I am using Spring Boot and Spring Data Elastic. I have an accounts index data like below

public interface AccountsRepository extends ElasticsearchRepository<Accounts, Long> {
    
    List<Accounts> findByLastname(String lastname);
    
    List<Accounts> findByAge(Integer age);
}

I am getting below error when perform findAll(). How to fix the below issue?
@Service
public class AccountsService {
    @Autowired
    private AccountsRepository repository;

    public List<Accounts> findAllAccounts(){
        return (List<Accounts>) repository.findAll();
    }
}

Model
@Data
@AllArgsConstructor
@NoArgsConstructor
@Document(indexName = "accounts", createIndex = false)
public class Accounts {
    @Id
    private Long account_number;
    private Long balance;
    private String firstname;
    private String lastname;
    private Integer age;
    private String gender;
    private String address;
    private String employer;
    private String email;
    private String city;
    private String state;
}

Error:
2023-06-02 21:23:23.784  WARN 44796 --- [nio-8080-exec-1] org.elasticsearch.client.RestClient      : request [POST http://localhost:9200/accounts/_search?typed_keys=true&max_concurrent_shard_requests=5&search_type=query_then_fetch&batched_reduce_size=512] returned 1 warnings: [299 Elasticsearch-7.15.0-79d65f6e357953a5b3cbcc5e2c7c21073d89aa29 "Elasticsearch built-in security features are not enabled. Without authentication, your cluster could be accessible to anyone. See https://www.elastic.co/guide/en/elasticsearch/reference/7.15/security-minimal-setup.html to enable security."]
2023-06-02 21:23:23.878  WARN 44796 --- [nio-8080-exec-1] org.elasticsearch.client.RestClient      : request [POST http://localhost:9200/accounts/_search?typed_keys=true&max_concurrent_shard_requests=5&search_type=query_then_fetch&batched_reduce_size=512] returned 1 warnings: [299 Elasticsearch-7.15.0-79d65f6e357953a5b3cbcc5e2c7c21073d89aa29 "Elasticsearch built-in security features are not enabled. Without authentication, your cluster could be accessible to anyone. See https://www.elastic.co/guide/en/elasticsearch/reference/7.15/security-minimal-setup.html to enable security."]
2023-06-02 21:23:24.170 ERROR 44796 --- [nio-8080-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.core.convert.ConversionFailedException: Failed to convert from type [java.lang.String] to type [java.lang.Long] for value 'KH-9fIgBhfTLJt8QzMP_'; nested exception is java.lang.NumberFormatException: For input string: "KH-9fIgBhfTLJt8QzMP_"] with root cause

java.lang.NumberFormatException: For input string: "KH-9fIgBhfTLJt8QzMP_"
    at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:65) ~[na:na]
    at java.base/java.lang.Long.parseLong(Long.java:692) ~[na:na]
    at java.base/java.lang.Long.valueOf(Long.java:1144) ~[na:na]
    at org.springframework.util.NumberUtils.parseNumber(NumberUtils.java:214) ~[spring-core-5.3.21.jar:5.3.21]
    at org.springframework.core.convert.support.StringToNumberConverterFactory$StringToNumber.convert(StringToNumberConverterFactory.java:64) ~[spring-core-5.3.21.jar:5.3.21]
    at org.springframework.core.convert.support.StringToNumberConverterFactory$StringToNumber.convert(StringToNumberConverterFactory.java:50) ~[spring-core-5.3.21.jar:5.3.21]
    at org.springframework.core.convert.support.GenericConversionService$ConverterFactoryAdapter.convert(GenericConversionService.java:437) ~[spring-core-5.3.21.jar:5.3.21]
    at org.springframework.core.convert.support.ConversionUtils.invokeConverter(ConversionUtils.java:41) ~[spring-core-5.3.21.jar:5.3.21]
    at org.springframework.core.convert.support.GenericConversionService.convert(GenericConversionService.java:192) ~[spring-core-5.3.21.jar:5.3.21]
    at org.springframework.core.convert.support.GenericConversionService.convert(GenericConversionService.java:175) ~[spring-core-5.3.21.jar:5.3.21]
    at org.springframework.data.elasticsearch.core.convert.MappingElasticsearchConverter$Reader.getPotentiallyConvertedSimpleRead(MappingElasticsearchConverter.java:562) ~[spring-data-elasticsearch-4.4.1.jar:4.4.1]
    at org.springframework.data.elasticsearch.core.convert.MappingElasticsearchConverter$Reader.readValue(MappingElasticsearchConverter.java:460) ~[spring-data-elasticsearch-4.4.1.jar:4.4.1]
    at org.springframework.data.elasticsearch.core.convert.MappingElasticsearchConverter$Reader.readValue(MappingElasticsearchConverter.java:442) ~[spring-data-elasticsearch-4.4.1.jar:4.4.1]
    at org.springframework.data.elasticsearch.core.convert.MappingElasticsearchConverter$Reader$ElasticsearchPropertyValueProvider.getPropertyValue(MappingElasticsearchConverter.java:621) ~[spring-data-elasticsearch-4.4.1.jar:4.4.1]
    at org.springframework.data.elasticsearch.core.convert.MappingElasticsearchConverter$Reader.readProperties(MappingElasticsearchConverter.java:404) ~[spring-data-elasticsearch-4.4.1.jar:4.4.1]
    at org.springframework.data.elasticsearch.core.convert.MappingElasticsearchConverter$Reader.readEntity(MappingElasticsearchConverter.java:327) ~[spring-data-elasticsearch-4.4.1.jar:4.4.1]
    at org.springframework.data.elasticsearch.core.convert.MappingElasticsearchConverter$Reader.read(MappingElasticsearchConverter.java:258) ~[spring-data-elasticsearch-4.4.1.jar:4.4.1]
    at org.springframework.data.elasticsearch.core.convert.MappingElasticsearchConverter$Reader.read(MappingElasticsearchConverter.java:217) ~[spring-data-elasticsearch-4.4.1.jar:4.4.1]
    at org.springframework.data.elasticsearch.core.convert.MappingElasticsearchConverter.read(MappingElasticsearchConverter.java:161) ~[spring-data-elasticsearch-4.4.1.jar:4.4.1]
    at org.springframework.data.elasticsearch.core.convert.MappingElasticsearchConverter.read(MappingElasticsearchConverter.java:83) ~[spring-data-elasticsearch-4.4.1.jar:4.4.1]
    at org.springframework.data.elasticsearch.core.AbstractElasticsearchTemplate$ReadDocumentCallback.doWith(AbstractElasticsearchTemplate.java:745) ~[spring-data-elasticsearch-4.4.1.jar:4.4.1]
    at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:195) ~[na:na]
    at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1655) ~[na:na]
    at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484) ~[na:na]
    at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474) ~[na:na]
    at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913) ~[na:na]
    at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[na:na]
    at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578) ~[na:na]
    at org.springframework.data.elasticsearch.core.AbstractElasticsearchTemplate$ReadSearchDocumentResponseCallback.doWith(AbstractElasticsearchTemplate.java:778) ~[spring-data-elasticsearch-4.4.1.jar:4.4.1]
    at org.springframework.data.elasticsearch.core.AbstractElasticsearchTemplate$ReadSearchDocumentResponseCallback.doWith(AbstractElasticsearchTemplate.java:763) ~[spring-data-elasticsearch-4.4.1.jar:4.4.1]
    at org.springframework.data.elasticsearch.core.ElasticsearchRestTemplate.search(ElasticsearchRestTemplate.java:404) ~[spring-data-elasticsearch-4.4.1.jar:4.4.1]
    at org.springframework.data.elasticsearch.repository.support.SimpleElasticsearchRepository.lambda$findAll$1(SimpleElasticsearchRepository.java:123) ~[spring-data-elasticsearch-4.4.1.jar:4.4.1]
    at org.springframework.data.elasticsearch.repository.support.SimpleElasticsearchRepository.execute(SimpleElasticsearchRepository.java:355) ~[spring-data-elasticsearch-4.4.1.jar:4.4.1]
    at org.springframework.data.elasticsearch.repository.support.SimpleElasticsearchRepository.findAll(SimpleElasticsearchRepository.java:123) ~[spring-data-elasticsearch-4.4.1.jar:4.4.1]
    at org.springframework.data.elasticsearch.repository.support.SimpleElasticsearchRepository.findAll(SimpleElasticsearchRepository.java:112) ~[spring-data-elasticsearch-4.4.1.jar:4.4.1]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
    at org.springframework.data.repository.core.support.RepositoryMethodInvoker$RepositoryFragmentMethodInvoker.lambda$new$0(RepositoryMethodInvoker.java:289) ~[spring-data-commons-2.7.1.jar:2.7.1]
    at org.springframework.data.repository.core.support.RepositoryMethodInvoker.doInvoke(RepositoryMethodInvoker.java:137) ~[spring-data-commons-2.7.1.jar:2.7.1]
    at org.springframework.data.repository.core.support.RepositoryMethodInvoker.invoke(RepositoryMethodInvoker.java:121) ~[spring-data-commons-2.7.1.jar:2.7.1]
    at org.springframework.data.repository.core.support.RepositoryComposition$RepositoryFragments.invoke(RepositoryComposition.java:530) ~[spring-data-commons-2.7.1.jar:2.7.1]
    at org.springframework.data.repository.core.support.RepositoryComposition.invoke(RepositoryComposition.java:286) ~[spring-data-commons-2.7.1.jar:2.7.1]
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$ImplementationMethodExecutionInterceptor.invoke(RepositoryFactorySupport.java:640) ~[spring-data-commons-2.7.1.jar:2.7.1]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.21.jar:5.3.21]
    at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.doInvoke(QueryExecutorMethodInterceptor.java:164) ~[spring-data-commons-2.7.1.jar:2.7.1]
    at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.invoke(QueryExecutorMethodInterceptor.java:139) ~[spring-data-commons-2.7.1.jar:2.7.1]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.21.jar:5.3.21]
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:97) ~[spring-aop-5.3.21.jar:5.3.21]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.21.jar:5.3.21]
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:215) ~[spring-aop-5.3.21.jar:5.3.21]
    at com.sun.proxy.$Proxy59.findAll(Unknown Source) ~[na:na]
    at com.example.service.AccountsService.findAllAccounts(AccountsService.java:16) ~[classes/:na]
    at com.example.controller.AccountsController.findAllAccounts(AccountsController.java:19) ~[classes/:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205) ~[spring-web-5.3.21.jar:5.3.21]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:150) ~[spring-web-5.3.21.jar:5.3.21]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:117) ~[spring-webmvc-5.3.21.jar:5.3.21]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.3.21.jar:5.3.21]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808) ~[spring-webmvc-5.3.21.jar:5.3.21]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.3.21.jar:5.3.21]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1067) ~[spring-webmvc-5.3.21.jar:5.3.21]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963) ~[spring-webmvc-5.3.21.jar:5.3.21]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.3.21.jar:5.3.21]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.3.21.jar:5.3.21]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:655) ~[tomcat-embed-core-9.0.64.jar:4.0.FR]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.3.21.jar:5.3.21]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:764) ~[tomcat-embed-core-9.0.64.jar:4.0.FR]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.64.jar:9.0.64]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.21.jar:5.3.21]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.21.jar:5.3.21]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.21.jar:5.3.21]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.21.jar:5.3.21]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.21.jar:5.3.21]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.21.jar:5.3.21]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:360) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:890) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1787) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.64.jar:9.0.64]
    at java.base/java.lang.Thread.run(Thread.java:834) ~[na:na]


How to only get _source fields of elasticsearch using Spring Data Elastic?
You marked the property account_number of your entity, which is a Long, as the @Id. But the id in your index is a String (here with the value "KH-9fIgBhfTLJt8QzMP_").
Add proper id property:
@Id
private String id;

Edit: 03.06.2023:
As for the error

java.lang.ClassCastException: class org.springframework.data.domain.PageImpl cannot be cast to class java.util.List (org.springframework.data.domain.PageImpl

findAll() is defined to return an Iterable, which is an interface. The actual returned objects is of type PageImpl which implements Page which extends Iterable.
You cannot cast a Page implementation to a List<Accounts>.
