初探RestTemplate--解决中文乱码问题

女爷i 2022-05-19 23:16 394阅读 0赞

本文完全承接上一篇文章：[初探RestTemplate--postForObject方法直接传递对象][RestTemplate--postForObject]，如果你还没有看过，建议先阅读完再看下去。如果你没有兴趣也可以直接拉到本文末尾，查看我对中文乱码的解决方案。

我们在TestController中添加一个新的方法用来接收JSON格式的字符串

@RequestMapping(value = "/string", method = RequestMethod.POST)
    public String postByJsonString(@RequestBody String jsonString) {
        if (jsonString == null || "".equals(jsonString)) {
            return "FAIL";
        }
        return "SUCCESS:" + jsonString;
    }

然后在单元测试类ResttemplateApplicationTests中新增测试方法

@Test
    public void testString() {
        JSONObject json = new JSONObject();
        json.put("age", 18);
        json.put("name", "小芳");
        json.put("address", "广东深圳");
        RestTemplate restTemplate = RestTemplateUtil.getInstance("utf-8");
        String url = "http://localhost:9999/test/string";
        String result = restTemplate.postForObject(url, json.toJSONString(), String.class);
        System.out.println(result);
    }

单独跑testString方法，意外产生了

"D:\Program Files\Java\jdk1.8.0_121\bin\java" -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:14875,suspend=y,server=n -ea -Didea.test.cyclic.buffer.size=1048576 -Dfile.encoding=UTF-8 -classpath "D:\Program Files\JetBrains\IntelliJ IDEA 2017.2.6\lib\idea_rt.jar;D:\Program Files\JetBrains\IntelliJ IDEA 2017.2.6\plugins\junit\lib\junit-rt.jar;D:\Program Files\JetBrains\IntelliJ IDEA 2017.2.6\plugins\junit\lib\junit5-rt.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\charsets.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\deploy.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\access-bridge-64.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\cldrdata.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\dnsns.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\jaccess.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\jfxrt.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\localedata.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\nashorn.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\sunec.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\sunjce_provider.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\sunmscapi.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\sunpkcs11.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\zipfs.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\javaws.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\jce.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\jfr.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\jfxswt.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\jsse.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\management-agent.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\plugin.jar;D:\Program Files\Java\jdk1.8.0_121\jre\lib\resources.jar;D:\Program 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in\external\google\android-json\0.0.20131108.vaadin1\android-json-0.0.20131108.vaadin1.jar;C:\Users\usher\.m2\repository\org\springframework\spring-core\4.3.11.RELEASE\spring-core-4.3.11.RELEASE.jar;C:\Users\usher\.m2\repository\org\springframework\spring-test\4.3.11.RELEASE\spring-test-4.3.11.RELEASE.jar;C:\Users\usher\.m2\repository\commons-codec\commons-codec\1.10\commons-codec-1.10.jar;C:\Users\usher\.m2\repository\org\apache\commons\commons-lang3\3.6\commons-lang3-3.6.jar;C:\Users\usher\.m2\repository\com\google\guava\guava\23.0\guava-23.0.jar;C:\Users\usher\.m2\repository\com\google\code\findbugs\jsr305\1.3.9\jsr305-1.3.9.jar;C:\Users\usher\.m2\repository\com\google\errorprone\error_prone_annotations\2.0.18\error_prone_annotations-2.0.18.jar;C:\Users\usher\.m2\repository\com\google\j2objc\j2objc-annotations\1.1\j2objc-annotations-1.1.jar;C:\Users\usher\.m2\repository\org\codehaus\mojo\animal-sniffer-annotations\1.14\animal-sniffer-annotations-1.14.jar;C:\Users\usher\.m2\repository\mysql\mysql-connector-java\5.1.44\mysql-connector-java-5.1.44.jar;C:\Users\usher\.m2\repository\org\mybatis\mybatis-spring\1.3.1\mybatis-spring-1.3.1.jar;C:\Users\usher\.m2\repository\org\mybatis\mybatis\3.4.5\mybatis-3.4.5.jar;C:\Users\usher\.m2\repository\tk\mybatis\mapper\3.4.2\mapper-3.4.2.jar;C:\Users\usher\.m2\repository\javax\persistence\persistence-api\1.0\persistence-api-1.0.jar;C:\Users\usher\.m2\repository\com\github\pagehelper\pagehelper\4.2.1\pagehelper-4.2.1.jar;C:\Users\usher\.m2\repository\com\github\jsqlparser\jsqlparser\0.9.5\jsqlparser-0.9.5.jar;C:\Users\usher\.m2\repository\com\alibaba\fastjson\1.2.39\fastjson-1.2.39.jar;C:\Users\usher\.m2\repository\com\alibaba\druid-spring-boot-starter\1.1.4\druid-spring-boot-starter-1.1.4.jar;C:\Users\usher\.m2\repository\com\alibaba\druid\1.1.4\druid-1.1.4.jar;D:\Program Files\Java\jdk1.8.0_121\lib\jconsole.jar;D:\Program Files\Java\jdk1.8.0_121\lib\tools.jar;C:\Users\usher\.m2\repository\org\springframework\boot\spring-boot-autoconfigure\1.5.7.RELEASE\spring-boot-autoconfigure-1.5.7.RELEASE.jar;C:\Users\usher\.m2\repository\org\freemarker\freemarker\2.3.23\freemarker-2.3.23.jar;C:\Users\usher\.m2\repository\org\mybatis\generator\mybatis-generator-core\1.3.5\mybatis-generator-core-1.3.5.jar" com.intellij.rt.execution.junit.JUnitStarter -ideVersion5 -junit4 com.conpany.project.ResttemplateApplicationTests,testString
    Connected to the target VM, address: '127.0.0.1:14875', transport: 'socket'
    21:57:09.155 [main] DEBUG org.springframework.web.client.RestTemplate - Created POST request for "http://localhost:9999/test/string"
    21:57:09.158 [main] DEBUG org.springframework.web.client.RestTemplate - Setting request Accept header to [text/plain, application/json, application/*+json, text/plain, */*, */*]
    21:57:09.159 [main] DEBUG org.springframework.web.client.RestTemplate - Writing [{"address":"广东深圳","name":"小芳","age":18}] using [org.springframework.http.converter.StringHttpMessageConverter@20b2475a]
    21:57:09.440 [main] DEBUG org.springframework.web.client.RestTemplate - POST request for "http://localhost:9999/test/string" resulted in 200 (null)
    21:57:09.441 [main] DEBUG org.springframework.web.client.RestTemplate - Reading [java.lang.String] as "text/plain;charset=UTF-8" using [org.springframework.http.converter.StringHttpMessageConverter@20b2475a]
    Disconnected from the target VM, address: '127.0.0.1:14875', transport: 'socket'
    "SUCCESS:{\"address\":\"????\",\"name\":\"??\",\"age\":18}""SUCCESS:{\"address\":\"????\",\"name\":\"??\",\"age\":18}"

控制台的输入竟然是乱码，这很让人意外，因为上篇文章的测试结果均未出现乱码！

通过跟踪断点，简单分析下RestTemplate内部源码，发现上篇文章以JavaBean，Map，JSONObject格式分别提交数据时，postForObject底层均采用了MappingJackson2HttpMessageConverter来处理请求。而本文以String格式提交数据时，底层其实采用的是StringHttpMessageConverter来处理请求。

所以我们工具类中getInstance方法貌似创建了指定字符集的RestTemplate对象，实则并非如此，这个工具类并不靠谱，一定是我们的getInstance方法出了问题！

查看RestTemplate构造器如下：

![70][]

而StringHttpMessageConverter构造器约定了其默认字符集是ISO-8859-1

![70 1][]

回顾我们的getInstance方法创建对象的方式：

public static RestTemplate getInstance(String charset) {
        RestTemplate restTemplate = new RestTemplate();
        restTemplate.getMessageConverters().add(new StringHttpMessageConverter(Charset.forName(charset)));
        return restTemplate;
    }

这种方式并不靠谱，因为它首先调用了RestTemplate的构造器，这个构造器已经创建了一个默认字符集为ISO-8859-1的StringHttpMessageConverter对象。我们的getInstance 方法只是新增了一个指定字符集的StringHttpMessageConverter而非覆盖，所以提交String格式的post请求使用的字符集仍然是ISO-8859-1。

继续走查源码，发现所有的HttpMessageConverter对象均存放于messageConverters这个集合里面，很清楚的看出来它是个不可变的有序集合ArrrayList。

![70 2][]

所以我们对于任何HttpMessageConverter的修改都不应该改变其内在的顺序。

故一方面要保证集合messageConverters中只有一个StringHttpMessageConverter对象，另一方面要保证该对象位置不被改变。我们可以将getInstance方法改造成如下的形式：

public static RestTemplate getInstance(String charset) {
        RestTemplate restTemplate = new RestTemplate();
        List<HttpMessageConverter<?>> list = restTemplate.getMessageConverters();
        for (HttpMessageConverter<?> httpMessageConverter : list) {
            if(httpMessageConverter instanceof StringHttpMessageConverter) {
                ((StringHttpMessageConverter) httpMessageConverter).setDefaultCharset(Charset.forName(charset));
                break;
            }
        }
        return restTemplate;
    }

经过测试，控制台未出现乱码，问题解决。谢谢观看，欢迎指正，若有不足，请不吝赐教。

[RestTemplate--postForObject]: https://mp.csdn.net/postedit/80955558
[70]: /images/20220520/3723b6d8c074495ebb230b4b247bc472.png
[70 1]: /images/20220520/5742c8ea2fe64367bff5018a5780967c.png
[70 2]: /images/20220520/63e8a20e305e414e9c9c6f596ef93b50.png