okhttp攔截器作為它的重要一員，如果好好利用往往能使我們事半功倍，先看一下攔截器的核心介面Interceptor：

public interface Interceptor {
  Response intercept(Chain chain) throws IOException;

  interface Chain {
    Request request();

    Response proceed(Request request) throws IOException;

    Connection connection();
  }
}

要實現攔截，就要定義類實現介面Interceptor

下面簡單總結一下intercept 方法中可以實現的功能：

實現介面

在開始之前，我們先定義LoggingInterceptor實現介面Interceptor，其中的變數和方法後面會用到：

public final class LoggingInterceptor implements Interceptor {

    private static final Charset UTF8 = Charset.forName("UTF-8");
    public static
 
 final String HTTP_HEADER = "<string xmlns=\"http://schemas.microsoft.com/2003/10/Serialization/\">";
    public static final String HTTP_TAIL = "</string>";

    private boolean isPlaintext(Buffer buffer) {
        try {
            Buffer prefix = new Buffer();
            long byteCount = buffer.size() < 64
 
 ? buffer.size() : 64;
            buffer.copyTo(prefix, 0, byteCount);
            for (int i = 0; i < 16; i++) {
                if (prefix.exhausted()) {
                    break;
                }
                int codePoint = prefix.readUtf8CodePoint();
                if (Character.isISOControl(codePoint) && !Character.isWhitespace(codePoint)) {
                    return false;
                }
            }
            return true;
        } catch (EOFException e) {
            return false; // Truncated UTF-8 sequence.
        }
    }

    private boolean bodyEncoded(Headers headers) {
        String contentEncoding = headers.get("Content-Encoding");
        return contentEncoding != null && !contentEncoding.equalsIgnoreCase("identity");
    }

    private String protocol(Protocol protocol) {
        return protocol == Protocol.HTTP_1_0 ? "HTTP/1.0" : "HTTP/1.1";
    }
}

列印請求

    @Override
    public Response intercept(Chain chain) throws IOException {
        Request request = chain.request();
        RequestBody requestBody = request.body();
        boolean hasRequestBody = requestBody != null;
        Connection connection = chain.connection();
        Protocol protocol = connection != null ? connection.protocol() : Protocol.HTTP_1_1;
        String requestStartMessage =
                "--> " + request.method() + ' ' + request.url() + ' ' + protocol(protocol);
        //請求方法及url等
        logger.log(requestStartMessage);

        logger.log("---請求頭---");
        Headers headers = request.headers();
        for (int i = 0, count = headers.size(); i < count; i++) {
            logger.log(headers.name(i) + ": " + headers.value(i));
        }

        logger.log("---請求引數---");
        HttpUrl url = request.url();
        for (String name : url.queryParameterNames()) {
            StringBuffer sb = new StringBuffer();
            sb.append(url.queryParameterValues(name));
            //去除頭尾多餘的"[]"
            sb.deleteCharAt(sb.length() - 1);
            sb.deleteCharAt(0);
            logger.log(name + ": " + sb);
        }

        logger.log("---請求體---");
        if (hasRequestBody && !bodyEncoded(headers)) {
            Buffer buffer = new Buffer();
            requestBody.writeTo(buffer);
            Charset charset = UTF8;
            MediaType contentType = requestBody.contentType();
            if (contentType != null) {
                charset = contentType.charset(UTF8);
            }
            if (isPlaintext(buffer)) {
                logger.log(buffer.readString(charset).replaceAll("&", "\n"));
            }
        }
        //請求結束
        logger.log("");
        logger.log("--> END Request");
        logger.log("");

        return chain.proceed(request);
    }

修改請求

修改請求頭

    @Override
    public Response intercept(Chain chain) throws IOException {
        Request original = chain.request();
        Request.Builder requestBuilder = original.newBuilder()
                .method(original.method(), original.body());
        Headers.Builder header = new Headers.Builder();
        header.add("os", "android");
        header.add("version", "1.2.5");
        Request request = requestBuilder.headers(header.build()).build();
        return chain.proceed(request);
    }

修改請求體

這種修改只針對以下的需求：

• 得到原始的請求體字串，如{"name":"Sbingo","job":"android developer"}
• 在字串中新增secret Key/Value對，得到{"name":"Sbingo","job":"android developer","secret":"F910EUY09"}
• 在字串前後新增標籤

<string xmlns="http://schemas.microsoft.com/2003/10/Serialization/">{"name":"Sbingo","job":"android developer","secret":"F910EUY09"}</string>

• 使用上一步得到的字串作為請求體

    @Override
    public Response intercept(Chain chain) throws IOException {
        Request originalRequest = chain.request();
        Request newRequest;
        if (originalRequest.body() instanceof FormBody) {
            Request.Builder requestBuilder = originalRequest.newBuilder();
            StringBuilder jsonRequest = new StringBuilder();
            jsonRequest.append("{");
            FormBody oldFormBody = (FormBody) originalRequest.body();
            for (int i = 0; i < oldFormBody.size(); i++) {
                String name = oldFormBody.encodedName(i);
                String value = oldFormBody.encodedValue(i);
                jsonRequest.append("\"");
                jsonRequest.append(name);
                jsonRequest.append("\":\"");
                jsonRequest.append(value);
                jsonRequest.append("\"");
                jsonRequest.append(",");
            }
            jsonRequest.append("\"secret\":\"");
            jsonRequest.append("F910EUY09");
            jsonRequest.append("\"");
            jsonRequest.append("}");
            String request = HTTP_HEADER + jsonRequest.toString() + HTTP_TAIL;
            MediaType mediaType = MediaType.parse("text/xml; charset=utf-8");
            newRequest = requestBuilder.post(RequestBody.create(mediaType, request)).build();
        } else {
            throw new RuntimeException("請使用表單提交網路請求！");
        }
        return chain.proceed(newRequest);
    }

列印響應

    @Override
    public Response intercept(Chain chain) throws IOException {
        Request request = chain.request();
        long startNs = System.nanoTime();
        Response response = chain.proceed(request);
        long tookMs = TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startNs);

        ResponseBody responseBody = response.body();
        //響應碼及url等
        logger.log("<-- "
                + response.code()
                + ' '
                + response.message()
                + ' '
                + response.request().url()
                + " ("
                + tookMs
                + "ms"
                + ')');

        logger.log("---響應頭---");
        Headers responseHeaders = response.headers();
        for (int i = 0, count = responseHeaders.size(); i < count; i++) {
            logger.log(responseHeaders.name(i) + ": " + responseHeaders.value(i));
        }

        logger.log("---響應體---");
        if (HttpHeaders.hasBody(response) && !bodyEncoded(responseHeaders)) {
            BufferedSource source = responseBody.source();
            source.request(Long.MAX_VALUE);
            Buffer responseBuffer = source.buffer();
            Charset responseCharset = UTF8;
            MediaType responseContentType = responseBody.contentType();
            if (responseContentType != null) {
                responseCharset = responseContentType.charset(UTF8);
            }
            if (isPlaintext(responseBuffer)) {
                com.orhanobut.logger.Logger.json(responseBuffer.clone().readString(responseCharset));
            }
        }
        logger.log("");
        logger.log("<-- END Response");

        return response;
    }