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”)
public String testBigData() {
int targetSize = 1024 * 1024; // 1MB
StringBuilder sb = new StringBuilder(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 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: 9999
spring:
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
@AllArgsConstructor
public class Person {
private String name;
private int age;
private T thing;
}
Computer.java

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Computer {
private String name;
private Double price;
}

（2）Server

@GetMapping("/testGeneric")
public Person<Computer> testGeneric() {Computer computer = new Computer("联想电脑", 8999.0);Person<Computer> person = new Person<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> response = webClient.get()
.uri(“http://127.0.0.1:9999/test/testGeneric”)
.retrieve()
.bodyToMono(new ParameterizedTypeReference<Person>() {
});

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: 9999
spring:mvc:static-path-pattern: /file/download/**web:resources:static-locations: file:D:/fileUpload/@GetMapping("/testRedirect2Image")
public ResponseEntity testRedirect2Image() {return ResponseEntity.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(new org.apache.tomcat.util.http.fileupload.ByteArrayOutputStream(), (baos, dataBuffer) -> {try {byte[] bytes = new byte[dataBuffer.readableByteCount()];dataBuffer.read(bytes);baos.write(bytes);DataBufferUtils.release(dataBuffer);} catch (IOException e) {e.printStackTrace();DataBufferUtils.release(dataBuffer);return null;}return baos;}).map(byteArrayOutputStream -> {if (byteArrayOutputStream == null) return null;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(new ReactorClientHttpConnector(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
.reduce(new org.apache.tomcat.util.http.fileupload.ByteArrayOutputStream(), (baos, dataBuffer) -> {
try {
byte[] bytes = new byte[dataBuffer.readableByteCount()];
dataBuffer.read(bytes);
baos.write(bytes);
DataBufferUtils.release(dataBuffer);
} catch (IOException e) {
e.printStackTrace();
DataBufferUtils.release(dataBuffer);
return null;
}
return baos;
})
.map(byteArrayOutputStream -> {
if (byteArrayOutputStream == null) return null;
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(new ByteArrayOutputStream(), (baos, dataBuffer) -> {try {byte[] bytes = new byte[dataBuffer.readableByteCount()];dataBuffer.read(bytes);baos.write(bytes);DataBufferUtils.release(dataBuffer);} catch (IOException e) {e.printStackTrace();DataBufferUtils.release(dataBuffer);return null;}return baos;}).map(byteArrayOutputStream -> {if (byteArrayOutputStream == null) return null;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(new ReactorClientHttpConnector(httpClient)).build();Mono<byte[]> response = webClient.get().uri(url).accept(MediaType.IMAGE_JPEG, MediaType.IMAGE_PNG).retrieve().bodyToFlux(DataBuffer.class).reduce(new ByteArrayOutputStream(), (baos, dataBuffer) -> {try {byte[] bytes = new byte[dataBuffer.readableByteCount()];dataBuffer.read(bytes);baos.write(bytes);DataBufferUtils.release(dataBuffer);} catch (IOException e) {e.printStackTrace();DataBufferUtils.release(dataBuffer);return null;}return baos;}).map(byteArrayOutputStream -> {if (byteArrayOutputStream == null) return null;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();
});