1

我正在使用 Java 8 开发 Spring Boot 版本 2，当我尝试在“createTopic”方法中将新的 List 对象添加到预定义的 List 对象（即 topicList）时出现错误。

**

主题服务.java

**

public class TopicService {

    private List<TopicObject>  topicList = Arrays.asList(
            new TopicObject("Java", "Java Course", "Spring boot in java"),
            new TopicObject("Maths", "Mathematics class","12th maths")
    );



    public String createTopic(TopicObject topicObj){

         topicList.add(new TopicObject("Java1", "Java Course1", "Spring boot in java1"));

        return "Request successful"  ;
    }
}

**

主题对象.java

**

package io.javabrains.springBootStarter.controller;

import com.fasterxml.jackson.annotation.JsonProperty;

public class TopicObject {

    @JsonProperty("id")
    private String id;

    @JsonProperty("name")
    private String name;

    @JsonProperty("description")
    private String description;

    public TopicObject() {
    }

    public TopicObject(String id, String name, String description) {
        this.id = id;
        this.name = name;
        this.description = description;
    }


    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

}

**

错误

**

2020-04-15 19:52:27.172 错误 15312 --- [nio-8080-exec-2] oaccC[.[.[/].[dispatcherServlet]：Servlet.service() 用于 servlet [dispatcherServlet] path [] 抛出异常 [请求处理失败；嵌套异常是 java.lang.UnsupportedOperationException] 的根本原因

java.lang.UnsupportedOperationException: null at java.util.AbstractList.add(AbstractList.java:148) ~[na:1.8.0_221] at java.util.AbstractList.add(AbstractList.java:108) ~[na:1.8 .0_221] 在 io.javabrains.springBootStarter.Service.TopicService.createTopic(TopicService.java:29) ~[classes/:na] 在 io.javabrains.springBootStarter.controller.TopicController.createTopic(TopicController.java:31) ~[ classes/:na] 在 sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_221] 在 sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_221] 在 sun .reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_221] at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_221] at org.springframework .web.method.support。InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:209) ~[spring-web-5.0.13.RELEASE.jar:5.0.13.RELEASE] at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136 ) ~[spring-web-5.0.13.RELEASE.jar:5.0.13.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102) ~[spring- webmvc-5.0.13.RELEASE.jar:5.0.13.RELEASE] 在 org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:894) ~[spring-webmvc-5.0.13 .RELEASE.jar:5.0.13.RELEASE] 在 org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:800) ~[spring-webmvc-5.0.13.RELEASE.jar:5.0.13.RELEASE] 在 org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.0.13.RELEASE.jar:5.0.13 .RELEASE] 在 org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:991) ~[spring-webmvc-5.0.13.RELEASE.jar:5.0.13.RELEASE] 在 org.springframework.web.servlet .DispatcherServlet.doService(DispatcherServlet.java:925) ~[spring-webmvc-5.0.13.RELEASE.jar:5.0.13.RELEASE] at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:981) ~[spring-webmvc-5.0.13.RELEASE.jar:5.0.13.RELEASE] at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:884) ~[spring-webmvc-5.0.13.RELEASE .jar:5.0.13.RELEASE] 在 javax.servlet.http.HttpServlet.service(HttpServlet.java:661) ~[tomcat-embed-core-8.5.39.jar:8.5.39] at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:858) ~[spring-webmvc-5.0.13 .RELEASE.jar:5.0.13.RELEASE] 在 javax.servlet.http.HttpServlet.service(HttpServlet.java:742) ~[tomcat-embed-core-8.5.39.jar:8.5.39] 在 org.apache .catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-8.5.39.jar:8.5.39] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java: 166) ~[tomcat-embed-core-8.5.39.jar:8.5.39] 在 org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) ~[tomcat-embed-websocket-8.5 .39.jar:8.5.39] 在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.39.jar:8.5.39] 在 org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.39.jar:8.5.39] 在 org.springframework.web.filter.RequestContextFilter。 doFilterInternal(RequestContextFilter.java:99) ~[spring-web-5.0.13.RELEASE.jar:5.0.13.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring -web-5.0.13.RELEASE.jar:5.0.13.RELEASE] 在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.39.jar: 8.5.39] 在 org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.39.jar:8.5.39] 在 org.springframework.web.filter。 HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:109) ~[spring-web-5.0.13.RELEASE.jar:5.0.13.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.13 .RELEASE.jar:5.0.13.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.39.jar:8.5.39] at org .apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.39.jar:8.5.39] at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter. java:93) ~[spring-web-5.0.13.RELEASE.jar:5.0.13.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0 .13.RELEASE.jar:5.0.13.RELEASE] 在 org.apache.catalina.core.ApplicationFilterChain。internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.39.jar:8.5.39] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed -core-8.5.39.jar:8.5.39] 在 org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) ~[spring-web-5.0.13.RELEASE.jar:5.0.13。 RELEASE] 在 org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.13.RELEASE.jar:5.0.13.RELEASE] 在 org.apache.catalina.core。 ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.39.jar:8.5.39] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat -embed-core-8.5.39.jar:8.5.39] 在 org.apache.catalina。core.StandardWrapperValve.invoke(StandardWrapperValve.java:199) ~[tomcat-embed-core-8.5.39.jar:8.5.39] at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [ tomcat-embed-core-8.5.39.jar:8.5.39] 在 org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:493) [tomcat-embed-core-8.5.39.jar:8.5. 39] 在 org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:137) [tomcat-embed-core-8.5.39.jar:8.5.39] 在 org.apache.catalina.valves.ErrorReportValve.invoke (ErrorReportValve.java:81) [tomcat-embed-core-8.5.39.jar:8.5.39] at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core- 8.5.39.jar:8.5.39] 在 org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343）[tomcat-embed-core-8.5.39.jar:8.5.39] 在 org.apache.coyote.http11.Http11Processor.service（Http11Processor.java:798）[tomcat-embed-core-8.5.39.jar :8.5.39] 在 org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.39.jar:8.5.39] 在 org.apache.coyote.AbstractProtocol$ConnectionHandler。进程（AbstractProtocol.java:806）[tomcat-embed-core-8.5.39.jar:8.5.39] at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun（NioEndpoint.java:1498）[tomcat -embed-core-8.5.39.jar:8.5.39] 在 org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.39.jar:8.5 .39] 在 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_221] 在 java.util.concurrent.ThreadPoolExecutor$Worker。运行（ThreadPoolExecutor.java:624）[na:1.8.0_221] 在 org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run（TaskThread.java:61）[tomcat-embed-core-8.5.39.jar :8.5.39] 在 java.lang.Thread.run(Thread.java:748) [na:1.8.0_221]

>不知道这种方式能不能把新对象加入到“topicList”中。有人可以帮忙吗？

4

2 回答 2

1

Arrays.asLit返回一个不可修改的List对象。如果您打算向其中添加元素，则需要使用可修改的List类型，例如ArrayList：

private List<TopicObject>  topicList = new ArrayList<>(Arrays.asList(
        new TopicObject("Java", "Java Course", "Spring boot in java"),
        new TopicObject("Maths", "Mathematics class", "12th maths")
));
于 2020-04-15T14:53:43.350 回答
0

Arrays.asList()不支持添加新元素。所以初始化新的 ArrayList 并添加新元素。所以而不是

private List<TopicObject>  topicList = Arrays.asList(
            new TopicObject("Java", "Java Course", "Spring boot in java"),
            new TopicObject("Maths", "Mathematics class","12th maths")
    );

改成

private List<TopicObject>  topicList = new ArrayList<>(Arrays.asList(
        new TopicObject("Java", "Java Course", "Spring boot in java"),
        new TopicObject("Maths", "Mathematics class", "12th maths")
));
于 2020-04-15T14:55:12.990 回答