Callback请求中函数最后一个参数是一个Callback的实例，httpExecutor是一个Executor，用于执行Runnable请求，我们看到，这里new了一个CallbackRunnable执行，并实现了它的obtainResponse方法，看实现：
abstract class CallbackRunnable<T> implements Runnable {
private final Callback<T> callback;
private final Executor callbackExecutor;
private final ErrorHandler errorHandler;
CallbackRunnable(Callback<T> callback, Executor callbackExecutor, ErrorHandler errorHandler) {
this.callback = callback;
this.callbackExecutor = callbackExecutor;
this.errorHandler = errorHandler;
}
@SuppressWarnings("unchecked")
@Override public final void run() {
try {
final ResponseWrapper wrapper = obtainResponse();
callbackExecutor.execute(new Runnable() {
@Override public void run() {
callback.success((T) wrapper.responseBody, wrapper.response);
}
});
} catch (RetrofitError e) {
Throwable cause = errorHandler.handleError(e);
final RetrofitError handled = cause == e ? e : unexpectedError(e.getUrl(), cause);
callbackExecutor.execute(new Runnable() {
@Override public void run() {
callback.failure(handled);
}
});
}
}
public abstract ResponseWrapper obtainResponse();
}
就是一个普通的Runnable，在run方法中首先执行obtailResponse，从名字可以看到是执行请求返回Response，这个从前面可以看到执行了invokeRequest，和同步调用中一样执行请求。
紧接着就提交了一个Runnable至callbackExecutor，在看Platform时看到了callbackExecotor是通过Platform.get().defaultCallbackExecutor()返回的，Android中是向主线程的一个Handler发消息
值得注意的事，对于同步调用，如果遇到错误是直接抛异常，而对于异步调用，是调用Callback.failure()
Mime
执行网络请求，需要向服务端发送请求参数，如表单数据，上传的文件等，同样需要解析服务端返回的数据，在Retrofit中对这些做了封装，位于Mime包中，也只有封装了，才好统一由指定的Converter执行数据的转换
TypedInput和TypedOutput表示输入输出的数据，都包含mimeType，并分别支持读入一个InputStream或写到一个OutputStrem
/**
* Binary data with an associated mime type.
*
* @author Jake Wharton (jw@squareup.com)
*/
public interface TypedInput {
/** Returns the mime type. */
String mimeType();
/** Length in bytes. Returns {@code -1} if length is unknown. */
long length();
/**
* Read bytes as stream. Unless otherwise specified, this method may only be called once. It is
* the responsibility of the caller to close the stream.
*/
InputStream in() throws IOException;
}
/**
* Binary data with an associated mime type.
*
* @author Bob Lee (bob@squareup.com)
*/
public interface TypedOutput {
/** Original filename.
*
* Used only for multipart requests, may be null. */
String fileName();
/** Returns the mime type. */
String mimeType();
/** Length in bytes or -1 if unknown. */
long length();
/** Writes these bytes to the given output stream. */
void writeTo(OutputStream out) throws IOException;
}
TypedByteArray，内部数据是一个Byte数组
private final byte[] bytes;
@Override public long length() {
return bytes.length;
}
@Override public void writeTo(OutputStream out) throws IOException {
out.write(bytes);
}
@Override public InputStream in() throws IOException {
return new ByteArrayInputStream(bytes);
}
TypedString，继承自TypedByteArray，内部表示是一样的
public TypedString(String string) {
super("text/plain; charset=UTF-8", convertToBytes(string));
}
private static byte[] convertToBytes(String string) {
try {
return string.getBytes("UTF-8");
} catch (UnsupportedEncodingException e) {
throw new RuntimeException(e);
}
}
