标签：ade 定义 except utf-8 记录 ext handle city 自定义
Spring 系列目录(https://www.cnblogs.com/binarylei/p/10117436.html)
@GetMapping("/v1/{user_id}")
public User user(@PathVariable("user_id") String userId) {
return new User(userId, "binarylei", "123456");
}默认返回一个 json，如果需要返回 xml 或者自定义返回类型时怎么办呢？
<dependency>
<groupId>com.fasterxml.jackson.dataformat</groupId>
<artifactId>jackson-dataformat-xml</artifactId>
</dependency>(1) PropertiesHttpMessageConverter
public class PropertiesHttpMessageConverter extends AbstractHttpMessageConverter<User> {
public PropertiesHttpMessageConverter() {
super(Charset.forName("utf-8"), MediaType.valueOf("application/properties"));
}
@Override
protected boolean supports(Class clazz) {
return clazz == User.class;
}
@Override
protected User readInternal(Class<? extends User> clazz, HttpInputMessage inputMessage)
throws IOException, HttpMessageNotReadableException {
Properties properties = new Properties();
properties.load(inputMessage.getBody());
User user = new User();
user.setUserId(properties.getProperty("user.id"));
user.setUsername(properties.getProperty("user.name"));
return user;
}
@Override
protected void writeInternal(User user, HttpOutputMessage outputMessage)
throws IOException, HttpMessageNotWritableException {
Properties properties = new Properties();
properties.setProperty("user.id", user.getUserId());
properties.setProperty("user.name", user.getUsername());
properties.setProperty("user.password", user.getPassword());
properties.store(outputMessage.getBody(), "write");
}
}(2) 配置类 PropertiesWebMvcConfigurer
@Configuration
public class PropertiesWebMvcConfigurer implements WebMvcConfigurer {
@Override
public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
converters.add(new PropertiesHttpMessageConverter());
}
}(3) rest 接口定义
@GetMapping(value = "/v3/properties/to/json",
consumes = "application/properties",
produces = "application/json")
public User propertiesToHJson(@RequestBody User user) {
return new User("1", "binarylei", "123456");
}
@GetMapping(value = "/v3/json/to/properties",
consumes = "application/json",
produces = "application/properties")
public User jsonToProperties(@RequestBody User user) {
return new User("1", "binarylei", "123456");
}(4) 测试
请求地址：localhost:8080//v3/properties/to/json
请求头：Accept: application/properties, Content-Type: application/json
请求参数：user.id=1 user.name=binarylei请求地址：localhost:8080/v3/json/to/properties
请求头：Accept: application/json, Content-Type: application/properties
请求参数：{}@EnableWebMvc 注入了 DelegatingWebMvcConfiguration 组件，其类图结构如下：
在 WebMvcConfigurationSupport 类中定义了许多默认的 HttpMessageConverter，根据是否有相应的类加载来判断是否启动对应的 HttpMessageConverter。
// 类型转换器
private List<HttpMessageConverter<?>> messageConverters;
protected final List<HttpMessageConverter<?>> getMessageConverters() {
if (this.messageConverters == null) {
this.messageConverters = new ArrayList<>();
configureMessageConverters(this.messageConverters); // (1)
if (this.messageConverters.isEmpty()) {
addDefaultHttpMessageConverters(this.messageConverters); // (2)
}
extendMessageConverters(this.messageConverters); // (3)
}
return this.messageConverters;
}(1) 由子类 DelegatingWebMvcConfiguration 重写了 configureMessageConverters 方法，实际上是委托给了 WebMvcConfigurer 完成。
(2) 加载默认的 HttpMessageConverter
(3) 同 (1)，也是由子类重写 extendMessageConverters
下面我们看一下 Spring Boot 默认加载了那些 HttpMessageConverter
boolean jackson2Present = ClassUtils.isPresent("com.fasterxml.jackson.databind.ObjectMapper", classLoader) &&
ClassUtils.isPresent("com.fasterxml.jackson.core.JsonGenerator", classLoader);
boolean jackson2XmlPresent = ClassUtils.isPresent("com.fasterxml.jackson.dataformat.xml.XmlMapper", classLoader);
protected final void addDefaultHttpMessageConverters(List<HttpMessageConverter<?>> messageConverters) {
StringHttpMessageConverter stringHttpMessageConverter = new StringHttpMessageConverter();
stringHttpMessageConverter.setWriteAcceptCharset(false); // see SPR-7316
messageConverters.add(new ByteArrayHttpMessageConverter());
messageConverters.add(stringHttpMessageConverter);
messageConverters.add(new ResourceHttpMessageConverter());
messageConverters.add(new ResourceRegionHttpMessageConverter());
try {
messageConverters.add(new SourceHttpMessageConverter<>());
} catch (Throwable ex) {
// Ignore when no TransformerFactory implementation is available...
}
messageConverters.add(new AllEncompassingFormHttpMessageConverter());
// 省略...
if (jackson2XmlPresent) {
Jackson2ObjectMapperBuilder builder = Jackson2ObjectMapperBuilder.xml();
if (this.applicationContext != null) {
builder.applicationContext(this.applicationContext);
}
messageConverters.add(new MappingJackson2XmlHttpMessageConverter(builder.build()));
}
if (jackson2Present) {
Jackson2ObjectMapperBuilder builder = Jackson2ObjectMapperBuilder.json();
if (this.applicationContext != null) {
builder.applicationContext(this.applicationContext);
}
messageConverters.add(new MappingJackson2HttpMessageConverter(builder.build()));
}
// 省略...
}可以看到除了 ByteArrayHttpMessageConverter 等是固定加载外，其余的都是通过判断是否有相应的类来决定是否启用。如果需要使用相应的解析器，只需要到相应的 jar 包添加到 pom.xml 中即可。
最终容器中加载了如下的 HttpMessageConverter 解析器：
0 = {ByteArrayHttpMessageConverter@5783}
1 = {StringHttpMessageConverter@5784}
2 = {ResourceHttpMessageConverter@5785}
3 = {ResourceRegionHttpMessageConverter@5786}
4 = {SourceHttpMessageConverter@5787}
5 = {AllEncompassingFormHttpMessageConverter@5788}
6 = {MappingJackson2XmlHttpMessageConverter@5789}
7 = {MappingJackson2HttpMessageConverter@5790} 上文中提到 Spring Boot 启动时会在 messageConverters 集合中加载多个 HttpMessageConverter，到底执行那个呢？毫无疑问，执行肯定有三个过程：一是匹配对应的 HttpMessageConverter；二是执行 Handler；三是执行 HttpMessageConverter 响应结果。
HttpMessageConverter 的执行是在 AbstractMessageConverterMethodProcessor#writeWithMessageConverters 中执行的，这个方法很长，我们一点点来看。
MediaType selectedMediaType = null;
MediaType contentType = outputMessage.getHeaders().getContentType();
if (contentType != null && contentType.isConcrete()) {
selectedMediaType = contentType;
} else {
HttpServletRequest request = inputMessage.getServletRequest();
// 1. 获取客户端可接受的类型 Accept: application/jsion
List<MediaType> acceptableTypes = getAcceptableMediaTypes(request);
// 2. 服务端可以生成的所有 MediaType 类型
List<MediaType> producibleTypes = getProducibleMediaTypes(request, valueType, targetType);
if (body != null && producibleTypes.isEmpty()) {
throw new HttpMessageNotWritableException(
"No converter found for return value of type: " + valueType);
}
// 3. acceptableTypes 和 producibleTypes 比较，找出可用的 MediaType
List<MediaType> mediaTypesToUse = new ArrayList<>();
for (MediaType requestedType : acceptableTypes) {
for (MediaType producibleType : producibleTypes) {
if (requestedType.isCompatibleWith(producibleType)) {
mediaTypesToUse.add(getMostSpecificMediaType(requestedType, producibleType));
}
}
}
if (mediaTypesToUse.isEmpty()) {
if (body != null) {
throw new HttpMediaTypeNotAcceptableException(producibleTypes);
}
return;
}
MediaType.sortBySpecificityAndQuality(mediaTypesToUse);
// 4. 如果有多个 MediaType 可用，选择一个可用的返回
for (MediaType mediaType : mediaTypesToUse) {
// 只要是非 */* 就直接返回
if (mediaType.isConcrete()) {
selectedMediaType = mediaType;
break;
} else if (mediaType.equals(MediaType.ALL) || mediaType.equals(MEDIA_TYPE_APPLICATION)) {
selectedMediaType = MediaType.APPLICATION_OCTET_STREAM;
break;
}
}
}客户端可以传两个请求头过来：
Accept: application/xml // 客户端可接收的媒体类型
Content-Type: application/json // 客户端请求的媒体类型// 遍历 messageConverters，如果 converter 支持 selectedMediaType 则直接返回
for (HttpMessageConverter<?> converter : this.messageConverters) {
GenericHttpMessageConverter genericConverter = (converter instanceof GenericHttpMessageConverter ?
(GenericHttpMessageConverter<?>) converter : null);
// 1. canWrite 返回 true 则直接执行并结束循环
if (genericConverter != null ?
((GenericHttpMessageConverter) converter).canWrite(targetType, valueType, selectedMediaType) :
converter.canWrite(valueType, selectedMediaType)) {
// 2. 拿到 handler 的执行结果
body = getAdvice().beforeBodyWrite(body, returnType, selectedMediaType,
(Class<? extends HttpMessageConverter<?>>) converter.getClass(),
inputMessage, outputMessage);
if (body != null) {
Object theBody = body;
addContentDispositionHeader(inputMessage, outputMessage);
// 3. 执行对应的 genericConverter
if (genericConverter != null) {
genericConverter.write(body, targetType, selectedMediaType, outputMessage);
} else {
((HttpMessageConverter) converter).write(body, selectedMediaType, outputMessage);
}
}
return;
}
}核心的步骤 converter.write(body, selectedMediaType, outputMessage) 将 POJO 转换为 json 或 xml 后返回。
如果需要自定义 HttpMessageConverter，可以直接继承 AbstractHttpMessageConverter 类，重写 supports、readInternal、writeInternal 方法。
每天用心记录一点点。内容也许不重要，但习惯很重要！
标签：ade 定义 except utf-8 记录 ext handle city 自定义
原文地址：https://www.cnblogs.com/binarylei/p/10201762.html
