[享学Feign] 十、Feign通过feign-jackson模块天然支持POJO的编码和解码

/**
 * 查询列表
 */
@RequestLine("GET /person/list")
List<Person> getList();

/**
 * 新增一条记录
 */
@RequestLine("POST /person")
Long create(Person person);

<dependency>
    <groupId>io.github.openfeign</groupId>
    <artifactId>feign-jackson</artifactId>
    <version>${feign.version}</version>
</dependency>

@Getter
@Setter
public class Person {
    private String name = "YourBatman";
    private Integer age = 18;
}

public interface JacksonDemoClient {

    @RequestLine("POST /feign/jacksondemo")
    String jacksonDemo1(String body);

    @RequestLine("POST /feign/jacksondemo")
    String jacksonDemo2(Person person);
}

@Test
public void fun2() {
    JacksonDemoClient client = Feign.builder()
            .logger(new Logger.ErrorLogger()).logLevel(Logger.Level.FULL).retryer(Retryer.NEVER_RETRY) // 输出日志
            .target(JacksonDemoClient.class, "http://localhost:8080");

    try { client.jacksonDemo1("this is http body"); }catch (Exception e) { e.printStackTrace();}

    System.err.println(" -------------------------- ");

    try { client.jacksonDemo2(new Person()); }catch (Exception e) { e.printStackTrace();}
}

// 第一个请求完全正常，因为是String类型
[JacksonDemoClient#jacksonDemo1] ---> POST http://localhost:8080/feign/jacksondemo HTTP/1.1
[JacksonDemoClient#jacksonDemo1] Content-Length: 17
[JacksonDemoClient#jacksonDemo1] 
[JacksonDemoClient#jacksonDemo1] this is http body
[JacksonDemoClient#jacksonDemo1] ---> END HTTP (17-byte body)
...
 -------------------------- 
 
// 第二个抛错：Person不能被编码
feign.codec.EncodeException: class com.yourbatman.modules.beans.Person is not a type supported by this encoder.
	at feign.codec.Encoder$Default.encode(Encoder.java:94)
	...

@Test
public void fun3() throws JsonProcessingException {
    JacksonDemoClient client = Feign.builder()
            .logger(new Logger.ErrorLogger()).logLevel(Logger.Level.FULL).retryer(Retryer.NEVER_RETRY) // 输出日志
            .target(JacksonDemoClient.class, "http://localhost:8080");

    // 手动完成编码操作，编码为字符串
    ObjectMapper mapper = new ObjectMapper();
    String bodyStr =  mapper.writeValueAsString(new Person());

    // 然后调用方法一完成请求发送
    try { client.jacksonDemo1(bodyStr); }catch (Exception e) { e.printStackTrace();}
}

[JacksonDemoClient#jacksonDemo1] ---> POST http://localhost:8080/feign/jacksondemo HTTP/1.1
[JacksonDemoClient#jacksonDemo1] Content-Length: 30
[JacksonDemoClient#jacksonDemo1] 
[JacksonDemoClient#jacksonDemo1] {"name":"YourBatman","age":18}
[JacksonDemoClient#jacksonDemo1] ---> END HTTP (30-byte body)
...

// 编码器显示指定使用`JacksonEncoder`
@Test
public void fun3() {
    JacksonDemoClient client = Feign.builder()
    		.logger(new Logger.ErrorLogger()).logLevel(Logger.Level.FULL).retryer(Retryer.NEVER_RETRY) // 输出日志
            .encoder(new JacksonEncoder())
            .target(JacksonDemoClient.class, "http://localhost:8080");

    client.jacksonDemo2(new Person());
}

[JacksonDemoClient#jacksonDemo2] ---> POST http://localhost:8080/feign/jacksondemo HTTP/1.1
[JacksonDemoClient#jacksonDemo2] Content-Length: 44
[JacksonDemoClient#jacksonDemo2] 
[JacksonDemoClient#jacksonDemo2] {
  "name" : "YourBatman",
  "age" : 18
}
[JacksonDemoClient#jacksonDemo2] ---> END HTTP (44-byte body)
...

...
client.jacksonDemo2(null);
...

public class JacksonEncoder implements Encoder {

	private final ObjectMapper mapper;

	// 构造器
	public JacksonEncoder() {
	    this(Collections.emptyList());
	}
 // 你可为ObjectMapper注册任意的模块
  public JacksonEncoder(Iterable<Module> modules) {
    this(new ObjectMapper()
    	// 值为null的key是不会序列化到JSON串的
    	// 而ObjectMapper的默认行为是会序列化进去的哦
        .setSerializationInclusion(JsonInclude.Include.NON_NULL)
        // 默认会美化输出
        // 其实我觉得生产上次属性可置为false，没啥必要
        .configure(SerializationFeature.INDENT_OUTPUT, true)
        // 注册module模块们
        .registerModules(modules));
  }

	// 若默认的ObjectMapper不如你意，你可以用你自己的
	// 比如SpringBoot容器内的ObjectMapper作为全局使用的~~~~比较好
  public JacksonEncoder(ObjectMapper mapper) {
    this.mapper = mapper;
  }

	// 执行编码
  @Override
  public void encode(Object object, Type bodyType, RequestTemplate template) {
    ...
    // 采用UTF-8编码，把字符串/POJO写为Byte数组放进Body体里
    template.body(mapper.writerFor(javaType).writeValueAsBytes(object), Util.UTF_8);
    ...
  }
}

public class JacksonDecoder implements Decoder {

	private final ObjectMapper mapper;

	... // 构造器。会帮你关闭`DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES`这个特征
	...

  @Override
  public Object decode(Response response, Type type) throws IOException {
	// 如果木有body，就返回null呗
    if (response.body() == null)
      return null;
	... 
	return mapper.readValue(reader, mapper.constructType(type));
  }

}

public interface DecoderClient {

    @RequestLine("GET /feign/demo1/list")
    List<String> getDemo1List();
}

@Test
public void fun4() {
    DecoderClient client = Feign.builder()
    		.decoder(new JacksonDecoder()) // 使用Jackson解码
            .target(DecoderClient.class, "http://localhost:8080");

    List<String> list = client.getDemo1List();
    System.out.println(list);
}

@RequestLine("GET /feign/demo1/list")
Stream<String> getDemo1List();

feign.FeignException: Cannot construct instance of `java.util.stream.Stream` (no Creators, like default construct, exist): abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information
 at [Source: (BufferedReader); line: 1, column: 1] reading GET http://localhost:8080/feign/demo1/list
 ...

@RequestLine("GET /feign/demo1/list")
Iterator<String> getDemo1List2();


@Test
public void fun5() {
    DecoderClient client = Feign.builder()
            .decoder(JacksonIteratorDecoder.create())
            .target(DecoderClient.class, "http://localhost:8080");

    Iterator<String> it = client.getDemo1List2();
    while(it.hasNext()){
        System.out.println(it.next());
    }
}

A
B
C

Feign.builder().decoder(StreamDecoder.create(JacksonIteratorDecoder.create()))