本篇主要讲解RestTemplate的基本使用,它是Spring提供的用来访问Rest服务的客户端,RestTmplate提供了很多便捷的方法,可以大大提供开发效率,本篇只涉及基本使用,内部原理后续再展开
RestTemplate是Spring提供的用于发送HTTP请求的客户端工具,它遵循Restful原则,RestTemplate默认依赖JDK的Http连接工具HttpUrlConnection,你也可以替换不同的源,比如OkHttp、Apache HttpComponents 等等。。
在说RestTemplate之前,先介绍HttpMessageConverter,RestTemplate默认使用的转化HttpMessageConverter去将Http消息转换成POJO 或者 POJO转化成Http消息。在创建RestTemplate的时候会默认添加一组HttpMessageConveter的实现。
HttpMessageConverter源码:
public interface HttpMessageConverter<T> { //指示此转换器是否可以读取给定的类。 boolean canRead(Class<?> clazz, @Nullable MediaType mediaType); //指示此转换器是否可以写给定的类。 boolean canWrite(Class<?> clazz, @Nullable MediaType mediaType); //返回List<MediaType> List<MediaType> getSupportedMediaTypes(); //读取一个inputMessage T read(Class<? extends T> clazz, HttpInputMessage inputMessage) throws IOException, HttpMessageNotReadableException; //往output message写一个Object void write(T t, @Nullable MediaType contentType, HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException; }
RestTemplate中如何添加HttpMessageConverter的
构造器源码:
static { ClassLoader classLoader = RestTemplate.class.getClassLoader(); romePresent = ClassUtils.isPresent("com.rometools.rome.feed.WireFeed", classLoader); jaxb2Present = ClassUtils.isPresent("javax.xml.bind.Binder", classLoader); jackson2Present = ClassUtils.isPresent("com.fasterxml.jackson.databind.ObjectMapper", classLoader) && ClassUtils.isPresent("com.fasterxml.jackson.core.JsonGenerator", classLoader); jackson2XmlPresent = ClassUtils.isPresent("com.fasterxml.jackson.dataformat.xml.XmlMapper", classLoader); jackson2SmilePresent = ClassUtils.isPresent("com.fasterxml.jackson.dataformat.smile.SmileFactory", classLoader); jackson2CborPresent = ClassUtils.isPresent("com.fasterxml.jackson.dataformat.cbor.CBORFactory", classLoader); gsonPresent = ClassUtils.isPresent("com.google.gson.Gson", classLoader); jsonbPresent = ClassUtils.isPresent("javax.json.bind.Jsonb", classLoader); } public RestTemplate() { this.messageConverters.add(new ByteArrayHttpMessageConverter()); this.messageConverters.add(new StringHttpMessageConverter()); this.messageConverters.add(new ResourceHttpMessageConverter(false)); try { this.messageConverters.add(new SourceHttpMessageConverter<>()); } catch (Error err) { // Ignore when no TransformerFactory implementation is available } this.messageConverters.add(new AllEncompassingFormHttpMessageConverter()); if (romePresent) { this.messageConverters.add(new AtomFeedHttpMessageConverter()); this.messageConverters.add(new RssChannelHttpMessageConverter()); } if (jackson2XmlPresent) { this.messageConverters.add(new MappingJackson2XmlHttpMessageConverter()); } else if (jaxb2Present) { this.messageConverters.add(new Jaxb2RootElementHttpMessageConverter()); } if (jackson2Present) { this.messageConverters.add(new MappingJackson2HttpMessageConverter()); } else if (gsonPresent) { this.messageConverters.add(new GsonHttpMessageConverter()); } else if (jsonbPresent) { this.messageConverters.add(new JsonbHttpMessageConverter()); } if (jackson2SmilePresent) { this.messageConverters.add(new MappingJackson2SmileHttpMessageConverter()); } if (jackson2CborPresent) { this.messageConverters.add(new MappingJackson2CborHttpMessageConverter()); } this.uriTemplateHandler = initUriTemplateHandler(); }
从RestTemplate的构造器源码中我们可以看到构造方法中 根据ClassUtils.isPresent判断当前项目是否存在某些jar包向RestTemplate中添加不同的 HttpMessageConverter实现,Spring默认会添加 StringHttpMessageConverter , MappingJackson2XmlHttpMessageConverter等等
首先来看Get请求 RestTemplate提供了2种方法其中一种就是 getForObject()方法
public <T> T getForObject(String url, Class<T> responseType, Object... uriVariables){} public <T> T getForObject(String url, Class<T> responseType, Map<String, ?> uriVariables) public <T> T getForObject(URI url, Class<T> responseType)
客户端 String url = "http://localhost:9999/testGetMethod"; String str = restTemplate.getForObject(url , String.class);、 服务端 @RequestMapping("/testGetMethod") public String testGetMethod(){ return "hello"; }
客户端 String url = "http://localhost:9999/testGetMethod/{talk}/{name}"; //或者testGetMethod/{1}/{2} {里面的参数无所谓,只是根据下面的Object... uriVariables 逐一绑定到上面{} 中去的} String str = restTemplate.getForObject(url , String.class,"hello" , "johnny"); 服务端 @RequestMapping("/testGetMethod/{talk}/{name}") public String testGetMethod(@PathVariable("talk") String talk , @PathVariable("name") String name){ log.info("【{} : {}】" , talk , name); return "hello"; }
说明{} http://localhost :9999/testGetMethod/{talk}/{name} 里面的参数名称无所谓 ,只是根据下面的Object... uriVariables 逐一绑上去的, 具体绑定源码请看 DefaultUriBuilderFactory的fromUriString方法内部是根据正则表达式进行绑定的 ,最终将返回 URI,URI的string属性 就是绑定后要访问的路径
//不早了 先写这么多吧 明天把下面的补齐 ,先去睡觉了!!!
//继续补齐。。
String url = "http://localhost:9999/testGetMethod/{talk}/{name}"; Map<String,String> map = new HashMap<>(); map.put("talk" , "hello"); map.put("name" , "johnny"); String str = restTemplate.getForObject(url , String.class,map);
可以看出来是通过Map绑定参数的,这个和上面不一样的是 map的key 一定要和 url中 {} 中的 保持一致 ,如果不一致会报错
String url = "http://localhost:9999/testGetMethod/{talk}/{name}"; map.put("talk2" , "hello");
源码
RestTemplate 提供的Get请求的第二种方法 ,基本和getForObject一致 ,就是返回类型不同,它是在getForObject返回的基础上再包装了一层 ResponseEntity 用于包含Http请求的全部信息
public <T> ResponseEntity<T> getForEntity(String url, Class<T> responseType, Object... uriVariables){} public <T> ResponseEntity<T> getForEntity(String url, Class<T> responseType, Map<String, ?> uriVariables){} public <T> ResponseEntity<T> getForEntity(URI url, Class<T> responseType){}
String url = "http://localhost:9999/testGetMethodForEntity/"; ResponseEntity<Student> responseEntity = restTemplate.getForEntity(url , Student.class); responseEntity.getStatusCode(); responseEntity.getHeaders(); responseEntity.getBody(); log.info("【responseEntity : {}】" , responseEntity);
String url = "http://localhost:9999/testGetMethodForEntity/{name}/{age}"; ResponseEntity<Student> responseEntity = restTemplate.getForEntity(url , Student.class , "johnny" , "23"); log.info("【responseEntity : {}】" , responseEntity);
String url = "http://localhost:9999/testGetMethodForEntity/{name}/{age}"; Map<String,String> map = new HashMap<>(); map.put("name","johnny"); map.put("age" , "23"); ResponseEntity<Student> responseEntity = restTemplate.getForEntity(url , Student.class ,"map"); log.info("【responseEntity : {}】" , responseEntity);
**但是,通常情况下我们并不想要Http请求的全部信息,只需要相应体即可.对于这种情况,RestTemplate提供了 getForObject() 方法用来只获取 响应体信息.
getForObject 和 getForEntity 用法几乎相同,指示返回值返回的是 响应体,省去了我们 再去 getBody() .**
public <T> T postForObject(String url, @Nullable Object request, Class<T> responseType, Object... uriVariables) throws RestClientException {} public <T> T postForObject(String url, @Nullable Object request, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException {} public <T> T postForObject(URI url, @Nullable Object request, Class<T> responseType) throws RestClientException {}
客户端代码: String url = "http://localhost:9999/testPostMethodForObject"; Student student = new Student(); student.setName("johnny"); student.setAge("23"); String msg = restTemplate.postForObject(url , student , String.class); 服务端代码: @RequestMapping("/testPostMethodForObject") public String testGetMethodForEntity(@RequestBody Student student){ log.info("【studeng: {}】" , student); return "success"; }
public <T> T postForObject(String url, @Nullable Object request, Class<T> responseType, Object... uriVariables) throws RestClientException {} public <T> T postForObject(String url, @Nullable Object request, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException {} public <T> T postForObject(URI url, @Nullable Object request, Class<T> responseType) throws RestClientException {}
@RequestMapping("/testPostMethodForEntity") public void testPostMethodForEntity(){ String url = "http://localhost:9999/testPostMethodForEntity"; Student student = new Student(); student.setName("johnny"); student.setAge("23"); ResponseEntity<String> responseEntity = restTemplate.postForEntity(url , student , String.class); log.info(responseEntity.getBody()); }
可以看出来postForEntity和postForObject 几乎一样。
唯有 ResponseExtractor<T> 不同
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