如何从不可变对象创建实例？

Question

我正在尝试从不可变对象创建一个新实例。在这种情况下，是一个列表，我收到此错误：

java.lang.InstantiationException: java.util.Collections$UnmodifiableRandomAccessList
    at java.lang.Class.newInstance(Class.java:364)
    at com.example.movies.domain.transformer.DomainEntityTransformer.transformEntityArray(DomainEntityTransformer.java:32)
    at com.example.movies.domain.service.client.impl.ClientServiceImpl.getClients(ClientServiceImpl.java:58)
    at com.example.movies.service.controller.ClientController.getClients(ClientController.java:50)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:137)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:777)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:706)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:943)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:877)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:857)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:618)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:516)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1086)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:659)
    at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:223)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1558)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1515)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)

这是抛出异常的转换器class

public Collection<DOM> transformEntityArray(Collection<ENT> iterable) {
    try {
        Collection<DOM> transformed = iterable.getClass().newInstance();
        Iterator<ENT> iterator = iterable.iterator();
        while (iterator.hasNext()) {
            ENT element = iterator.next();
            transformed.add(this.transformEntity(element));
        }
        return transformed;
    } catch (Exception e) {
        e.printStackTrace();
        return null;
    }
}

这是实现

Page<Client> clientsEntity = this.dao.findAll(new PageRequest(offset, limit));
List<ClientDomain> clientsDomain = (List<ClientDomain>) this.transformer.transformEntityArray(clientsEntity
    .getContent());

你知道人们如何修复它吗？问候！

Answer 1

是的，我们

transformed = new ArrayList<>();

通常（即使在您的情况下没有任何意义），您可以通过使用所有必要的参数调用适当的构造函数来设置对象的状态来创建不可变对象。

你的情况是 UnmodifiableRandomAccessList(List<? extends E> list), 您可以通过 getClass().getConstructor... 访问（您仍然需要临时 ArrayList 来存储您的结果）。

但是您不能提供适用于任何输入集合的通用解决方案，因为您需要知道要调用哪个构造函数 == 知道实际调用参数的 java 代码。这使得使用 Genereirc 和接口完全没有意义。

因此只需创建任意选择的集合 (ArrayList)，因为它不会影响代码的其他部分。

如何从不可变对象创建实例？

how to create instance from an inmutable objects?

java

immutability

instantiation