原因
最近在写一些小的Demo案例，但是被AJAX的 json 返回乱码折磨了好久。最后通过研究StringHttpMessageConverter源代码发现，开发者很坑的使用了”ISO-8859-1”作为默认编码。经过代码测试，下面给出四种方法解决SpringMVC 返回 json 字符串中文乱码。（本文spring版本4.3.11.RELEASE）
public class StringHttpMessageConverter extends AbstractHttpMessageConverter<String> {public static final Charset DEFAULT_CHARSET = Charset.forName("ISO-8859-1");private volatile List<Charset> availableCharsets;private boolean writeAcceptCharset;// 后面省略
方法一：自己编写一个工具类
学过servlet我们可以知道，可以通过HttpServletResponse设置返回编码。
工具类
public class ResponseTool {public static void write(HttpServletResponse response,Object o)throws Exception{response.setContentType("text/html;charset=utf-8");PrintWriter out=response.getWriter();out.println(o.toString());out.flush();out.close();}}
测试方法
@RequestMapping(value = "/toolToJson")public void toolToJson(HttpServletResponse response) throws Exception {Map map = new HashMap();map.put("code", "200");map.put("msg", "这是一句话，测试返回json是否乱码。");ResponseTool.write(response,new Gson().toJson(map));}
方法二：使用produces属性
在RequestMapping使用（produces = “text/html; charset=utf-8”）produces 作用根据请求头中的Accept进行匹配，如请求头“Accept:text/html”时即可匹配。
如果类型是：application/json ，设置为：produces = “application/json; charset=utf-8”
测试方法
@RequestMapping(value = "/producesToJson", method = RequestMethod.GET, produces="text/html;charset=UTF-8")@ResponseBodypublic String producesToJson() {Map map = new HashMap();map.put("code", "200");map.put("msg", "这是一句话，测试返回json是否乱码。");return new Gson().toJson(map);}
方法三：通过配置spring-mvc.xml
在spring-mvc.xml添加配置
<mvc:annotation-driven><mvc:message-converters register-defaults="true"><bean class="org.springframework.http.converter.StringHttpMessageConverter"><property name="supportedMediaTypes"><list><value>text/html;charset=UTF-8</value><value>application/json;charset=UTF-8</value><value>text/plain;charset=UTF-8</value><value>application/xml;charset=UTF-8</value></list></property></bean></mvc:message-converters></mvc:annotation-driven>
测试方法
@RequestMapping(value = "/json")@ResponseBodypublic String json() {Map map = new HashMap();map.put("code", "200");map.put("msg", "这是一句话，测试返回json是否乱码。");return new Gson().toJson(map);}
方法四：完成自己的AbstractHttpMessageConverter
分析源码可以看出StringHttpMessageConverter继承与AbstractHttpMessageConverter，分析该抽象类得，相关的操作字符编码的方法可以重写，于是我们可以自定义一个类继承StringHttpMessageConverter，然后重写相关的方法。这里我们只需要把ISO-8859-1改成UTF-8，并修改构造方法。
UTF8StringHttpMessageConverter 类
package com.javazhan.controller;import org.springframework.http.HttpInputMessage;import org.springframework.http.HttpOutputMessage;import org.springframework.http.MediaType;import org.springframework.http.converter.AbstractHttpMessageConverter;import org.springframework.http.converter.HttpMessageNotReadableException;import org.springframework.http.converter.HttpMessageNotWritableException;import org.springframework.util.StreamUtils;import java.io.IOException;import java.io.UnsupportedEncodingException;import java.nio.charset.Charset;import java.util.ArrayList;import java.util.List;/*** @Author: yandq* @Description:* @Date: Create in 11:50 /4/3* @Modified By:*/public class UTF8StringHttpMessageConverter extends AbstractHttpMessageConverter<String> {public static final Charset DEFAULT_CHARSET = Charset.forName("UTF-8");private volatile List<Charset> availableCharsets;private boolean writeAcceptCharset;public UTF8StringHttpMessageConverter() {this(DEFAULT_CHARSET);}public UTF8StringHttpMessageConverter(Charset defaultCharset) {super(defaultCharset, new MediaType[]{MediaType.TEXT_PLAIN, MediaType.ALL});this.writeAcceptCharset = true;}public void setWriteAcceptCharset(boolean writeAcceptCharset) {this.writeAcceptCharset = writeAcceptCharset;}@Overridepublic boolean supports(Class<?> clazz) {return String.class == clazz;}@Overrideprotected String readInternal(Class<? extends String> clazz, HttpInputMessage inputMessage) throws IOException {Charset charset = this.getContentTypeCharset(inputMessage.getHeaders().getContentType());return StreamUtils.copyToString(inputMessage.getBody(), charset);}@Overrideprotected Long getContentLength(String str, MediaType contentType) {Charset charset = this.getContentTypeCharset(contentType);try {return (long)str.getBytes(charset.name()).length;} catch (UnsupportedEncodingException var5) {throw new IllegalStateException(var5);}}@Overrideprotected void writeInternal(String str, HttpOutputMessage outputMessage) throws IOException {if (this.writeAcceptCharset) {outputMessage.getHeaders().setAcceptCharset(this.getAcceptedCharsets());}Charset charset = this.getContentTypeCharset(outputMessage.getHeaders().getContentType());StreamUtils.copy(str, charset, outputMessage.getBody());}protected List<Charset> getAcceptedCharsets() {if (this.availableCharsets == null) {this.availableCharsets = new ArrayList(Charset.availableCharsets().values());}return this.availableCharsets;}private Charset getContentTypeCharset(MediaType contentType) {return contentType != null && contentType.getCharset() != null ? contentType.getCharset() : this.getDefaultCharset();}}
定义好上面的类后，只需要将该类注册到Spring的annotaion 处理序列中即可，当加上@ResponseBody时，Spring将会调用上面自定义类中复写的方法，从而返回UTF-8的编码：
<mvc:annotation-driven><mvc:message-converters register-defaults="true"><bean class="com.javazhan.controller.UTF8StringHttpMessageConverter"/></mvc:message-converters></mvc:annotation-driven>
测试方法
@RequestMapping(value = "/json")@ResponseBodypublic String json() {Map map = new HashMap();map.put("code", "200");map.put("msg", "这是一句话，测试返回json是否乱码。");return new Gson().toJson(map);}
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