Fegin 第7 章：RequestTemplate

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李延 LV6 2021-06-22

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# 作用
RequestTemplate：request模版，可以将请求参数绑定至request中。首先在Contract中为每个fegin方法生成一个RequestTemplate对象，在请求调用时，通过RequestTemplate.Factory生成各种请求的RequestTemplate对象，并获取request。

# RequestTemplate.Factory
 为每个请求生成各自的RequestTemplate。

# 创建
在ParseHandlersByName类中我们看到它的创建过程

```java
    public Map<String, MethodHandler> apply(Target target) {
      List<MethodMetadata> metadata = contract.parseAndValidateMetadata(target.type());
      Map<String, MethodHandler> result = new LinkedHashMap<String, MethodHandler>();
      for (MethodMetadata md : metadata) {
        BuildTemplateByResolvingArgs buildTemplate;
        if (!md.formParams().isEmpty() && md.template().bodyTemplate() == null) {
          buildTemplate =
              new BuildFormEncodedTemplateFromArgs(md, encoder, queryMapEncoder, target);
        } else if (md.bodyIndex() != null) {
          buildTemplate = new BuildEncodedTemplateFromArgs(md, encoder, queryMapEncoder, target);
        } else {
          buildTemplate = new BuildTemplateByResolvingArgs(md, queryMapEncoder, target);
        }
        if (md.isIgnored()) {
          result.put(md.configKey(), args -> {
            throw new IllegalStateException(md.configKey() + " is not a method handled by feign");
          });
        } else {
          result.put(md.configKey(),
              factory.create(target, md, buildTemplate, options, decoder, errorDecoder));
        }
      }
      return result;
    }

```

我们看到根据不同的3种情况创建了3种不同的RequestTemplate.Factory

1. 只包含formParams参数时 使用BuildFormEncodedTemplateFromArgs对象
2. 包含body参数时 使用 BuildTemplateByResolvingArgs对象
3. 其他情况使用 BuildTemplateByResolvingArgs对象

## BuildTemplateByResolvingArgs

所有BuildTemplateByResolvingArgs都继承自它。我们主要看一下它create方法

```java
  @Override
    public RequestTemplate create(Object[] argv) {
      RequestTemplate mutable = RequestTemplate.from(metadata.template());
      mutable.feignTarget(target);
      if (metadata.urlIndex() != null) {
        int urlIndex = metadata.urlIndex();
        checkArgument(argv[urlIndex] != null, "URI parameter %s was null", urlIndex);
        mutable.target(String.valueOf(argv[urlIndex]));
      }
      Map<String, Object> varBuilder = new LinkedHashMap<String, Object>();
      for (Entry<Integer, Collection<String>> entry : metadata.indexToName().entrySet()) {
        int i = entry.getKey();
        Object value = argv[entry.getKey()];
        if (value != null) { // Null values are skipped.
          if (indexToExpander.containsKey(i)) {
            value = expandElements(indexToExpander.get(i), value);
          }
          for (String name : entry.getValue()) {
            varBuilder.put(name, value);
          }
        }
      }

RequestTemplate template = resolve(argv, mutable, varBuilder);
      if (metadata.queryMapIndex() != null) {
        // add query map parameters after initial resolve so that they take
        // precedence over any predefined values
        Object value = argv[metadata.queryMapIndex()];
        Map<String, Object> queryMap = toQueryMap(value);
        template = addQueryMapQueryParameters(queryMap, template);
      }

if (metadata.headerMapIndex() != null) {
        template =
            addHeaderMapHeaders((Map<String, Object>) argv[metadata.headerMapIndex()], template);
      }

return template;
    }

```

这里我们看到首先是从模版中复制一份RequestTemplate，并根据参数设置query、header等

# BuildFormEncodedTemplateFromArgs

```java

@Override
    protected RequestTemplate resolve(Object[] argv,
                                      RequestTemplate mutable,
                                      Map<String, Object> variables) {
      Map<String, Object> formVariables = new LinkedHashMap<String, Object>();
      for (Entry<String, Object> entry : variables.entrySet()) {
        if (metadata.formParams().contains(entry.getKey())) {
          formVariables.put(entry.getKey(), entry.getValue());
        }
      }
      try {
        encoder.encode(formVariables, Encoder.MAP_STRING_WILDCARD, mutable);
      } catch (EncodeException e) {
        throw e;
      } catch (RuntimeException e) {
        throw new EncodeException(e.getMessage(), e);
      }
      return super.resolve(argv, mutable, variables);
    }
  }
```

这里我们看到在之前的基础上添加了一个encoder处理body的过程

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