Java for Web学习笔记（一一六）：Spring Data（4）分页例子（上）

例子说明

在例子中，我们将学习如何分页显示用户的评论。

加入spring data

引入jar包

加入spring data在pom中引入

<dependency>
    <groupId>org.springframework.data</groupId>
    <artifactId>spring-data-jpa</artifactId>
    <version>1.11.10.RELEASE</version>
</dependency>

在Root上下文的配置

@Configuration
@EnableAsync( mode = AdviceMode.PROXY, proxyTargetClass = false, order = Ordered.HIGHEST_PRECEDENCE )
@EnableTransactionManagement( mode = AdviceMode.PROXY, proxyTargetClass = false, order = Ordered.LOWEST_PRECEDENCE )
@EnableJpaRepositories( basePackages = "cn.wei.flowingflying.customer_support.site.repositories",
                        entityManagerFactoryRef = "entityManagerFactoryBean",
                        transactionManagerRef = "jpaTransactionManager"
)
@EnableScheduling
@ComponentScan( basePackages = "cn.wei.flowingflying.customer_support.site",
                excludeFilters = @ComponentScan.Filter({Controller.class,ControllerAdvice.class,Endpoint.class}))
public class RootContextConfiguration implements AsyncConfigurer, SchedulingConfigurer{
    ......
}

在DispatchServlet上下文的配置

简单地可以加上@EnableSpringDataWebSupport，在例子中，我们采用通过代码定制化设置的方式。

@Configuration
@EnableWebMvc
@ComponentScan( basePackages = "cn.wei.flowingflying.customer_support.site",
                useDefaultFilters = false,
                includeFilters = @ComponentScan.Filter(WebController.class))
public class WebServletContextConfiguration extends WebMvcConfigurerAdapter{
    private static final Logger log = LogManager.getLogger();	
    @Inject private ApplicationContext applicationContext;
    ......     

    //【1】SortHandlerMethodArgumentResolver，转换请求中的Sort参数
    //【2】PageableHandlerMethodArgumentResolver，转换请求中的Pageable参数
    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers) {
       //【1.1】设置缺省的排序方式：根据id的升序
       Sort defaultSort = new Sort(new Sort.Order(Sort.Direction.ASC, "id"));
       //【2.1】设置缺省的分页情况，第一个参数是zero-based page index，如果显示第一页就填0，每页10个条目，采用缺省的排序方式（根据id的升序）
       Pageable defaultPageable = new PageRequest(0, 10, defaultSort);

       //【1.2】设置Sort的转换器：自动转换请求参数或者@SortDefault标记
       SortHandlerMethodArgumentResolver sortResolver = new SortHandlerMethodArgumentResolver();
       sortResolver.setSortParameter("paging.sort"); //请求中的排序参数为paging.sort，请对照后面的jsp代码
       sortResolver.setFallbackSort(defaultSort);
       //【2.2】设置Page的转换器：从web请求中获取也信息，并注入到控制器方法中的Pageable对象中
       PageableHandlerMethodArgumentResolver pageableResolver = new PageableHandlerMethodArgumentResolver(sortResolver);
       pageableResolver.setMaxPageSize(100);
       pageableResolver.setOneIndexedParameters(true); //页的序号从1开始，缺省是false
       pageableResolver.setPrefix("paging.");
       pageableResolver.setFallbackPageable(defaultPageable);
	
       //【1.3】添加解析器
       resolvers.add(sortResolver);
       //【2.3】添加解析器
       resolvers.add(pageableResolver);
   } 

   //org.springframework.data.repository.support.DomainClassConverter：将请求参数和路径进行转换
   @Override
   public void addFormatters(FormatterRegistry registry) {
       if(!(registry instanceof FormattingConversionService)){
           log.warn("Unable to register Spring Data JPA converter.");
           return;
       }
        
       // DomainClassConverter adds itself to the registry。
       // org.springframework.core.convert.converter.Converter to convert arbitrary input into domain classes managed by Spring Data CrudRepositorys. The implementation uses a ConversionService in turn to convert the source type into the domain class' id type which is then converted into a domain class object by using a CrudRepository. 也就是根据id自动获得一个entity
       DomainClassConverter<FormattingConversionService> converter =
                new DomainClassConverter<>((FormattingConversionService)registry);
       converter.setApplicationContext(this.applicationContext);
    }
   ......
}

如果有多个dispatchServlet，如果需要使用到分页和排序，我们也进行相应的的设置，相关的缺省参数不一样，代码例子如下：

@Configuration
@EnableWebMvc
@ComponentScan(
        basePackages = "cn.wei.flowingflying.customer_support.site",
        useDefaultFilters = false,
        includeFilters =
        @ComponentScan.Filter({RestEndpoint.class, RestEndpointAdvice.class})
)
public class RestServletContextConfiguration extends WebMvcConfigurerAdapter{
    private static final Logger log = LogManager.getLogger();
    @Inject ApplicationContext applicationContext;
    ......

    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers) {
        Sort defaultSort = new Sort(new Sort.Order(Sort.Direction.ASC, "id"));
        Pageable defaultPageable = new PageRequest(0, 20, defaultSort);

        SortHandlerMethodArgumentResolver sortResolver = new SortHandlerMethodArgumentResolver();
        sortResolver.setSortParameter("$paging.sort"); 
        sortResolver.setFallbackSort(defaultSort);

        PageableHandlerMethodArgumentResolver pageableResolver = new PageableHandlerMethodArgumentResolver(sortResolver);
        pageableResolver.setMaxPageSize(200);
        pageableResolver.setOneIndexedParameters(true); 
        pageableResolver.setPrefix("$paging."); 
        pageableResolver.setFallbackPageable(defaultPageable);

        resolvers.add(sortResolver);
        resolvers.add(pageableResolver);
    }

    @Override
    public void addFormatters(FormatterRegistry registry){
        if(!(registry instanceof FormattingConversionService)){
            log.warn("Unable to register Spring Data JPA converter.");
            return;
        }

        DomainClassConverter<FormattingConversionService> converter =
                new DomainClassConverter<>((FormattingConversionService)registry);
        converter.setApplicationContext(this.applicationContext);
    }    
}

对于RESTful接口分页的信息除了URL外，例如http://localhost:8080/persons?page=1&size=5&sort，还可以使用HTTP Range headers： Range, Content-Range, If-Range, Accept-Ranges，而相关的返回代码：

206 (Partial Content)
413 (Request Entity Too Large)
416 (Requested Range Not Satisfiable).