* Even if empty string, treated as empty plainly. So "IF pmb != null" is false if empty.
     * @param hostname The parameter value of hostname. (NotNull)
     */
    public void setHostname(String hostname) {
        registerVariable("hostname", hostname);
    }

    /**
     * Set the value of count, used in parameter comment. <br>

                (et, vl) -> ((FileAuthentication) et).setFileConfigId(DfTypeUtil.toString(vl)), "fileConfigId");
        setupEpg(_epgMap, et -> ((FileAuthentication) et).getHostname(),
                (et, vl) -> ((FileAuthentication) et).setHostname(DfTypeUtil.toString(vl)), "hostname");
        setupEpg(_epgMap, et -> ((FileAuthentication) et).getParameters(),

                        } else {
                            postcard.addTo(fessConfig.getMailFromAddress());
                            postcard.dryrun();
                        }
                        postcard.setHostname(systemHelper.getHostname());
                        postcard.setClustername(ping.getClusterName());
                        postcard.setClusterstatus(ping.getClusterStatus());
                    });

                    } else {
                        postcard.addTo(fessConfig.getMailFromAddress());
                        postcard.dryrun();
                    }
                    postcard.setHostname(systemHelper.getHostname());
                    postcard.setLevel(level);
                    postcard.setCount(String.valueOf(levelEvents.size()));

```java
// Add OpenSearch dependency and configure
container.singleton("opensearchDataService", OpenSearchDataService.class, service -> {
    service.setIndexName("crawler-data");
    service.setHostname("localhost");
    service.setPort(9200);
});
```

## Performance Tuning

### Thread Configuration

```java
// Optimize thread pool settings

                    connector.setProperty("SSLEnabled", "true");
                    final SSLHostConfig sslHostConfig = new SSLHostConfig();
                    sslHostConfig.setHostName("_default_");
                    final SSLHostConfigCertificate certificate =
                            new SSLHostConfigCertificate(sslHostConfig, SSLHostConfigCertificate.Type.UNDEFINED);

            }

            String hostname = fessConfig.getMailHostname();
            if (StringUtil.isBlank(hostname)) {
                hostname = ComponentUtil.getSystemHelper().getHostname();
            }
            dataMap.put("hostname", hostname);

            logger.debug("\ninfoMap: {}\ndataMap: {}", infoMap, dataMap);

            when(mockInetAddress.getHostName()).thenReturn("inet-host");
            UniAddress uniAddress = new UniAddress(mockInetAddress);
            assertEquals("inet-host", uniAddress.getHostName());
        }

        @Test
        void shouldReturnNbtAddressHostnameWhenWrappedIsNbtAddress() {
            when(mockNbtAddress.getHostName()).thenReturn("nbt-host");

            @Override
            public boolean isChangedClusterState(int status) {
                // State has changed
                return true;
            }

            @Override
            public String getHostname() {
                return "test-hostname";
            }
        };

        FessConfig fessConfig = createTestFessConfig();

        // Register components

    }

    @Test
    @DisplayName("getHostName should return valid hostname or address")
    void testGetHostNameContract() {
        // Given
        String expectedHostName = "server.example.com";
        when(mockAddress.getHostName()).thenReturn(expectedHostName);

        // When
        String hostName = mockAddress.getHostName();

        // Then