            throw new IOException("RDMA operation failed after " + (retryCount + 1) + " attempts", lastError);

    void testExceptionHierarchy() {
        // When
        RuntimeCIFSException exception = new RuntimeCIFSException("Test");

        // Then
        assertTrue(exception instanceof RuntimeException);
        assertTrue(exception instanceof Exception);
        assertTrue(exception instanceof Throwable);
    }

    @Test
    @DisplayName("Should support exception chaining")

        // This test verifies that attempting to open a connection for an unsupported protocol
        // results in an IOException, as no default handler should be found.
        assertThrows(IOException.class, () -> {
            handler.openConnection(new URL("unknownprotocol://somehost/path"));
        }, "Should throw IOException for an unknown protocol.");
    }

    @Test
    void testSetURLStreamHandlerFactory_SuccessFirstTime() {

    @DisplayName("Parse rejects wrong SPNEGO OID")
    void testParseRejectsWrongOid() throws Exception {
        byte[] token = buildInitToken(new ASN1ObjectIdentifier[] { OID_KRB }, 0, null, null, false, "1.2.840.113554.1.2.2", // Kerberos OID instead of SPNEGO OID
                null, null);

        IOException ex = assertThrows(IOException.class, () -> new NegTokenInit(token));

    void mockInteraction_stubsThrow_andVerifiesInvocation() {
        // Arrange: Since SmbUnsupportedOperationException is a checked exception (extends IOException),
        // we need to use a method that can throw checked exceptions or wrap it in a RuntimeException
        @SuppressWarnings("unchecked")
        Supplier<String> supplier = mock(Supplier.class);

        // Both transports fail
        SmbTransportImpl trans1 = mock(SmbTransportImpl.class);
        SmbTransportImpl trans2 = mock(SmbTransportImpl.class);

        IOException firstException = new IOException("First failure");
        IOException secondException = new IOException("Second failure");

        when(trans1.unwrap(SmbTransportImpl.class)).thenReturn(trans1);
        when(trans1.ensureConnected()).thenThrow(firstException);

        assertNotNull(exception);
        assertEquals(SmbOperationException.ErrorCode.FILE_NOT_FOUND, exception.getErrorCode());
        assertTrue(exception.getMessage().contains("FILE_NOT_FOUND"));
        assertTrue(exception.getMessage().contains("test.txt"));
        assertEquals(SmbOperationException.ErrorCategory.FILE_SYSTEM, exception.getErrorCategory());
        assertFalse(exception.isRetryable());
    }

    @Test

        validator = new ServerResponseValidator();
    }

    @Test
    public void testValidBuffer() throws Exception {
        byte[] buffer = new byte[1024];
        validator.validateBuffer(buffer, 100, 2048);
        // Should pass without exception
    }

    @Test
    public void testNullBuffer() throws Exception {
        assertThrows(SmbException.class, () -> {
            validator.validateBuffer(null, 100, 1024);