android volley multipart

最近主要从事android app方向开发工作，在项目里遇到了一个关于图片上传使用multipart的问题，所以拿出来说说。

项目的服务端用php写的，服务端童鞋在写关于图片上传api的时候直接用了 $_FILE，因此需要客户端实现multipart请求来完成图片上传。在android-async-http库里，只要params.add(“foo”, file) 就传入File对象，然后直接发送请求，底层就会帮你实现multipart。而在我刚接手这个项目的时候我选择了volley，其原因是因为android-async-http底层使用apache的HttpClient库，而这个库在6.0版本中已经被移除了（不是废弃）。

volley库在正常情况下其实是很好用的，但我没有找到关于multipart的支持，所以只好自己写一个简单拼接multipart的writer。

package org.vizee.mime;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.LinkedList;
import java.util.Random;

/**
 * Simple multipart body writer
 * Created by vizee on 15-10-10.
 */
public class MultipartWriter {

    private static final byte[] APPLICATION_OCTET_STREAM = "application/octet-stream".getBytes();
    private static final byte[] CONTENT_TYPE = "Content-Type: ".getBytes();
    private static final byte[] CONTENT_DISPOSITION_FORM_DATA = "Content-Disposition: form-data; ".getBytes();
    private static final byte[] CONTENT_DISPOSITION_NAME = "name=\"".getBytes();
    private static final byte[] CONTENT_DISPOSITION_FILENAME = "filename=\"".getBytes();
    private static final byte[] CONTENT_DISPOSITION_SPLIT = "\"; ".getBytes();
    private static final byte[] CONTENT_DISPOSITION_END = "\"\r\n".getBytes();
    private static final byte[] CRLF = "\r\n".getBytes();
    private static final byte[] TRANSFER_ENCODING_BINARY = ("Content-Transfer-Encoding: binary\r\n").getBytes();

    private static final char[] MULTIPART_CHARS = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz".toCharArray();

    private String boundary;
    private LinkedList<byte[]> parts;

    public MultipartWriter() {
        this(randomBoundary(30));
    }

    public MultipartWriter(String boundary) {
        this.boundary = boundary;
        parts = new LinkedList<>();
    }

    public String getBoundary() {
        return boundary;
    }

    public void add(String key, String value) throws IOException {
        add(key, value, "text/plain; charset=UTF-8");
    }

    public void add(String key, String value, String type) throws IOException {
        // magic capacity
        ByteArrayOutputStream part = new ByteArrayOutputStream(100);
        addContentDisposition(part, key);
        addContentType(part, type);
        part.write(CRLF);
        part.write(value.getBytes());
        part.write(CRLF);
        parts.add(part.toByteArray());
    }

    public void add(String key, File file) throws IOException {
        FileInputStream inputStream = new FileInputStream(file);
        try {
            add(key, file.getName(), inputStream, null);
        } finally {
            try {
                inputStream.close();
            } catch (IOException ignored) {
            }
        }
    }

    public void add(String key, String filename, InputStream inputStream, String type) throws IOException {
        ByteArrayOutputStream part = new ByteArrayOutputStream(180);
        addContentDisposition(part, key, filename);
        addContentType(part, type);
        part.write(TRANSFER_ENCODING_BINARY);
        part.write(CRLF);
        final byte[] buf = new byte[4096];
        int n;
        while ((n = inputStream.read(buf)) != -1) {
            part.write(buf, 0, n);
        }
        part.write(CRLF);
        parts.add(part.toByteArray());
    }

    public byte[] getBytes() {
        byte[] boundaryDelim = ("--" + boundary + "\r\n").getBytes();
        byte[] boundaryEnd = ("--" + boundary + "--\r\n").getBytes();
        int total = parts.size() * boundaryDelim.length + boundaryEnd.length;
        for (byte[] part : parts) {
            total += part.length;
        }
        byte[] bytes = new byte[total];
        int p = 0;
        for (byte[] part : parts) {
            System.arraycopy(boundaryDelim, 0, bytes, p, boundaryDelim.length);
            p += boundaryDelim.length;
            System.arraycopy(part, 0, bytes, p, part.length);
            p += part.length;
        }
        System.arraycopy(boundaryEnd, 0, bytes, p, boundaryEnd.length);
        return bytes;
    }

    private static String randomBoundary(int length) {
        char[] chars = new char[length];
        Random rand = new Random();
        for (int i = 0; i < length; i++) {
            chars[i] = MULTIPART_CHARS[rand.nextInt(MULTIPART_CHARS.length)];
        }
        return String.valueOf(chars);
    }

    private static void addContentType(ByteArrayOutputStream header, String type) throws IOException {
        header.write(CONTENT_TYPE);
        if (type == null) {
            header.write(APPLICATION_OCTET_STREAM);
        } else {
            header.write(type.getBytes());
        }
        header.write(CRLF);
    }

    private static void addContentDisposition(ByteArrayOutputStream header, String name) throws IOException {
        addContentDisposition(header, name, null);
    }

    private static void addContentDisposition(ByteArrayOutputStream header, String name, String filename) throws IOException {
        header.write(CONTENT_DISPOSITION_FORM_DATA);
        header.write(CONTENT_DISPOSITION_NAME);
        header.write(name.getBytes());
        if (filename != null) {
            header.write(CONTENT_DISPOSITION_SPLIT);
            header.write(CONTENT_DISPOSITION_FILENAME);
            header.write(filename.getBytes());
        }
        header.write(CONTENT_DISPOSITION_END);
    }
}

然后需要重载volley.Request

package org.vizee.mime;

import com.android.volley.Request;
import com.android.volley.Response;

/**
 * Volley multipart request
 * Created by vizee on 15-10-10.
 */
public abstract class MultipartRequest<T> extends Request<T> {

    private byte[] body;
    private String contentType;

    public MultipartRequest(int method, String url, MultipartWriter writer, Response.ErrorListener listener) {
        super(method, url, listener);
        body = writer.getBytes();
        contentType = "multipart/form-data; boundary=" + writer.getBoundary();
    }

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

    @Override
    public byte[] getBody() {
        return body;
    }
}

至于volley怎么用就不用说了吧～