Spring：如何在运行时选择响应类型？

2019年8月6日 265次阅读

我想在方法中选择运行时的响应媒体类型.

例如,以下代码：

@RequestMapping(value = "/getRecord",
    produces = {"application/octet-stream", "application/json;charset=UTF-8" })
public byte[] getData(
    @RequestParam(value="id", required=true) Integer id)
    throws IOException
{
    if (id == 1)
        return createByteArray();
    throw new MyDataException();
}

在此代码中,可能的响应类型实际上是2.

> byte [](按正常执行路径)
> MyDataException(由异常执行路径)

MyDataException稍后由异常处理程序处理,并转换为简单类.它可以转换为json响应.

首先,我认为如果我为@RequestMapping注释的产生选项提供2种响应类型,则消息转换器将根据实际返回对象转换2种类型.但事实并非如此.

在spring类org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor中,如果存在produce选项,则writeWithMessageConverters()方法在选择响应类型时忽略实际的返回对象类型.

如何让Spring根据实际的返回对象在运行时选择响应类型？

最佳答案 另一种可能性是两种所述解决方案之间的混合方法：

@ControllerAdvice
public class MyExceptionHandler extends ResponseEntityExceptionHandler {

@ExceptionHandler({ MyDataException.class })
protected ResponseEntity<Object> handleInvalidRequest(RuntimeException e, WebRequest request) {
    MyDataExceptionire = (MyDataException) e;
    List<FieldErrorResource> fieldErrorResources = new ArrayList<>();

    List<FieldError> fieldErrors = ire.getErrors().getFieldErrors();
    for (FieldError fieldError : fieldErrors) {
        FieldErrorResource fieldErrorResource = new FieldErrorResource();
        fieldErrorResource.setResource(fieldError.getObjectName());
        fieldErrorResource.setField(fieldError.getField());
        fieldErrorResource.setCode(fieldError.getCode());
        fieldErrorResource.setMessage(fieldError.getDefaultMessage());
        fieldErrorResources.add(fieldErrorResource);
    }

    ErrorResource error = new ErrorResource("MyDataException", ire.getMessage());
    error.setFieldErrors(fieldErrorResources);

    HttpHeaders headers = new HttpHeaders();
    headers.setContentType(MediaType.APPLICATION_JSON);

    return handleExceptionInternal(e, error, headers, HttpStatus.UNPROCESSABLE_ENTITY, request);
}}

解决方案于this blog提出

编辑：

我还从博客中添加了FieldError和ErrorResource类,因为它将来可能会被删除：

ErrorResource：

@JsonIgnoreProperties(ignoreUnknown = true)
public class ErrorResource {
private String code;
private String message;
private List<FieldErrorResource> fieldErrors;

public ErrorResource() { }

public ErrorResource(String code, String message) {
    this.code = code;
    this.message = message;
}

public String getCode() { return code; }

public void setCode(String code) { this.code = code; }

public String getMessage() { return message; }

public void setMessage(String message) { this.message = message; }

public List<FieldErrorResource> getFieldErrors() { return fieldErrors; }

public void setFieldErrors(List<FieldErrorResource> fieldErrors) {
    this.fieldErrors = fieldErrors;
}
}

FieldErrorResource：

@JsonIgnoreProperties(ignoreUnknown = true)
public class FieldErrorResource {
private String resource;
private String field;
private String code;
private String message;

public String getResource() { return resource; }

public void setResource(String resource) { this.resource = resource; }

public String getField() { return field; }

public void setField(String field) { this.field = field; }

public String getCode() { return code; }

public void setCode(String code) { this.code = code; }

public String getMessage() { return message; }

public void setMessage(String message) { this.message = message; }}
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