WebClient HTTP 请求问题处理模板（泛型响应、忽略 SSL 证书等）

一、请求大数据

1、问题案例

（1）Server

• 该接口返回一段大小为 1MB 的字符串

@GetMapping("/testBigData")publicStringtestBigData(){int targetSize =1024*1024;// 1MBStringBuilder sb =newStringBuilder(targetSize);for(int i =0; i < targetSize; i++)   sb.append('A');String largeString = sb.toString();return largeString;}

（2）Client

WebClient webClient =WebClient.create();Mono<String> response = webClient.get().uri("http://127.0.0.1:9999/test/testBigData").retrieve().bodyToMono(String.class);

response.subscribe(result ->{System.out.println("请求成功，结果长度为："+ result.length());}, throwable ->{
    throwable.printStackTrace();});

• 输出结果，因为数据量超过了设定的最大限制而报错

org.springframework.web.reactive.function.client.WebClientResponseException: 200 OK from GET http://127.0.0.1:9999/test/testBigData
Caused by: org.springframework.core.io.buffer.DataBufferLimitException: Exceeded limit on max bytes to buffer : 262144

2、处理策略

• 调整数据量的最大限制

int size =2*1024*1024;ExchangeStrategies strategies =ExchangeStrategies.builder().codecs(codecs -> codecs.defaultCodecs().maxInMemorySize(size)).build();WebClient webClient =WebClient.builder().exchangeStrategies(strategies).build();Mono<String> response = webClient.get().uri("http://127.0.0.1:9999/test/testBigData").retrieve().bodyToMono(String.class);

response.subscribe(result ->{System.out.println("请求成功，结果长度为："+ result.length());}, throwable ->{
    throwable.printStackTrace();});

二、不使用缓冲区请求图片

1、问题案例

（1）Server

• application.yaml

server:port:9999spring:mvc:static-path-pattern: /file/download/**web:resources:static-locations: file:D:/fileUpload/

（2）Client

WebClient webClient =WebClient.create();Mono<byte[]> response = webClient.get().uri("http://127.0.0.1:9999/file/download/1.png").accept(MediaType.IMAGE_JPEG,MediaType.IMAGE_PNG).retrieve().bodyToMono(byte[].class);

response.subscribe(result ->{System.out.println("请求成功");if(result !=null)System.out.println("result length is "+ result.length);}, throwable ->{
    throwable.printStackTrace();});

• 输出结果，不使用 DataBuffer，会因为数据量超过了设定的最大限制而报错

org.springframework.web.reactive.function.client.WebClientResponseException: 200 OK from GET http://127.0.0.1:9999/file/download/1.png
Caused by: org.springframework.core.io.buffer.DataBufferLimitException: Exceeded limit on max bytes to buffer : 262144

2、处理策略

• 调整数据量的最大限制

int size =10*1024*1024;ExchangeStrategies strategies =ExchangeStrategies.builder().codecs(codecs -> codecs.defaultCodecs().maxInMemorySize(size)).build();WebClient webClient =WebClient.builder().exchangeStrategies(strategies).build();Mono<byte[]> response = webClient.get().uri("http://127.0.0.1:9999/file/download/1.png").accept(MediaType.IMAGE_JPEG,MediaType.IMAGE_PNG).retrieve().bodyToMono(byte[].class);

response.subscribe(result ->{System.out.println("请求成功");if(result !=null)System.out.println("result length is "+ result.length);}, throwable ->{
    throwable.printStackTrace();});

三、泛型响应

1、问题案例

（1）Entity

• Person.java

@Data@NoArgsConstructor@AllArgsConstructorpublicclassPerson<T>{privateString name;privateint age;privateT thing;}

• Computer.java

@Data@NoArgsConstructor@AllArgsConstructorpublicclassComputer{privateString name;privateDouble price;}

（2）Server

@GetMapping("/testGeneric")publicPerson<Computer>testGeneric(){Computer computer =newComputer("联想电脑",8999.0);Person<Computer> person =newPerson<Computer>("张三",20, computer);return person;}

（3）Client

WebClient webClient =WebClient.create();Mono<Person> response = webClient.get().uri("http://127.0.0.1:9999/test/testGeneric").retrieve().bodyToMono(Person.class);

response.subscribe(person ->{System.out.println("请求成功");System.out.println(person);Computer computer =(Computer) person.getThing();System.out.println(computer);}, throwable ->{System.out.println("请求失败，结果为："+ throwable.getMessage());});

• 输出结果，对于嵌套的泛型强转失败

请求成功
Person(name=张三, age=20, thing={name=联想电脑, price=8999.0})
请求失败，结果为：class java.util.LinkedHashMap cannot be cast to class com.zy.api.Computer (java.util.LinkedHashMap is in module java.base of loader 'bootstrap'; com.zy.api.Computer is in unnamed module of loader 'app')

2、处理策略

• 正确指示 bodyToMono 方法

WebClient webClient =WebClient.create();Mono<Person<Computer>> response = webClient.get().uri("http://127.0.0.1:9999/test/testGeneric").retrieve().bodyToMono(newParameterizedTypeReference<Person<Computer>>(){});

response.subscribe(person ->{System.out.println("请求成功");System.out.println(person);Computer computer = person.getThing();System.out.println(computer);}, throwable ->{System.out.println("请求失败，结果为："+ throwable.getMessage());});

四、跟随重定向响应

1、问题案例

（1）Server

server:port:9999spring:mvc:static-path-pattern: /file/download/**web:resources:static-locations: file:D:/fileUpload/

@GetMapping("/testRedirect2Image")publicResponseEntitytestRedirect2Image(){returnResponseEntity.status(HttpStatus.SEE_OTHER).header("Location","http://127.0.0.1:9999/file/download/1.png").build();}

（2）Client

WebClient webClient =WebClient.create();

webClient.get().uri("http://127.0.0.1:9999/test/testRedirect2Image").accept(MediaType.IMAGE_JPEG,MediaType.IMAGE_PNG)// 指定了客户端期望接受的响应内容类型.retrieve()// 获取响应.bodyToFlux(DataBuffer.class)// 将响应体转换为 Flux<DataBuffer>.reduce(neworg.apache.tomcat.util.http.fileupload.ByteArrayOutputStream(),(baos, dataBuffer)->{try{byte[] bytes =newbyte[dataBuffer.readableByteCount()];
                dataBuffer.read(bytes);
                baos.write(bytes);DataBufferUtils.release(dataBuffer);}catch(IOException e){
                e.printStackTrace();DataBufferUtils.release(dataBuffer);returnnull;}return baos;}).map(byteArrayOutputStream ->{if(byteArrayOutputStream ==null)returnnull;return byteArrayOutputStream.toByteArray();}).subscribe(result ->{if(result ==null){System.out.println("result is null");return;}System.out.println("result length: "+ result.length);}, throwable ->{
            throwable.printStackTrace();});

• 输出结果，默认不会跟随重定向响应

result length: 0

2、处理策略

• 收到开启跟随重定向响应

HttpClient httpClient =HttpClient.create().followRedirect(true);// 允许跟随重定向WebClient webClient =WebClient.builder().clientConnector(newReactorClientHttpConnector(httpClient)).build();

webClient.get().uri("http://127.0.0.1:9999/test/testRedirect2Image").accept(MediaType.IMAGE_JPEG,MediaType.IMAGE_PNG)// 指定了客户端期望接受的响应内容类型.retrieve()// 获取响应.bodyToFlux(DataBuffer.class)// 将响应体转换为 Flux<DataBuffer>.reduce(neworg.apache.tomcat.util.http.fileupload.ByteArrayOutputStream(),(baos, dataBuffer)->{try{byte[] bytes =newbyte[dataBuffer.readableByteCount()];
                dataBuffer.read(bytes);
                baos.write(bytes);DataBufferUtils.release(dataBuffer);}catch(IOException e){
                e.printStackTrace();DataBufferUtils.release(dataBuffer);returnnull;}return baos;}).map(byteArrayOutputStream ->{if(byteArrayOutputStream ==null)returnnull;return byteArrayOutputStream.toByteArray();}).subscribe(result ->{if(result ==null){System.out.println("result is null");return;}System.out.println("result length: "+ result.length);}, throwable ->{
            throwable.printStackTrace();});

五、SSL 证书

1、问题案例

WebClient webClient =WebClient.create();Mono<byte[]> response = webClient.get().uri(url).accept(MediaType.IMAGE_JPEG,MediaType.IMAGE_PNG).retrieve().bodyToFlux(DataBuffer.class).reduce(newByteArrayOutputStream(),(baos, dataBuffer)->{try{byte[] bytes =newbyte[dataBuffer.readableByteCount()];
                dataBuffer.read(bytes);
                baos.write(bytes);DataBufferUtils.release(dataBuffer);}catch(IOException e){
                e.printStackTrace();DataBufferUtils.release(dataBuffer);returnnull;}return baos;}).map(byteArrayOutputStream ->{if(byteArrayOutputStream ==null)returnnull;return byteArrayOutputStream.toByteArray();});

response.subscribe(result ->{System.out.println("请求成功");if(result !=null)System.out.println("result length is "+ result.length);}, throwable ->{
    throwable.printStackTrace();});

• 输出结果

org.springframework.web.reactive.function.client.WebClientRequestException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target

2、忽略 SSL 证书

SslContext context =SslContextBuilder.forClient().trustManager(InsecureTrustManagerFactory.INSTANCE).build();HttpClient httpClient =HttpClient.create().secure(t -> t.sslContext(context));WebClient webClient =WebClient.builder().clientConnector(newReactorClientHttpConnector(httpClient)).build();Mono<byte[]> response = webClient.get().uri(url).accept(MediaType.IMAGE_JPEG,MediaType.IMAGE_PNG).retrieve().bodyToFlux(DataBuffer.class).reduce(newByteArrayOutputStream(),(baos, dataBuffer)->{try{byte[] bytes =newbyte[dataBuffer.readableByteCount()];
                dataBuffer.read(bytes);
                baos.write(bytes);DataBufferUtils.release(dataBuffer);}catch(IOException e){
                e.printStackTrace();DataBufferUtils.release(dataBuffer);returnnull;}return baos;}).map(byteArrayOutputStream ->{if(byteArrayOutputStream ==null)returnnull;return byteArrayOutputStream.toByteArray();});

response.subscribe(result ->{System.out.println("请求成功");if(result !=null)System.out.println("result length is "+ result.length);}, throwable ->{
    throwable.printStackTrace();});