Spring Boot 页面反序列化 - PageImpl 无构造函数答案

【问题标题】：Spring Boot Page Deserialization - PageImpl No constructorSpring Boot 页面反序列化 - PageImpl 无构造函数
【发布时间】：2019-02-28 14:50:43
【问题描述】：

尝试对从 Spring Boot 接收页面进行单元测试。如果与 javascript 一起使用，该页面可以很容易地被反序列化，但使用 java，它会失败。为 spring 添加了一个默认构造函数（这是另一个 stackoverflow 帖子中接受的答案），但它在这里不起作用。

单元测试

@Test
public void test_read_pagination_happy(@Autowired ObservationSet set) {

    repository.save(set);

    final HttpEntity<String> authHeaders = authentication.convert("", authSuccess);
    final ParameterizedTypeReference<RestResponsePage<ObservationSet>> responseType = new ParameterizedTypeReference<RestResponsePage<ObservationSet>>() {
    };
    // final ResponseEntity<String> result = restTemplate.exchange(base + "/api/v1/observationset", HttpMethod.GET, authHeaders, String.class);
    final ResponseEntity<RestResponsePage<ObservationSet>> result = restTemplate.exchange(base + "/api/v1/observationset", HttpMethod.GET, authHeaders,
                    responseType);
    System.out.println(result.getBody());
    assertSame(HttpStatus.OK, result.getStatusCode(), "incorrect status code");
}

RestRespongePage 类

class RestResponsePage<T> extends PageImpl<T> {

    private static final long serialVersionUID = 3248189030448292002L;

    public RestResponsePage(List<T> content, Pageable pageable, long total) {
        super(content, pageable, total);
    }

    public RestResponsePage(List<T> content) {
        super(content);
    }

    public RestResponsePage() {
        super(new ArrayList<T>());
    }

}

```

代码在 github 上可用 --> https://github.com/OpenPCM/openpcm-server/blob/integration-test/src/test/java/org/openpcm/controller/ObservationSetControllerIntTest.java

反序列化抛出此错误：

org.springframework.http.converter.HttpMessageConversionException: Type definition error: [simple type, class org.springframework.data.domain.Pageable]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `org.springframework.data.domain.Pageable` (no Creators, like default construct, exist): abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information
 at [Source: (PushbackInputStream); line: 1, column: 294] (through reference chain: org.openpcm.controller.RestResponsePage["pageable"])
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:240)
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.read(AbstractJackson2HttpMessageConverter.java:225)
    at org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:100)
    at org.springframework.web.client.RestTemplate$ResponseEntityResponseExtractor.extractData(RestTemplate.java:959)
    at org.springframework.web.client.RestTemplate$ResponseEntityResponseExtractor.extractData(RestTemplate.java:942)
    at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:689)
    at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:644)
    at org.springframework.web.client.RestTemplate.exchange(RestTemplate.java:593)
    at org.springframework.boot.test.web.client.TestRestTemplate.exchange(TestRestTemplate.java:843)
    at org.openpcm.controller.ObservationSetControllerIntTest.test_read_pagination_happy(ObservationSetControllerIntTest.java:85)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:564)
    at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:436)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:115)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$6(TestMethodTestDescriptor.java:170)
    at org.junit.jupiter.engine.execution.ThrowableCollector.execute(ThrowableCollector.java:40)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:166)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:113)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:58)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.lambda$executeRecursively$3(HierarchicalTestExecutor.java:112)
    at org.junit.platform.engine.support.hierarchical.SingleTestExecutor.executeSafely(SingleTestExecutor.java:66)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.executeRecursively(HierarchicalTestExecutor.java:108)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.execute(HierarchicalTestExecutor.java:79)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.lambda$executeRecursively$2(HierarchicalTestExecutor.java:120)
    at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:184)
    at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:177)
    at java.base/java.util.Iterator.forEachRemaining(Iterator.java:133)
    at java.base/java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801)
    at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
    at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
    at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151)
    at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174)
    at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
    at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:430)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.lambda$executeRecursively$3(HierarchicalTestExecutor.java:120)
    at org.junit.platform.engine.support.hierarchical.SingleTestExecutor.executeSafely(SingleTestExecutor.java:66)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.executeRecursively(HierarchicalTestExecutor.java:108)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.execute(HierarchicalTestExecutor.java:79)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.lambda$executeRecursively$2(HierarchicalTestExecutor.java:120)
    at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:184)
    at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:177)
    at java.base/java.util.Iterator.forEachRemaining(Iterator.java:133)
    at java.base/java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801)
    at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
    at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
    at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151)
    at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174)
    at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
    at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:430)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.lambda$executeRecursively$3(HierarchicalTestExecutor.java:120)
    at org.junit.platform.engine.support.hierarchical.SingleTestExecutor.executeSafely(SingleTestExecutor.java:66)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.executeRecursively(HierarchicalTestExecutor.java:108)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.execute(HierarchicalTestExecutor.java:79)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:55)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:43)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:170)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:154)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:90)
    at org.eclipse.jdt.internal.junit5.runner.JUnit5TestReference.run(JUnit5TestReference.java:89)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:41)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:541)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:763)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:463)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:209)
Caused by: com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `org.springframework.data.domain.Pageable` (no Creators, like default construct, exist): abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information
 at [Source: (PushbackInputStream); line: 1, column: 294] (through reference chain: org.openpcm.controller.RestResponsePage["pageable"])
    at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:67)
    at com.fasterxml.jackson.databind.DeserializationContext.reportBadDefinition(DeserializationContext.java:1451)
    at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1027)
    at com.fasterxml.jackson.databind.deser.AbstractDeserializer.deserialize(AbstractDeserializer.java:265)
    at com.fasterxml.jackson.databind.deser.impl.FieldProperty.deserializeAndSet(FieldProperty.java:136)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:288)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:151)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4013)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3084)
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:237)
    ... 65 more

【问题讨论】：

请提供例外的文字。（请参考：idownvotedbecau.se/imageofanexception）
一种解决方法是不将 Page 公开为来自控制器端点的响应类型，而是返回 List。 Page 有一个方法getContent()，您可以调用该方法将 Page 转换为 List。正如我所说，不是修复，而是解决方法。
@alexrolea 我实际上想返回页面，而不仅仅是列表，所以如果你在网络客户端中，你可以通过页面标签
@Prashant 删除了图片并添加了文字
是的，但是如果您从响应中隐藏页面对象“numberOfPages”等，UI 将不知道有多少可能的页面。您可以硬编码每页要显示多少个元素，但您不知道总页码，这不允许您显示 page1...page127 等，您基本上只会知道您制作后存在的页码调用并取回不同数量的元素我现在找到了如何完成这项工作的答案

标签： java spring spring-boot pagination deserialization

【解决方案1】：

在这里的不同帖子中找到了答案。这不是应该被接受的答案

Spring RestTemplate with paginated API

@rvheddeg 的答案是正确的。您只需要输入@JsonCreator 并提供一个包含所有属性的构造函数，这是我的 RestResponsePage 类来解决这个问题。

class RestResponsePage<T> extends PageImpl<T> {

    private static final long serialVersionUID = 3248189030448292002L;

    @JsonCreator(mode = JsonCreator.Mode.PROPERTIES)
    public RestResponsePage(@JsonProperty("content") List<T> content, @JsonProperty("number") int number, @JsonProperty("size") int size,
                    @JsonProperty("totalElements") Long totalElements, @JsonProperty("pageable") JsonNode pageable, @JsonProperty("last") boolean last,
                    @JsonProperty("totalPages") int totalPages, @JsonProperty("sort") JsonNode sort, @JsonProperty("first") boolean first,
                    @JsonProperty("numberOfElements") int numberOfElements) {
        super(content, PageRequest.of(number, size), totalElements);
    }

    public RestResponsePage(List<T> content, Pageable pageable, long total) {
        super(content, pageable, total);
    }

    public RestResponsePage(List<T> content) {
        super(content);
    }

    public RestResponsePage() {
        super(new ArrayList<T>());
    }

}

【讨论】：

对于 Spring 2.3.3 我遇到编译错误：new PageRequest(page, size) 具有受保护的访问权限。你可以使用PageRequest.of(page, size)。

【解决方案2】：

有一种更简单的方法 - 为 Page 接口创建和注册自定义反序列化器。所以用法很简单：

//Catalog is the paged entity
Page<Catalog> page = objectMapper.readValue(content, new TypeReference<Page<Catalog>>() {});

ObjectMapper 配置：

ObjectMapper objectMapper= new ObjectMapper();
objectMapper.registerModule(new PageModule());

页面模块：

public class PageModule extends SimpleModule {
    private static final long serialVersionUID = 1L;

    public PageModule() {
        addDeserializer(Page.class, new PageDeserializer());
    }
}

PageDeserializer：

public class PageDeserializer extends JsonDeserializer<Page<?>> implements ContextualDeserializer {
    private static final String CONTENT = "content";
    private static final String NUMBER = "number";
    private static final String SIZE = "size";
    private static final String TOTAL_ELEMENTS = "totalElements";
    private JavaType valueType;

    @Override
    public Page<?> deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
        final CollectionType valuesListType = ctxt.getTypeFactory().constructCollectionType(List.class, valueType);

        List<?> list = new ArrayList<>();
        int pageNumber = 0;
        int pageSize = 0;
        long total = 0;
        if (p.isExpectedStartObjectToken()) {
            p.nextToken();
            if (p.hasTokenId(JsonTokenId.ID_FIELD_NAME)) {
                String propName = p.getCurrentName();
                do {
                    p.nextToken();
                    switch (propName) {
                        case CONTENT:
                            list = ctxt.readValue(p, valuesListType);
                            break;
                        case NUMBER:
                            pageNumber = ctxt.readValue(p, Integer.class);
                            break;
                        case SIZE:
                            pageSize = ctxt.readValue(p, Integer.class);
                            break;
                        case TOTAL_ELEMENTS:
                            total = ctxt.readValue(p, Long.class);
                            break;
                        default:
                            p.skipChildren();
                            break;
                    }
                } while (((propName = p.nextFieldName())) != null);
            } else {
                ctxt.handleUnexpectedToken(handledType(), p);
            }
        } else {
            ctxt.handleUnexpectedToken(handledType(), p);
        }

        //Note that Sort field of Page is ignored here.
        //Feel free to add more switch cases above to deserialize it as well.  
        return new PageImpl<>(list, PageRequest.of(pageNumber, pageSize), total);
    }

    /**
     * This is the main point here.
     * The PageDeserializer is created for each specific deserialization with concrete generic parameter type of Page.
     */
    @Override
    public JsonDeserializer<?> createContextual(DeserializationContext ctxt, BeanProperty property) {
        //This is the Page actually
        final JavaType wrapperType = ctxt.getContextualType();
        final PageDeserializer deserializer = new PageDeserializer();
        //This is the parameter of Page
        deserializer.valueType = wrapperType.containedType(0);
        return deserializer;
    }
}

【讨论】：

这与接受的答案一样好，其他一些替代方案可能会导致 Blockhound 在反序列化页面时报告阻塞调用。我正在使用 Spring WebFlux。

【解决方案3】：

不得不做一个小改动来忽略空的未知属性：

package ...helper;

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.JsonNode;
import org.springframework.data.domain.PageImpl;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Pageable;

import java.util.ArrayList;
import java.util.List;

@JsonIgnoreProperties(ignoreUnknown = true)
public class RestResponsePage<T> extends PageImpl<T> {
    @JsonCreator(mode = JsonCreator.Mode.PROPERTIES)
    public RestResponsePage(@JsonProperty("content") List<T> content,
                            @JsonProperty("number") int number,
                            @JsonProperty("size") int size,
                            @JsonProperty("totalElements") Long totalElements,
                            @JsonProperty("pageable") JsonNode pageable,
                            @JsonProperty("last") boolean last,
                            @JsonProperty("totalPages") int totalPages,
                            @JsonProperty("sort") JsonNode sort,
                            @JsonProperty("first") boolean first,
                            @JsonProperty("numberOfElements") int numberOfElements) {

        super(content, PageRequest.of(number, size), totalElements);
    }

    public RestResponsePage(List<T> content, Pageable pageable, long total) {
        super(content, pageable, total);
    }

    public RestResponsePage(List<T> content) {
        super(content);
    }

    public RestResponsePage() {
        super(new ArrayList<>());
    }
}

【讨论】：

【解决方案4】：

这有效（org.springframework.cloud:spring-cloud-openfeign-core:2.2.5.RELEASE）：

@Configuration
public class FeignConfigurationFactory {

    @Bean
    public Module pageJacksonModule() {
        return new PageJacksonModule();
    }

    @Bean
    public Module sortJacksonModule() {
        return new SortJacksonModule();
    }
}

【讨论】：

当我作为 jar 运行时，我得到了 java.lang.ClassNotFoundException: feign.codec.EncodeException 和 org.springframework.cloud:spring-cloud-openfeign-core。需要改用org.springframework.cloud:spring-cloud-starter-openfeign。
这对我有用。谢谢。

【解决方案5】：

如果您使用响应并对其进行序列化，则这些解决方案在测试领域中不起作用。我必须自己序列化 List 中的内容:)
在这种情况下，我使用的是 RestAssured 响应。

protected static <T> List<T> getResponsePageDTO(Response response, Class<T> clazz) throws IOException {
    Map<String, Object> objectMap = objectMapper.readValue(response.getBody().print(), Map.class);
    List<Object> content = (List<Object>) objectMap.get("content");
    List<T> result = new ArrayList<>();
    for (Object o : content) {
        result.add(objectMapper.convertValue(o, clazz));
    }
    return result;
}

【讨论】：

这对我有用！

【解决方案6】：

其实spring mvc是通过jackson序列化对象，所以注入一个pageImp序列化器应该可以解决问题。

第 1 步：PageSerializer 类：

   public class PageSerializer extends StdSerializer<PageImpl> {

    public PageSerializer() {
        super(PageImpl.class);
    }

    @Override
    public void serialize(PageImpl value, JsonGenerator gen, SerializerProvider provider) throws IOException {
        gen.writeStartObject();
        gen.writeNumberField("number", value.getNumber());
        gen.writeNumberField("numberOfElements", value.getNumberOfElements());
        gen.writeNumberField("totalElements", value.getTotalElements());
        gen.writeNumberField("totalPages", value.getTotalPages());
        gen.writeNumberField("size", value.getSize());
        gen.writeFieldName("content");
        provider.defaultSerializeValue(value.getContent(), gen);
        gen.writeEndObject();
    }
 }

第二步：注入jackson Moudle：

@Bean
public Module jacksonPageWithJsonViewModule() {
    SimpleModule module = new SimpleModule("jackson-page-with-jsonview",
        unknownVersion());
    module.addSerializer(PageImpl.class, new PageSerializer());
    return module;
}

好的，结束。

【讨论】：

【解决方案7】：

你可以这样做

final PageImplDeserializer<YOUR_CLASS> response = objectMapper.readValue(jsonResponse, new TypeReference<>() {});


public class PageImplDeserializer<T> {
    private List<T> content;
    private int number;
    private int size;
    private Long totalElements;
    private JsonNode pageable;
    private boolean last;
    private int totalPages;
    private JsonNode sort;
    private boolean first;
    private int numberOfElements;

... HERE GETTERS AND SETTERS...

}

【讨论】：

【解决方案8】：

要从页面内容中检索对象，无需编写特定的映射器，使用 objectMapper 和类 org.springframework.data.domain.PageImpl

方法如下：

private <T> List<T> getResponsePageContent(ObjectMapper objectMapper, ResultActions result, Class<T> clazz) throws IOException {
   return  objectMapper.readValue(result.andReturn().getResponse().getContentAsString(), 
                             new TypeReference<PageImpl<T>>() {})
                            .getContent();
}

我是这样使用它的：

List<Book> books = getResponsePageContent(objectMapper, result, Book.class);

【讨论】：