Spring Boot集成SpringFox Swagger的Pageable参数问题

Spring Boot项目中常使用springfox-swagger来生成REST API文档，使用springfox-swagger-ui进行API测试。

<dependency>
    <groupId>io.springfox</groupId>
    <artifactId>springfox-swagger2</artifactId>
    <version>2.8.0</version>
</dependency>
<dependency>
    <groupId>io.springfox</groupId>
    <artifactId>springfox-swagger-ui</artifactId>
    <version>2.8.0</version>
</dependency>

REST API方法的参数含有org.springframework.data.domain.Pageable时，如未进行其它配置，Swagger根据接口Pageable的get/is方法生成了pageNumber、pageSize、offset、paged、unpaged、sort.sorted、sort.unsorted等参数，但实际上这些参数是无效的。

@ApiOperation(value = "Find airlines")
@GetMapping(value = "/airlines")
public Page<Airline> searchAirlines(Airline airline, Pageable pageable) {
    return repository.findAll(org.springframework.data.domain.Example.of(airline), pageable);
 }

Spring Boot解析Pageable参数的过程请查看org.springframework.data.web.PageableHandlerMethodArgumentResolver的resolveArgument()方法：

@Override
public Pageable resolveArgument(MethodParameter methodParameter, @Nullable ModelAndViewContainer mavContainer,
        NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) {

    assertPageableUniqueness(methodParameter);

    Optional<Pageable> defaultOrFallback = getDefaultFromAnnotationOrFallback(methodParameter).toOptional();

    String pageString = webRequest.getParameter(getParameterNameToUse(pageParameterName, methodParameter));
    String pageSizeString = webRequest.getParameter(getParameterNameToUse(sizeParameterName, methodParameter));

    Optional<Integer> page = parseAndApplyBoundaries(pageString, Integer.MAX_VALUE, true);
    Optional<Integer> pageSize = parseAndApplyBoundaries(pageSizeString, maxPageSize, false);

    if (!(page.isPresent() && pageSize.isPresent()) && !defaultOrFallback.isPresent()) {
        return Pageable.unpaged();
    }

    int p = page.orElseGet(() -> defaultOrFallback.map(Pageable::getPageNumber).orElseThrow(IllegalStateException::new));
    int ps = pageSize.orElseGet(() -> defaultOrFallback.map(Pageable::getPageSize).orElseThrow(IllegalStateException::new));

    // Limit lower bound
    ps = ps < 1 ? defaultOrFallback.map(Pageable::getPageSize).orElseThrow(IllegalStateException::new) : ps;
    // Limit upper bound
    ps = ps > maxPageSize ? maxPageSize : ps;

    Sort sort = sortResolver.resolveArgument(methodParameter, mavContainer, webRequest, binderFactory);

    return PageRequest.of(p, ps,
            sort.isSorted() ? sort : defaultOrFallback.map(Pageable::getSort).orElseGet(Sort::unsorted));
}

其中使用的参数名称为page、size、sort，因此通过Swagger传入的参数是无效的。解决方法有以下几种：

@ApiImplicitParams

使用@ApiImplicitParams隐式添加page、size、sort参数，使用@ApiIgnore忽略Pageable参数。缺点，每个方法都要添加，比较繁琐。

@ApiOperation(value = "Find airlines")
@ApiImplicitParams({
    @ApiImplicitParam(name = "page", dataType = "integer", paramType = "query", value = "Results page you want to retrieve (0..N)"),
    @ApiImplicitParam(name = "size", dataType = "integer", paramType = "query", value = "Number of records per page."),
    @ApiImplicitParam(name = "sort", allowMultiple = true, dataType = "string", paramType = "query",
        value = "Sorting criteria in the format: property(,asc|desc). Default sort order is ascending. Multiple sort criteria are supported.")
})
@GetMapping(value = "/airlines")
public Page<Airline> searchAirlines(Airline airline, @ApiIgnore Pageable pageable) {
    return repository.findAll(org.springframework.data.domain.Example.of(airline), pageable);
}

OperationBuilderPlugin

添加OperationBuilderPlugin组件，遇到Pageable时自动添加page、size、sort参数，同时也需使用@ApiIgnore忽略Pageable参数。

import com.fasterxml.classmate.ResolvedType;
import com.fasterxml.classmate.TypeResolver;
import com.google.common.base.Function;
import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.Ordered;
import org.springframework.core.annotation.Order;
import org.springframework.data.domain.Pageable;
import org.springframework.stereotype.Component;
import springfox.documentation.builders.ParameterBuilder;
import springfox.documentation.schema.ResolvedTypes;
import springfox.documentation.schema.TypeNameExtractor;
import springfox.documentation.schema.ModelReference;
import springfox.documentation.service.Parameter;
import springfox.documentation.service.ResolvedMethodParameter;
import springfox.documentation.spi.DocumentationType;
import springfox.documentation.spi.schema.contexts.ModelContext;
import springfox.documentation.spi.service.OperationBuilderPlugin;
import springfox.documentation.spi.service.contexts.OperationContext;
import springfox.documentation.spi.service.contexts.ParameterContext;

import static com.google.common.collect.Lists.newArrayList;
import static springfox.documentation.spi.schema.contexts.ModelContext.inputParam;

@Component
@Order(Ordered.LOWEST_PRECEDENCE)
public class PageableParameterReader implements OperationBuilderPlugin {
    private final TypeNameExtractor nameExtractor;
    private final TypeResolver resolver;
    private final ResolvedType pageableType;

    @Autowired
    public PageableParameterReader(TypeNameExtractor nameExtractor, TypeResolver resolver) {
        this.nameExtractor = nameExtractor;
        this.resolver = resolver;
        this.pageableType = resolver.resolve(Pageable.class);
    }

    @Override
    public void apply(OperationContext context) {
        List<ResolvedMethodParameter> methodParameters = context.getParameters();
        List<Parameter> parameters = newArrayList();

        for (ResolvedMethodParameter methodParameter : methodParameters) {
            ResolvedType resolvedType = methodParameter.getParameterType();

            if (pageableType.equals(resolvedType)) {
                ParameterContext parameterContext = new ParameterContext(methodParameter,
                        new ParameterBuilder(),
                        context.getDocumentationContext(),
                        context.getGenericsNamingStrategy(),
                        context);
                Function<ResolvedType, ? extends ModelReference> factory = createModelRefFactory(parameterContext);

                ModelReference intModel = factory.apply(resolver.resolve(Integer.TYPE));
                ModelReference stringModel = factory.apply(resolver.resolve(List.class, String.class));

                parameters.add(new ParameterBuilder()
                        .parameterType("query")
                        .name("page")
                        .modelRef(intModel)
                        .description("Results page you want to retrieve (0..N)").build());
                parameters.add(new ParameterBuilder()
                        .parameterType("query")
                        .name("size")
                        .modelRef(intModel)
                        .description("Number of records per page").build());
                parameters.add(new ParameterBuilder()
                        .parameterType("query")
                        .name("sort")
                        .modelRef(stringModel)
                        .allowMultiple(true)
                        .description("Sorting criteria in the format: property(,asc|desc). "
                                + "Default sort order is ascending. "
                                + "Multiple sort criteria are supported.")
                        .build());
                context.operationBuilder().parameters(parameters);
            }
        }
    }

    @Override
    public boolean supports(DocumentationType delimiter) {
        return true;
    }

    private Function<ResolvedType, ? extends ModelReference> createModelRefFactory(ParameterContext context) {
        ModelContext modelContext = inputParam(
                context.getGroupName(),
                context.resolvedMethodParameter().getParameterType(),
                context.getDocumentationType(),
                context.getAlternateTypeProvider(),
                context.getGenericNamingStrategy(),
                context.getIgnorableParameterTypes());
        return ResolvedTypes.modelRefFactory(modelContext, nameExtractor);
    }
}

AlternateTypeRuleConvention

import com.fasterxml.classmate.TypeResolver;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.Ordered;
import org.springframework.data.domain.Pageable;
import springfox.documentation.builders.AlternateTypeBuilder;
import springfox.documentation.builders.AlternateTypePropertyBuilder;
import springfox.documentation.schema.AlternateTypeRule;
import springfox.documentation.schema.AlternateTypeRuleConvention;

import java.lang.reflect.Type;
import java.util.List;

import static com.google.common.collect.Lists.newArrayList;
import static springfox.documentation.schema.AlternateTypeRules.newRule;

@Configuration
@SuppressWarnings("SpringJavaAutowiringInspection")
public class SpringDataConfiguration {

    @Bean
    public AlternateTypeRuleConvention pageableConvention(final TypeResolver resolver) {
        return new AlternateTypeRuleConvention() {
            @Override
            public int getOrder() {
                return Ordered.LOWEST_PRECEDENCE;
            }

            @Override
            public List<AlternateTypeRule> rules() {
                return newArrayList(newRule(resolver.resolve(Pageable.class), resolver.resolve(pageableMixin())));
            }
        };
    }

    private Type pageableMixin() {
        return new AlternateTypeBuilder()
                .fullyQualifiedClassName(String.format("%s.generated.%s", Pageable.class.getPackage().getName(), Pageable.class.getSimpleName()))
                .withProperties(newArrayList(property(Integer.class, "page"), property(Integer.class, "size"), property(String.class, "sort")))
                .build();
    }

    private AlternateTypePropertyBuilder property(Class<?> type, String name) {
        return new AlternateTypePropertyBuilder()
                .withName(name)
                .withType(type)
                .withCanRead(true)
                .withCanWrite(true);
    }
}

这是springfox文档中介绍的方法，这种方法创建了一个in-memory type，但我未找到添加说明的方法。可以自定义一个Page class：

import com.fasterxml.classmate.TypeResolver;
import io.swagger.annotations.ApiModel;
import io.swagger.annotations.ApiModelProperty;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.Ordered;
import org.springframework.data.domain.Pageable;
import springfox.documentation.schema.AlternateTypeRule;
import springfox.documentation.schema.AlternateTypeRuleConvention;

import java.util.List;

import static com.google.common.collect.Lists.newArrayList;
import static springfox.documentation.schema.AlternateTypeRules.newRule;

@Configuration
@SuppressWarnings("SpringJavaAutowiringInspection")
public class SpringDataConfiguration {

    @Bean
    public AlternateTypeRuleConvention pageableConvention(final TypeResolver resolver) {
        return new AlternateTypeRuleConvention() {
            @Override
            public int getOrder() {
                return Ordered.HIGHEST_PRECEDENCE;
            }

            @Override
            public List<AlternateTypeRule> rules() {
                return newArrayList(newRule(resolver.resolve(Pageable.class), resolver.resolve(Page.class)));
            }
        };
    }

    @ApiModel
    static class Page {
        @ApiModelProperty("Results page you want to retrieve (0..N)")
        private Integer page;

        @ApiModelProperty("Number of records per page")
        private Integer size;

        @ApiModelProperty("Sorting criteria in the format: property(,asc|desc). Default sort order is ascending. Multiple sort criteria are supported.")
        private List<String> sort;

        public Integer getPage() {
            return page;
        }

        public void setPage(Integer page) {
            this.page = page;
        }

        public Integer getSize() {
            return size;
        }

        public void setSize(Integer size) {
            this.size = size;
        }

        public List<String> getSort() {
            return sort;
        }

        public void setSort(List<String> sort) {
            this.sort = sort;
        }
    }
}

参考文档

Swagger IO
Swagger Github
Tools and Integrations
SpringFox