如何在 Android 中使用 Volley 发出有效的 POST 多部分请求？

使用最新 API 通过 Volley 处理 POST 多部分请求

在 Android 开发中，发送多部分请求（例如上传文件和文本数据）是一项共同的任务。虽然 HttpEntity 在较新的 API 版本中不再可用，但仍然有一些方法可以使用 Volley 实现多部分请求。

创建基本多部分请求

创建多部分请求，我们可以像这样扩展 Volley 的 Request 类：

import com.android.volley.AuthFailureError;
import com.android.volley.NetworkResponse;
import com.android.volley.ParseError;
import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.HttpHeaderParser;

import java.util.Map;

class MultipartRequest extends Request<NetworkResponse> {
    // Listener for request response
    private final Response.Listener<NetworkResponse> mListener;
    // Listener for request error
    private final Response.ErrorListener mErrorListener;
    // Request headers
    private final Map<String, String> mHeaders;
    // Multipart mime type (e.g., "multipart/form-data; boundary=XXX")
    private final String mMimeType;
    // Request body as multipart
    private final byte[] mMultipartBody;

    // Constructor
    public MultipartRequest(String url, Map<String, String> headers, String mimeType, byte[] multipartBody,
                            Response.Listener<NetworkResponse> listener, Response.ErrorListener errorListener) {
        super(Method.POST, url, errorListener);
        this.mListener = listener;
        this.mErrorListener = errorListener;
        this.mHeaders = headers;
        this.mMimeType = mimeType;
        this.mMultipartBody = multipartBody;
    }

    // Getters and setters

    // Override getHeaders() if you need to add custom headers
    @Override
    public Map<String, String> getHeaders() throws AuthFailureError {
        return (mHeaders != null) ? mHeaders : super.getHeaders();
    }

    // Override getBodyContentType() to set the correct mime type for the multipart request
    @Override
    public String getBodyContentType() {
        return mMimeType;
    }

    // Override getBody() to return the multipart body
    @Override
    public byte[] getBody() throws AuthFailureError {
        return mMultipartBody;
    }

    // Override parseNetworkResponse() to parse the response as a NetworkResponse
    @Override
    protected Response<NetworkResponse> parseNetworkResponse(NetworkResponse response) {
        try {
            return Response.success(
                    response,
                    HttpHeaderParser.parseCacheHeaders(response));
        } catch (Exception e) {
            return Response.error(new ParseError(e));
        }
    }

    // Delivering response and error
    @Override
    protected void deliverResponse(NetworkResponse response) {
        mListener.onResponse(response);
    }

    @Override
    public void deliverError(VolleyError error) {
        mErrorListener.onErrorResponse(error);
    }
}

构建多部分主体

要构建多部分主体，我们可以使用以下步骤：

byte[] multipartBody = new byte[0];
ByteArrayOutputStream bos = new ByteArrayOutputStream();
DataOutputStream dos = new DataOutputStream(bos);
try {
    // Text data
    buildTextPart(dos, "name", "John Doe");
    buildTextPart(dos, "email", "john.doe@email.com");

    // Image data
    Bitmap imageBitmap = BitmapFactory.decodeResource(context.getResources(), R.drawable.my_image);
    buildImagePart(dos, "image", imageBitmap);

} catch (IOException e) {
    e.printStackTrace();
}
multipartBody = bos.toByteArray();

在请求中包含多部分主体

一旦构建了多部分主体，我们就可以将其包含在我们的 MultipartRequest 实例中，例如so:

MultipartRequest request = new MultipartRequest(
        "my_url",
        null, // Headers
        "multipart/form-data",
        multipartBody,
        new Response.Listener<NetworkResponse>() {
            @Override
            public void onResponse(NetworkResponse response) {
                // Handle response
            }
        },
        new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                // Handle error
            }
        });

在请求中添加文本数据

除了图像数据，您还可以在请求中包含文本数据：

private void buildTextPart(DataOutputStream dataOutputStream, String name, String value) throws IOException {
    dataOutputStream.writeBytes(twoHyphens + boundary + lineEnd);
    dataOutputStream.writeBytes("Content-Disposition: form-data; name=\"" + name + "\"" + lineEnd);
    dataOutputStream.writeBytes(lineEnd);
    dataOutputStream.writeBytes(value);
    dataOutputStream.writeBytes(lineEnd);
}

将两个连字符、边界和 lineEnd 替换为您的适当值code.

完整代码示例

以下代码示例显示了 VolleyMultipartRequest 类的完整模块化实现：

import com.android.volley.AuthFailureError;
import com.android.volley.NetworkResponse;
import com.android.volley.ParseError;
import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.HttpHeaderParser;

import java.io.ByteArrayOutputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

public class VolleyMultipartRequest extends Request<NetworkResponse> {
    private final Response.Listener<NetworkResponse> mListener;
    private final Response.ErrorListener mErrorListener;
    private final Map<String, String> mHeaders;
    private final String mMimeType;
    private final byte[] mMultipartBody;

    public VolleyMultipartRequest(int method, String url, Response.Listener<NetworkResponse> listener,
                                  Response.ErrorListener errorListener) {
        super(method, url, errorListener);
        this.mListener = listener;
        this.mErrorListener = errorListener;
        this.mHeaders = null;
        this.mMimeType = null;
        this.mMultipartBody = null;
    }

    public VolleyMultipartRequest(String url, Map<String, String> headers, String mimeType, byte[] multipartBody,
                                  Response.Listener<NetworkResponse> listener, Response.ErrorListener errorListener) {
        super(Method.POST, url, errorListener);
        this.mListener = listener;
        this.mErrorListener = errorListener;
        this.mHeaders = headers;
        this.mMimeType = mimeType;
        this.mMultipartBody = multipartBody;
    }

    @Override
    public Map<String, String> getHeaders() throws AuthFailureError {
        return (mHeaders != null) ? mHeaders : super.getHeaders();
    }

    @Override
    public String getBodyContentType() {
        return mMimeType;
    }

    @Override
    public byte[] getBody() throws AuthFailureError {
        return mMultipartBody;
    }

    @Override
    protected Response<NetworkResponse> parseNetworkResponse(NetworkResponse response) {
        try {
            return Response.success(
                    response,
                    HttpHeaderParser.parseCacheHeaders(response));
        } catch (Exception e) {
            return Response.error(new ParseError(e));
        }
    }

    @Override
    protected void deliverResponse(NetworkResponse response) {
        mListener.onResponse(response);
    }

    @Override
    public void deliverError(VolleyError error) {
        mErrorListener.onErrorResponse(error);
    }

    public static Map<String, DataPart> createMultipartRequestParts(Map<String, String> params, Map<String, DataPart> data) {
        Map<String, DataPart> multipartParams = new HashMap<>();
        for (Map.Entry<String, String> entry : params.entrySet()) {
            multipartParams.put(entry.getKey(), new DataPart(entry.getValue()));
        }
        for (Map.Entry<String, DataPart> entry : data.entrySet()) {
            multipartParams.put(entry.getKey(), entry.getValue());
        }
        return multipartParams;
    }

    public static byte[] createMultipartBody(Map<String, DataPart> data, String boundary) throws IOException {
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        DataOutputStream dos = new DataOutputStream(bos);
        for (Map.Entry<String, DataPart> entry : data.entrySet()) {
            buildTextPart(dos, entry.getKey(), entry.getValue().getContentType(), entry.getValue().getFileName(), entry.getValue().getData());
        }

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