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();
});