我正在解析网站 html 文件中的某些元素，将它们转换为对象并将它们添加到我的数据库中，解析和创建游戏类型的对象时没有问题，我还可以根据每个游戏添加团队对象(一对一关系，因此一场比赛有一支主队和一支客队，两者都是球队类型)。 当我尝试将这些游戏/团队对象添加到数据库中现有的联赛(与游戏和团队具有一对多关系)时，我收到以下错误:(注意我正在使用 springs mvc 框架)
java.lang.NullPointerException: null
at com.FYP.Club.controller.HomeController.addNewPost(HomeController.java:98) ~[classes/:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_60]
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_60]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_60]
at java.lang.reflect.Method.invoke(Unknown Source) ~[na:1.8.0_60]
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:133) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:97) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:967) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:661) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) ~[tomcat-embed-websocket-8.5.23.jar:8.5.23]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:108) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:81) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-8.5.23.jar:8.5.23]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:478) [tomcat-embed-core-8.5.23.jar:8.5.23]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [tomcat-embed-core-8.5.23.jar:8.5.23]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) [tomcat-embed-core-8.5.23.jar:8.5.23]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.23.jar:8.5.23]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) [tomcat-embed-core-8.5.23.jar:8.5.23]
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803) [tomcat-embed-core-8.5.23.jar:8.5.23]
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.23.jar:8.5.23]
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) [tomcat-embed-core-8.5.23.jar:8.5.23]
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459) [tomcat-embed-core-8.5.23.jar:8.5.23]
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.23.jar:8.5.23]
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) [na:1.8.0_60]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) [na:1.8.0_60]
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.23.jar:8.5.23]
at java.lang.Thread.run(Unknown Source) [na:1.8.0_60]
我还在堆栈溢出的其他线程上研究了此异常(例如 What is a NullPointerException, and how do I fix it? )
我理解错误背后的概念，但无法找出初始化联盟对象的正确方法。 谢谢!
这是我的 Controller :
@Controller
public class HomeController {
@Autowired
UserLoginRepository userRepository;
@Autowired
TeamRepository teamRepository;
@Autowired
GameRepository gameRepository;
@Autowired
LeagueRepository leagueRepository;
@RequestMapping(value="/parsegames", method=RequestMethod.GET)
public String index(Game game) {
return "parseGame";
}
@RequestMapping(value = "/parsegames", method = RequestMethod.POST)
public String addNewPost(@Valid Model model) throws IOException {
Document doc = Jsoup.connect("http://www.irishrugby.ie/club/ulsterbankleagueandcup/fixtures.php").get();
Elements kelime = doc.select("tr[id^=fixturerow]");
for(Element sectd:kelime){
Elements tds = sectd.select("td");
String result = tds.get(0).text();
String result1 = tds.get(1).text();
String result2 = tds.get(2).text();
String result3 = tds.get(3).text();
String result4 = tds.get(4).text();
String result5 = tds.get(5).text();
String result6 = tds.get(6).text();
String result7 = tds.get(7).text();
//creates a new game object
Game game = new Game();
game.setDatePlayed(result);
game.setFinalScore(result4);
//searches db for team with the name then adds the team
to the game homeside
Team team = teamRepository.findByTeamName(result3);
game.setHomeSide(team);
Team team2 = teamRepository.findByTeamName(result5);
game.setAwaySide(team2);
//saves full game info to db
gameRepository.save(game);
League league = leagueRepository.findByLeagueName(result2);
league.setLeagueName("Still");
league.setDivision(result2);
league.setSeason("17/18");
league.addTeam(team);
league.addTeam(team2);
league.addGame(game);
leagueRepository.save(league);
}
return "parseresult";
}
这里是 leagueRepository:
@Repository
public interface LeagueRepository extends JpaRepository<League, Long> {
League findByLeagueName(String leaguename);
}
这是我的联赛类(class):
@Entity
public class League {
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private int leagueId;
private String season;
private String leagueName;
private String division;
// league has many matches and is one to many with teams
@OneToMany(fetch=FetchType.LAZY, cascade=CascadeType.ALL)
public Set<Game> games;
@OneToMany(fetch=FetchType.LAZY, cascade=CascadeType.ALL)
public Set<Team> teams;
public League()
{
}
public League(String leagueName, String division, String season) {
super();
this.season = season;
this.leagueName = leagueName;
this.division = division;
}
public League(int leagueId, String season, String leagueName,
String division, Set<Game> games, Set<Team> teams) {
super();
this.leagueId = leagueId;
this.season = season;
this.leagueName = leagueName;
this.division = division;
this.games = games;
this.teams = teams;
}
public String getDivision() {
return division;
}
public void setDivision(String division) {
this.division = division;
}
public int getLeagueId() {
return leagueId;
}
public void setLeagueId(int leagueId) {
this.leagueId = leagueId;
}
public String getSeason() {
return season;
}
public void setSeason(String season) {
this.season = season;
}
public String getLeagueName() {
return leagueName;
}
public void setLeagueName(String leagueName) {
this.leagueName = leagueName;
}
public Set<Game> getGames() {
return games;
}
public void setGames(Set<Game> games) {
this.games = games;
}
public Set<Team> getTeams() {
return teams;
}
public void setTeams(Set<Team> teams) {
this.teams = teams;
}
public void addTeam(Team team){
teams.add(team);
}
public void addGame(Game game){
games.add(game);
}
}
最佳答案
在您的 League.class 中添加以下内容:
@OneToMany(cascade=CascadeType.ALL)
@LazyCollection(LazyCollectionOption.FALSE)
public Set<Game> games = new HashSet();
而不是
@OneToMany(fetch=FetchType.LAZY, cascade=CascadeType.ALL)
public Set<Game> games;
关于java - 一对多关系空指针异常，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/47797014/