框架版本
springboot 2.2.1.RELEASE
fastjson 1.2.78
maven pom.xml parent 和 dependencies
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.2.1.RELEASE</version>
</parent>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.18.12</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-websocket</artifactId>
</dependency>
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>fastjson</artifactId>
<version>1.2.78</version>
</dependency>
</dependencies>
问题
如下代码，返回结果是 "hello world"，添加了一个双引号。
@RestController
@Slf4j
public class Hello1Controller {
@GetMapping(value = "/printHello")
@ResponseBody
public String printHello() {
return "hello world";
}
}
排查
不管返回什么的结果，肯定经过MessageConvert进行消息的输出，debug看使用了哪一个MessageConvert
选择MessageConvert的方法是
org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor#writeWithMessageConverters(T, org.springframework.core.MethodParameter, org.springframework.http.server.ServletServerHttpRequest, org.springframework.http.server.ServletServerHttpResponse)
关键代码
if (selectedMediaType != null) {
selectedMediaType = selectedMediaType.removeQualityValue();
// 打个断点在此处
for (HttpMessageConverter<?> converter : this.messageConverters) {
GenericHttpMessageConverter genericConverter = (converter instanceof GenericHttpMessageConverter ?
(GenericHttpMessageConverter<?>) converter : null);
if (genericConverter != null ?
((GenericHttpMessageConverter) converter).canWrite(targetType, valueType, selectedMediaType) :
converter.canWrite(valueType, selectedMediaType)) {
body = getAdvice().beforeBodyWrite(body, returnType, selectedMediaType,
(Class<? extends HttpMessageConverter<?>>) converter.getClass(),
inputMessage, outputMessage);
if (body != null) {
Object theBody = body;
LogFormatUtils.traceDebug(logger, traceOn ->
"Writing [" + LogFormatUtils.formatValue(theBody, !traceOn) + "]");
addContentDispositionHeader(inputMessage, outputMessage);
if (genericConverter != null) {
genericConverter.write(body, targetType, selectedMediaType, outputMessage);
}
else {
((HttpMessageConverter) converter).write(body, selectedMediaType, outputMessage);
}
}
else {
if (logger.isDebugEnabled()) {
logger.debug("Nothing to write: null body");
}
}
return;
}
}
}
debug发现我的messageConvert只有一个，是com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter。那肯定是经过FastJson将String 写到输出流。
debug查看FastJsonHttpMessageConverter具体的write 代码 ，可以看到此时输出字符串添加了引号。
方法：com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter#writeInternal
写个fastjson 转化字符串试试，如下结果输出是 "hello world"，添加了引号。
import com.alibaba.fastjson.JSON;
public class JsonTest {
public static void main(String[] args) {
System.out.println(JSON.toJSONString("hello world"));
//
}
}
问题所在
import com.alibaba.fastjson.serializer.SerializerFeature;
import com.alibaba.fastjson.support.config.FastJsonConfig;
import com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.MediaType;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
import java.math.RoundingMode;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.List;
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
FastJsonHttpMessageConverter fastJsonConverter = new FastJsonHttpMessageConverter();
FastJsonConfig config = new FastJsonConfig();
config.setCharset(StandardCharsets.UTF_8);
//设置允许返回为null的属性
config.setSerializerFeatures(SerializerFeature.WriteMapNullValue);
fastJsonConverter.setFastJsonConfig(config);
List<MediaType> list = new ArrayList<>();
list.add(MediaType.APPLICATION_JSON);
fastJsonConverter.setSupportedMediaTypes(list);
converters.add(fastJsonConverter);
}
}
我配置了FastJsonHttpMessageConverter ，导致只使用FastJsonHttpMessageConverter 进行消息转换。
解决方法
添加StringHttpMessageConverter ，让其转化String。注意顺序，StringHttpMessageConverter 要在FastJsonHttpMessageConverter 之前。
@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
FastJsonHttpMessageConverter fastJsonConverter = new FastJsonHttpMessageConverter();
FastJsonConfig config = new FastJsonConfig();
config.setCharset(StandardCharsets.UTF_8);
//设置允许返回为null的属性
config.setSerializerFeatures(SerializerFeature.WriteMapNullValue);
fastJsonConverter.setFastJsonConfig(config);
List<MediaType> list = new ArrayList<>();
list.add(MediaType.APPLICATION_JSON);
fastJsonConverter.setSupportedMediaTypes(list);
StringHttpMessageConverter stringHttpMessageConverter = new StringHttpMessageConverter();
stringHttpMessageConverter.setSupportedMediaTypes(list);
converters.add(stringHttpMessageConverter);
converters.add(fastJsonConverter);
}
返回数据没有引号了。
参考资料
【Spring】HttpMessageConverter的作用及替换
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