从零到一了解RestTemplate
一、RestTemplate是什么
RestTemplate是Spring用于同步client端的核心类,简化了与HTTP服务的通信,并满足RestFul原则,程序代码可以给它提供URL,并提取结果。默认情况下,RestTemplate默认依赖jdk的HTTP连接工具。当然你也可以通过setRequestFactory属性切换到不同的HTTP源,比如Apache HttpComponents、Netty和OkHttp。RestTemplate能大幅简化了提交表单的难度,并且附带了自动转换JSON数据的功能。
该类的入口主要根据HTTP的六个方法制定:
此外,exchange和excute可以通用上述方法。
在内部,RestTemplate默认使用HttpMessageConverter实例将HTTP消息转换成POJO或者从POJO转换成HTTP消息。默认情况下会注册主mime类型的转换器,但也可以用过setMessageConverters注册其他的转换器。
HttpMessageConverter.java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; }
在内部,RestTemplate默认使用SimpleClientHttpRequestFactory和DefaultResponseErrorHandler来分别处理HTTP的创建和错误,但也可以通过setRequestFactory和setErrorHandler来覆盖。
2、get请求
2.1.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)
getForObject()比getForEntity() 多包含了将HTTP转成POJO的功能,但是getForObject没有处理response能力。因为它拿到手的就是成型的pojo。省略了很多response信息。
POJO(Plain Ordinary Java Object):实体类,一般带有一些getter和setter方法(特点就是支持业务逻辑的协作类)
public class Notice{ private int status; private Object msg; private List<DataBean> data; } public class DataBean{ private int noticeId; private String noticeTitle; private Object noticeImg; private long noticeCreateTime; private long noticeUpdateTime; private String noticeContent; }
例子1:不带参的get请求
@test public void restTemplateGetTest(){ RestTemplate restTemplate = new RestTemplate(); Notice notice = testTemplate.getForObject("http://xxx.top/notice/list/1/5",Notice.class); System.out.println(notice); }
控制台打印:
INFO 19076 --- [ main] c.w.s.c.w.c.HelloControllerTest : Started HelloControllerTest in 5.532 seconds (JVM running for 7.233) Notice{status=200, msg=null, data=[DataBean{noticeId=21, noticeTitle='aaa', noticeImg=null, noticeCreateTime=1525292723000, noticeUpdateTime=1525292723000, noticeContent='<p>aaa</p>'}, DataBean{noticeId=20, noticeTitle='ahaha', noticeImg=null, noticeCreateTime=1525291492000, noticeUpdateTime=1525291492000, noticeContent='<p>ah.......'
例子2:带参数的get请求
Notice notice = restTemplate.getForObject("http://fantj.top/notice/list/{1}/{2}",Notice.class,1,5);
例子3:带参数的get请求2
Map<String,Sting> map = new HashMap(); map.put("start","1"); map.put("page","5"); Notice notice = restTemplate.getForObject("http://fantj.top/notice/list/",Notice.class,map);
getForEneity()方法
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){}
与上述getForObject()方法不同的是返回的是ResponseEntity对象,如果需要转换成pojo,还需要json工具类的引入,如FastJson或者Jackson等工具类
ResponseEntity、HttpStatus、BodyBuilder结构
ResponseEntity.java
public HttpStatus getStatusCode(){} public int getStatusCodeValue(){} public boolean equals(@Nullable Object other) {} public String toString() {} public static BodyBuilder status(HttpStatus status) {} public static BodyBuilder ok() {} public static <T> ResponseEntity<T> ok(T body) {} public static BodyBuilder created(URI location) {} ...
HttpStatus.java
public enum HttpStatus{ public boolean is1xxInformational(){} public boolean is2xxSuccessful(){} public boolean is3xxRedirection(){} public boolean is4xxClientError(){} public boolean is5xxServerError(){} public boolean isError(){} }
BodyBuilder.java
public interface BodyBuilder extends HeadersBuilder<BodyBuilder> { //设置正文的长度,以字节为单位,由Content-Length标头 BodyBuilder contentLength(long contentLength); //设置body的MediaType 类型 BodyBuilder contentType(MediaType contentType); //设置响应实体的主体并返回它。 <T> ResponseEntity<T> body(@Nullable T body); }
ResponseEntity包含了HttpStatus和BodyBuilder的这些信息,这更方便我们处理response原生的东西
对于post请求同样有postForObject和postForEntity
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 {}
用一个验证邮箱的接口测试
@Test public void rtPostObject(){ RestTemplate restTemplate = new RestTemplate(); String url = "http://47.xxx.xxx.96/register/checkEmail"; HttpHeaders headers = new HttpHeaders(); headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED); MultiValueMap<String, String> map= new LinkedMultiValueMap<>(); map.add("email", "844072586@qq.com"); HttpEntity<MultiValueMap<String, String>> request = new HttpEntity<>(map, headers); ResponseEntity<String> response = restTemplate.postForEntity( url, request , String.class ); System.out.println(response.getBody()); }
执行结果:
{"status":500,"msg":"该邮箱已被注册","data":null}
代码中MultiValueMap是Map的一个子类,它的一个key可以存储多个value
public interface MultiValueMap<K,V> extends Map<K,List<V>>{...}
为什么用MultiValueMap?因为HttpEntity接受的request类型是它。
public HttpEntity(@Nullable T body, @Nullable MultiValueMap<String, String> headers){} //我这里只展示它的一个construct,从它可以看到我们传入的map是请求体,headers是请求头。
为什么用HttpEntity是因为restTemplate.postForEntity方法虽然表面上接收的request是@Nullable Object request类型,但是你追踪下去会发现,这个request是用HttpEntity来解析。核心代码如下:
if (requestBody instanceof HttpEntity) { this.requestEntity = (HttpEntity<?>) requestBody; }else if (requestBody != null) { this.requestEntity = new HttpEntity<>(requestBody); }else { this.requestEntity = HttpEntity.EMPTY; }
使用exchange指定调用方式
exchange可以指定请求的HTTP类型
例子:
@Test public void rtExchangeTest() throws JSONException { RestTemplate restTemplate = new RestTemplate(); String url = "http://xxx.top/notice/list"; HttpHeaders headers = new HttpHeaders(); headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED); JSONObject jsonObj = new JSONObject(); jsonObj.put("start",1); jsonObj.put("page",5); HttpEntity<String> entity = new HttpEntity<>(jsonObj.toString(), headers); ResponseEntity<JSONObject> exchange = restTemplate.exchange(url, HttpMethod.GET, entity, JSONObject.class); System.out.println(exchange.getBody()); }
excute()指定调用方式
excute()的用法与exchange()大同小异了,它同样可以指定不同的HttpMethod,不同的是它返回的对象是响应体所映射成的对象,而不是ResponseEntity。
excute()方法是以上所有方法的底层调用
@Override @Nullable public <T> T postForObject(String url, @Nullable Object request, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException { RequestCallback requestCallback = httpEntityCallback(request, responseType); HttpMessageConverterExtractor<T> responseExtractor = new HttpMessageConverterExtractor<>(responseType, getMessageConverters(), logger); return execute(url, HttpMethod.POST, requestCallback, responseExtractor, uriVariables); }
参考:https://www.cnblogs.com/javazhiyin/p/9851775.html