NullPointerException when trying to define a custom PropertyMap

Question

I'm using ModelMapper the following way :

I have a few converter classes that are Spring components and they register custom ModelMapper mappings

@Component
public class FooConverter {

    @Autowired
    private ModelMapper modelMapper;

    public static final PropertyMap<Foo, FooModel> FOO_TO_FOO_MODEL_MAP = new PropertyMap<Foo, FooModel>() {
        @Override
        protected void configure() {
            map().setTimeZone(source.getTimeZone().getID());
        }
    };

    @PostConstruct
    public void init() {
        modelMapper.addMappings(FOO_TO_FOO_MODEL_MAP);
    }
}

But I get the following error when Spring starts because the configure function gets called and the source is null.

How is that supposed to work?

Am I using it wrong?

1 error
    at org.modelmapper.internal.Errors.throwConfigurationExceptionIfErrorsExist(Errors.java:241)
    at org.modelmapper.internal.ExplicitMappingBuilder.build(ExplicitMappingBuilder.java:244)
    at org.modelmapper.internal.ExplicitMappingBuilder.build(ExplicitMappingBuilder.java:96)
    at org.modelmapper.internal.TypeMapImpl.addMappings(TypeMapImpl.java:92)
    at org.modelmapper.internal.TypeMapStore.getOrCreate(TypeMapStore.java:124)
    at org.modelmapper.ModelMapper.addMappings(ModelMapper.java:113)
    at com.agilitypr.neptune.account.api.v1.controllers.PreferenceController.getUserAccountPreferences(PreferenceController.java:63)
    at com.agilitypr.neptune.account.api.v1.controllers.PreferenceController$$FastClassBySpringCGLIB$$3559fcbb.invoke(<generated>)
    at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:746)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)
    at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:88)
    at com.agilitypr.neptune.account.api.v1.filters.AuthorizationFilter.doAuthorize(AuthorizationFilter.java:52)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:644)
    at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:633)
    at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:70)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:174)
    at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:88)
    at com.agilitypr.neptune.account.api.v1.filters.AuthenticationFilter.doAuthenticate(AuthenticationFilter.java:48)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:644)
    at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:633)
    at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:70)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:174)
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185)
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:688)
    at com.agilitypr.neptune.account.api.v1.controllers.PreferenceController$$EnhancerBySpringCGLIB$$a4d3aeda.getUserAccountPreferences(<generated>)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:209)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:877)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:783)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:991)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:974)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:866)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:687)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:851)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
    at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:865)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1655)
    at org.eclipse.jetty.websocket.server.WebSocketUpgradeFilter.doFilter(WebSocketUpgradeFilter.java:215)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1642)
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1642)
    at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:109)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1642)
    at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1642)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1642)
    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:533)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:146)
    at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:548)
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
    at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:257)
    at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:1595)
    at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:255)
    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1317)
    at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:203)
    at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:473)
    at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:1564)
    at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:201)
    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1219)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:144)
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
    at org.eclipse.jetty.server.Server.handle(Server.java:531)
    at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:352)
    at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:260)
    at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:281)
    at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:102)
    at org.eclipse.jetty.io.ChannelEndPoint$2.run(ChannelEndPoint.java:118)
    at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:762)
    at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:680)
    at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NullPointerException
    at org.modelmapper.internal.ExplicitMappingBuilder$ExplicitMappingInterceptor.access$000(ExplicitMappingBuilder.java:304)
    at org.modelmapper.internal.ExplicitMappingBuilder.createAccessorProxies(ExplicitMappingBuilder.java:287)
    at org.modelmapper.internal.ExplicitMappingBuilder.createProxies(ExplicitMappingBuilder.java:277)
    at org.modelmapper.internal.ExplicitMappingBuilder.visitPropertyMap(ExplicitMappingBuilder.java:266)
    at org.modelmapper.PropertyMap.configure(PropertyMap.java:386)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.modelmapper.internal.ExplicitMappingBuilder.build(ExplicitMappingBuilder.java:227)
    ... 90 more

The bean is declared like this and Foo and FooModel are not final

@Configuration
public class FooConfiguration {
    @Bean
    public ModelMapper modelMapper() {
        return new ModelMapper();
    }
}

Important edit

Actually, even when I create the mapping explicitly in the function inside a main class, I get the same NullPointerException.

public class main {
public static void main(String[] args) {
    ModelMapper mapper = new ModelMapper();
    final PropertyMap<Foo, FooModel> FOO_TO_FOO_MODEL_MAP = new PropertyMap<Foo, FooModel>() {
       @Override
       protected void configure() {
           map().setTimeZone(source.getTimeZone().getID());
       }
    };

    mapper.addMappings(FOO_TO_FOO_MODEL_MAP );
}

}

What is wrong?

I am following the example in their documentation.

EDIT

Deep mapping is working with these

public class InnerFoo {
    private int prop3;

    public int getProp3() {
        return prop3;
    }

    public void setProp3(int prop3) {
        this.prop3 = prop3;
    }

}

public class Foo {
    private InnerFoo innerFoo;

    public InnerFoo getInnerFoo() {
        return innerFoo;
    }

    public void setInnerFoo(InnerFoo innerFoo) {
        this.innerFoo = innerFoo;
    }

}

public class FooModel {
    private int prop2;

    public int getProp2() {
        return prop2;
    }

    public void setProp2(int prop2) {
        this.prop2 = prop2;
    }

}

the problem is only with the TimeZone object so I have to use a converter, which is not ideal.

map().setTimeZone(source.getTimeZone().getID());


public class Foo {
    private TimeZone timeZone;
    //Setters//Getters

}

public class FooModel {
    private String timeZoneId;
    //Setters//Getters
}

Alessandraalessandria

Where is your modelMapper bean defined? – Bronchial

@Bronchial The question is updated. The bean is properly defined and it is not null – Alessandraalessandria

Is Foo or FooModel declared as final? – Zilla

@JanRieke No, they are not. – Alessandraalessandria

You said mapping works with those example classes InnerFoo, Foo l, FooModel. Could you add an example for FooModel which can not be mapped? – Vesicatory

@HeroWanders Added. I guess the timeZone.getId() function has some logic and the basic deep mapping can't handle that. It works only in a converter – Alessandraalessandria

Answer 1

I think this is ultimately due to the fact that ModelMapper can not instantiate TimeZone objects (nor LocalDateTime etc.) at the time of configuring the mapper.

Actually you don't have to configure anything.

ModelMapper mapper = new ModelMapper();

Foo foo = new Foo();
foo.setTimeZone(TimeZone.getDefault());

FooModel model = mapper.map(foo, FooModel.class);
System.out.println(model.getTimeZoneId()); // "Europe/Berlin" here

This works for me. ModelMapper found out that you want to map the TimeZone's property ID to FooModel's property timeZoneId.

Nevertheless, just in case you want to do that manually: Following the docs quickly, I found the concept of converters. Using a Converter which converts TimeZone to String you can do this:

ModelMapper mapper = new ModelMapper();
TypeMap<Foo, FooModel> typeMap = mapper.createTypeMap(Foo.class, FooModel.class);
Converter<TimeZone, String> tzConverter = ctx -> ctx.getSource().getID() + "!!!";
typeMap.addMappings(map -> {
    map.using(tzConverter).map(Foo::getTimeZone, FooModel::setTimeZoneId);
});

Foo foo = new Foo();
foo.setTimeZone(TimeZone.getDefault());

FooModel model = mapper.map(foo, FooModel.class);
System.out.println(model.getTimeZoneId()); // "Europe/Berlin!!!" here

Vesicatory

Thank you. I ended up using a converter. – Alessandraalessandria

Answer 2

For anyone coming across with the same issue: My problem was that I used PropertyMap with anonymous implementation like the documentation suggested within a spring configuration. This messed up within the ExplicitMappingBuilder. What I have now is the following:

@Configuration
public class ApplicationConfig {

    @Bean
    public ModelMapper modelMapper() {
        ModelMapper modelMapper = new ModelMapper();
        modelMapper.addMappings(new UserPropertyMap());
        return modelMapper;
    }
}

My UserPropertyMap looks like this:

public class UserPropertyMap extends PropertyMap<UserRepresentation, UserDTO> {
    @Override
    protected void configure() {
        map().setUserName(source.getUsername());
    }
}

This worked like a charm in Spring Boot 2.

Christenechristening

Nice catch, just a shame it doesn't seems to work on Android :( – Susurrus

Answer 3

Autowire using constructor like

public FooConverter(ModelMapper modelMapper){
   this.modelMapper = modelMapper;
}

also make sure your ModelMapper bean has been defined in your spring config class like below:

@Bean
public ModelMapper modelMapper() {
    return new ModelMapper();
}

Haleakala

Constructor-based wiring only makes the lack of a bean more obvious, but if the bean were defined and wired up properly you wouldn't be able to tell a difference between field-based and constructor-based wiring. This is fixing a symptom. – Bronchial

It is always prefered to use Construtor based wiring. It makes sure injecting beans are initialized before creating the Bean for the class. – Haleakala

The bean is properly defined and it's not null – Alessandraalessandria

@SayantanMandal constructor based wiring becomes really difficult in real world! – Pharyngology