var*_*run 4 spring json spring-mvc jackson
我正在使用spring MVC编写一个休息服务,它产生JSON响应.它应该允许客户端在响应中仅选择给定的字段,这意味着客户端可以将他感兴趣的字段作为url参数来提及?fields=field1,field2.
使用杰克逊注释不能提供我正在寻找的东西,因为它不是动态的,杰克逊的过滤器似乎没有足够的前景.到目前为止,我正在考虑实现一个自定义消息转换器,可以解决这个问题.
有没有其他更好的方法来实现这一目标？我想如果这个逻辑没有与我的服务或控制器耦合.
从Spring 4.2开始,@JsonFilterMappingJacksonValue支持
您可以直接将PropertyFilter注入到控制器中的MappingJacksonValue.
@RestController
public class BookController {
private static final String INCLUSION_FILTER = "inclusion";
@RequestMapping("/novels")
public MappingJacksonValue novel(String[] include) {
@JsonFilter(INCLUSION_FILTER)
class Novel extends Book {}
Novel novel = new Novel();
novel.setId(3);
novel.setTitle("Last summer");
novel.setAuthor("M.K");
MappingJacksonValue res = new MappingJacksonValue(novel);
PropertyFilter filter = SimpleBeanPropertyFilter.filterOutAllExcept(include);
FilterProvider provider = new SimpleFilterProvider().addFilter(INCLUSION_FILTER, filter);
res.setFilters(provider);
return res;
}
或者您可以通过ResponseBodyAdvice声明全局策略.以下示例通过"exclude"参数实现过滤策略.
@ControllerAdvice
public class DynamicJsonResponseAdvice extends AbstractMappingJacksonResponseBodyAdvice {
public static final String EXCLUDE_FILTER_ID = "dynamicExclude";
private static final String WEB_PARAM_NAME = "exclude";
private static final String DELI = ",";
private static final String[] EMPTY = new String[]{};
@Override
protected void beforeBodyWriteInternal(MappingJacksonValue container, MediaType contentType,
MethodParameter returnType, ServerHttpRequest req, ServerHttpResponse res) {
if (container.getFilters() != null ) {
// It will be better to merge FilterProvider
// If 'SimpleFilterProvider.addAll(FilterProvider)' is provided in Jackson, it will be easier.
// But it isn't supported yet.
return;
}
HttpServletRequest baseReq = ((ServletServerHttpRequest) req).getServletRequest();
String exclusion = baseReq.getParameter(WEB_PARAM_NAME);
String[] attrs = StringUtils.split(exclusion, DELI);
container.setFilters(configFilters(attrs));
}
private FilterProvider configFilters(String[] attrs) {
String[] ignored = (attrs == null) ? EMPTY : attrs;
PropertyFilter filter = SimpleBeanPropertyFilter.serializeAllExcept(ignored);
return new SimpleFilterProvider().addFilter(EXCLUDE_FILTER_ID, filter);
}
}
恕我直言，最简单的方法是使用内省动态生成包含选定字段的哈希，然后使用 Json 序列化该哈希。您只需决定可用字段列表是什么（见下文）。
下面是两个能够做到这一点的示例函数，第一个获取所有公共字段和公共 getter，第二个获取当前类及其所有父类中的所有声明字段（包括私有字段）：
public Map<String, Object> getPublicMap(Object obj, List<String> names)
throws IllegalAccessException, IllegalArgumentException, InvocationTargetException {
List<String> gettedFields = new ArrayList<String>();
Map<String, Object> values = new HashMap<String, Object>();
for (Method getter: obj.getClass().getMethods()) {
if (getter.getName().startsWith("get") && (getter.getName().length > 3)) {
String name0 = getter.getName().substring(3);
String name = name0.substring(0, 1).toLowerCase().concat(name0.substring(1));
gettedFields.add(name);
if ((names == null) || names.isEmpty() || names.contains(name)) {
values.put(name, getter.invoke(obj));
}
}
}
for (Field field: obj.getClass().getFields()) {
String name = field.getName();
if ((! gettedFields.contains(name)) && ((names == null) || names.isEmpty() || names.contains(name))) {
values.put(name, field.get(obj));
}
}
return values;
}
public Map<String, Object> getFieldMap(Object obj, List<String> names)
throws IllegalArgumentException, IllegalAccessException {
Map<String, Object> values = new HashMap<String, Object>();
for (Class<?> clazz = obj.getClass(); clazz != Object.class; clazz = clazz.getSuperclass()) {
for (Field field : clazz.getDeclaredFields()) {
String name = field.getName();
if ((names == null) || names.isEmpty() || names.contains(name)) {
field.setAccessible(true);
values.put(name, field.get(obj));
}
}
}
return values;
}
然后，您只需要获取此函数之一（或您可以适应您的要求的函数）的结果并将其与 Jackson 序列化。
如果您对域对象进行自定义编码，则必须在两个不同的地方维护序列化规则：哈希生成和 Jackson 序列化。在这种情况下，您可以简单地使用 Jackson 生成完整的类序列化，然后过滤生成的字符串。这是此类过滤器功能的示例：
public String jsonSub(String json, List<String> names) throws IOException {
if ((names == null) || names.isEmpty()) {
return json;
}
ObjectMapper mapper = new ObjectMapper();
Map<String, Object> map = mapper.readValue(json, HashMap.class);
for (String name: map.keySet()) {
if (! names.contains(name)) {
map.remove(name);
}
}
return mapper.writeValueAsString(map);
}
编辑：在 Spring MVC 中的集成
当您谈到 Web 服务和 Jackson 时，我假设您使用 SpringRestController或ResponseBody注释以及（在幕后）一个MappingJackson2HttpMessageConverter. 如果您改用 Jackson 1，则它应该是MappingJacksonHttpMessageConverter.
我的建议只是添加一个HttpMessageConverter可以使用上述过滤功能之一的新功能，并将实际工作（以及辅助方法）委托给真正的MappingJackson2HttpMessageConverter. 在该write新转换器的方法中，fields由于 Spring ，可以访问最终请求参数而无需显式 ThreadLocal 变量RequestContextHolder。那样 ：
HttpMessageConverter这是此类消息转换器的示例：
public class JsonConverter implements HttpMessageConverter<Object> {
private static final Logger logger = LoggerFactory.getLogger(JsonConverter.class);
// a real message converter that will respond to ancilliary methods and do the actual work
private HttpMessageConverter<Object> delegate =
new MappingJackson2HttpMessageConverter();
// allow configuration of the fields name
private String fieldsParam = "fields";
public void setFieldsParam(String fieldsParam) {
this.fieldsParam = fieldsParam;
}
@Override
public boolean canRead(Class<?> clazz, MediaType mediaType) {
return delegate.canRead(clazz, mediaType);
}
@Override
public boolean canWrite(Class<?> clazz, MediaType mediaType) {
return delegate.canWrite(clazz, mediaType);
}
@Override
public List<MediaType> getSupportedMediaTypes() {
return delegate.getSupportedMediaTypes();
}
@Override
public Object read(Class<? extends Object> clazz, HttpInputMessage inputMessage) throws IOException, HttpMessageNotReadableException {
return delegate.read(clazz, inputMessage);
}
@Override
public void write(Object t, MediaType contentType, HttpOutputMessage outputMessage)
throws IOException, HttpMessageNotWritableException {
// is there a fields parameter in request
String[] fields = ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes())
.getRequest().getParameterValues(fieldsParam);
if (fields != null && fields.length != 0) {
// get required field names
List<String> names = new ArrayList<String>();
for (String field : fields) {
String[] f_names = field.split("\\s*,\\s*");
names.addAll(Arrays.asList(f_names));
}
// special management for Map ...
if (t instanceof Map) {
Map<?, ?> tmap = (Map<?, ?>) t;
Map<String, Object> map = new LinkedHashMap<String, Object>();
for (Entry entry : tmap.entrySet()) {
String name = entry.getKey().toString();
if (names.contains(name)) {
map.put(name, entry.getValue());
}
}
t = map;
} else {
try {
Map<String, Object> map = getMap(t, names);
t = map;
} catch (Exception ex) {
throw new HttpMessageNotWritableException("Error in field extraction", ex);
}
}
}
delegate.write(t, contentType, outputMessage);
}
/**
* Create a Map by keeping only some fields of an object
* @param obj the Object
* @param names names of the fields to keep in result Map
* @return a map containing only requires fields and their value
* @throws IllegalArgumentException
* @throws IllegalAccessException
*/
public static Map<String, Object> getMap(Object obj, List<String> names)
throws IllegalArgumentException, IllegalAccessException {
Map<String, Object> values = new HashMap<String, Object>();
for (Class<?> clazz = obj.getClass(); clazz != Object.class; clazz = clazz.getSuperclass()) {
for (Field field : clazz.getDeclaredFields()) {
String name = field.getName();
if (names.contains(name)) {
field.setAccessible(true);
values.put(name, field.get(obj));
}
}
}
return values;
}
}
如果你想让转换器更通用，你可以定义一个接口
public interface FieldsFilter {
Map<String, Object> getMap(Object obj, List<String> names)
throws IllegalAccessException, IllegalArgumentException, InvocationTargetException;
}
并注入它的实现。
现在您必须要求 Spring MVC 使用该自定义消息控制器。
如果您使用 XML 配置，您只需在<mvc:annotation-driven>元素中声明它：
<mvc:annotation-driven >
<mvc:message-converters>
<bean id="jsonConverter" class="org.example.JsonConverter"/>
</mvc:message-converters>
</mvc:annotation-driven>
如果您使用 Java 配置，它几乎同样简单：
@EnableWebMvc
@Configuration
public class WebConfig extends WebMvcConfigurerAdapter {
@Autowired JsonConverter jsonConv;
@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
converters.add(jsonConv);
StringHttpMessageConverter stringConverter = new StringHttpMessageConverter();
stringConverter.setWriteAcceptCharset(false);
converters.add(new ByteArrayHttpMessageConverter());
converters.add(stringConverter);
converters.add(new ResourceHttpMessageConverter());
converters.add(new SourceHttpMessageConverter<Source>());
converters.add(new AllEncompassingFormHttpMessageConverter());
converters.add(new MappingJackson2HttpMessageConverter());
}
}
但是在这里您必须明确添加您需要的所有默认消息转换器。