SpringBoot響應處理實現流程詳解

<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-json</artifactId>
	<version>2.7.0</version>
	<scope>compile</scope>
</dependency>

<dependency>
  <groupId>com.fasterxml.jackson.core</groupId>
  <artifactId>jackson-databind</artifactId>
  <version>2.13.3</version>
  <scope>compile</scope>
</dependency>
<dependency>
  <groupId>com.fasterxml.jackson.datatype</groupId>
  <artifactId>jackson-datatype-jdk8</artifactId>
  <version>2.13.3</version>
  <scope>compile</scope>
</dependency>
<dependency>
  <groupId>com.fasterxml.jackson.datatype</groupId>
  <artifactId>jackson-datatype-jsr310</artifactId>
  <version>2.13.3</version>
  <scope>compile</scope>
</dependency>

package org.springframework.web.method.support;
import org.springframework.core.MethodParameter;
import org.springframework.lang.Nullable;
import org.springframework.web.context.request.NativeWebRequest;
public interface HandlerMethodReturnValueHandler {
    boolean supportsReturnType(MethodParameter returnType);
    void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType, ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception;
}

public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType, ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
	// 獲取自己適合的返回值解析器
    HandlerMethodReturnValueHandler handler = this.selectHandler(returnValue, returnType);
    if (handler == null) {
        throw new IllegalArgumentException("Unknown return value type: " + returnType.getParameterType().getName());
    } else {
    	// 呼叫該返回值解析器中的處理返回值的方法
        handler.handleReturnValue(returnValue, returnType, mavContainer, webRequest);
    }
}
@Nullable
private HandlerMethodReturnValueHandler selectHandler(@Nullable Object value, MethodParameter returnType) {
	// 判斷是否是非同步的返回值
    boolean isAsyncValue = this.isAsyncReturnValue(value, returnType);
    Iterator var4 = this.returnValueHandlers.iterator();
    HandlerMethodReturnValueHandler handler;
    // 使用do-while進行遍歷，找出支援當前返回值型別的解析器
    do {
        do {
            if (!var4.hasNext()) {
                return null;
            }

            handler = (HandlerMethodReturnValueHandler)var4.next();
        } while(isAsyncValue && !(handler instanceof AsyncHandlerMethodReturnValueHandler));
    } while(!handler.supportsReturnType(returnType));
    return handler;
}

public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType, ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {
	mavContainer.setRequestHandled(true);
	// 建立輸入和輸出資訊
	ServletServerHttpRequest inputMessage = this.createInputMessage(webRequest);
	ServletServerHttpResponse outputMessage = this.createOutputMessage(webRequest);
	// 使用訊息轉換器進行寫出操作
	this.writeWithMessageConverters(returnValue, returnType, inputMessage, outputMessage);
}

package org.springframework.http.converter;
import java.io.IOException;
import java.util.Collections;
import java.util.List;
import org.springframework.http.HttpInputMessage;
import org.springframework.http.HttpOutputMessage;
import org.springframework.http.MediaType;
import org.springframework.lang.Nullable;
public interface HttpMessageConverter<T> {
	// 讀取，將我們當前訊息轉換器支援的物件以某種格式讀取進來，例如將json資料讀取成Person物件
    boolean canRead(Class<?> clazz, @Nullable MediaType mediaType);
	// 寫出，我們當前訊息轉換器支援的物件以某種格式寫出去，例如將Person物件以json格式寫出去
    boolean canWrite(Class<?> clazz, @Nullable MediaType mediaType);
    List<MediaType> getSupportedMediaTypes();
    default List<MediaType> getSupportedMediaTypes(Class<?> clazz) {
        return !this.canRead(clazz, (MediaType)null) && !this.canWrite(clazz, (MediaType)null) ? Collections.emptyList() : this.getSupportedMediaTypes();
    }
    T read(Class<? extends T> clazz, HttpInputMessage inputMessage) throws IOException, HttpMessageNotReadableException;
    void write(T t, @Nullable MediaType contentType, HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException;
}

<dependency>
	<groupId>com.fasterxml.jackson.dataformat</groupId>
	<artifactId>jackson-dataformat-xml</artifactId>
</dependency>