[Android] 解决Volley中JsonObjectReq

由于一开始官方介绍 Volley 适合轻量高并发的网络请求场景, 并不推荐用于上传下载, 因此以前只是粗略了解下就浅尝辄止, 并没有在项目中正式使用. 直到最近用到Volley. 于是碰到了一个问题.

使用 JsonObjectRequest 发POST请求时, Volley官方说在getParams(xxx) 方法中传递POST参数是无效的, 需要在构造方法中通过 JsonObject 去传递参数, 类似这样

Map<String, String> params = new HashMap<String, String>();
params.put("username","hello_world");
params.put("password", "123456");
params.put("sex","1");

JSONObject paramJsonObject = new JSONObject(params);

JsonObjectRequest mJsonObjectRequest = new JsonObjectRequest(Request.Method.POST,
                url,paramJsonObject,
                successListener, errorListener){
                    //...
                
};

但是后台并不会正常接收到, 除非后台是JsonObject格式去接收并处理客户端这边发出的请求参数. 因为传递到后台的参数是这样的:

{"username":"hello_world","password":"123456","sex":"1"}

我们直接看Volley中 JsonObjectRequest 构造方法的相关源码:

public JsonObjectRequest(int method, String url, JSONObject jsonRequest,
            Listener<JSONObject> listener, ErrorListener errorListener) {
            
        super(method, url, (jsonRequest == null) ? null : jsonRequest.toString(), listener,
                errorListener);
                
}

上面代码可看出, 是直接将装载参数的 JsonObject进行 toString() 处理, 出来的结果就是我们上面所看到的那样. 最后还是回调

public JsonRequest(int method, String url, String requestBody, Listener<T> listener,
            ErrorListener errorListener) {
            
        super(method, url, errorListener);
        mListener = listener;
        mRequestBody = requestBody;
        
}

第二种: getBody(...) 方法
这种方法跟 requestBody 是有关系的. 因为 requestBody 到最后是传值给 mRequestBody. 而 mRequestBody 则在 JsonRequest 中的 getBody(...) 方法被使用:

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

@Override
public byte[] getBody() {
    try {
        return mRequestBody == null ? null : mRequestBody.getBytes(PROTOCOL_CHARSET);
    } catch (UnsupportedEncodingException uee) {
        VolleyLog.wtf("Unsupported Encoding while trying to get the bytes of %s using %s",
                mRequestBody, PROTOCOL_CHARSET);
        return null;
    }
}

一切参数在 getPostBody() 中被返回, 很明显, 这个方法才是最终返回POST参数给请求的.

如果到了这里还不明白, 整个传参的过程, 请直接看 Request 类的这几个方法:

/**
 * Returns the raw POST body to be sent.
 *
 * @throws AuthFailureError In the event of auth failure
 *
 * @deprecated Use {@link #getBody()} instead.
 */
@Deprecated
public byte[] getPostBody() throws AuthFailureError {
    // Note: For compatibility with legacy clients of volley, this implementation must remain
    // here instead of simply calling the getBody() function because this function must
    // call getPostParams() and getPostParamsEncoding() since legacy clients would have
    // overridden these two member functions for POST requests.
    Map<String, String> postParams = getPostParams();
    if (postParams != null && postParams.size() > 0) {
        return encodeParameters(postParams, getPostParamsEncoding());
    }
    return null;
}

/**
 * Returns the raw POST or PUT body to be sent.
 *
 * <p>By default, the body consists of the request parameters in
 * application/x-www-form-urlencoded format. When overriding this method, consider overriding
 * {@link #getBodyContentType()} as well to match the new body format.
 *
 * @throws AuthFailureError in the event of auth failure
 */
public byte[] getBody() throws AuthFailureError {
    Map<String, String> params = getParams();
    if (params != null && params.size() > 0) {
        return encodeParameters(params, getParamsEncoding());
    }
    return null;
}


/**
 * Returns a Map of POST parameters to be used for this request, or null if
 * a simple GET should be used.  Can throw {@link AuthFailureError} as
 * authentication may be required to provide these values.
 *
 * <p>Note that only one of getPostParams() and getPostBody() can return a non-null
 * value.</p>
 * @throws AuthFailureError In the event of auth failure
 *
 * @deprecated Use {@link #getParams()} instead.
 */
@Deprecated
protected Map<String, String> getPostParams() throws AuthFailureError {
    return getParams();
}

/**
 * Returns a Map of parameters to be used for a POST or PUT request.  Can throw
 * {@link AuthFailureError} as authentication may be required to provide these values.
 *
 * <p>Note that you can directly override {@link #getBody()} for custom data.</p>
 *
 * @throws AuthFailureError in the event of auth failure
 */
protected Map<String, String> getParams() throws AuthFailureError {
    return null;
}


/**
 * Converts <code>params</code> into an application/x-www-form-urlencoded encoded string.
 */
private byte[] encodeParameters(Map<String, String> params, String paramsEncoding) {
    StringBuilder encodedParams = new StringBuilder();
    try {
        for (Map.Entry<String, String> entry : params.entrySet()) {
            encodedParams.append(URLEncoder.encode(entry.getKey(), paramsEncoding));
            encodedParams.append('=');
            encodedParams.append(URLEncoder.encode(entry.getValue(), paramsEncoding));
            encodedParams.append('&');
        }
        return encodedParams.toString().getBytes(paramsEncoding);
    } catch (UnsupportedEncodingException uee) {
        throw new RuntimeException("Encoding not supported: " + paramsEncoding, uee);
    }
}

特别是 encodeParameters(...) 方法, 完全看到无论是JsonObject 还是 MAP 装着数据传进来, 最后都是加工成类似 GET 的 "key=value" 的格式. 同时, 我们也明白 StringRequest 如何通过 getParams() 传参的.

这样就好办了, 所以我们在 JsonObjectRequest 的构造方法里直接重写 getBody() 方法就行了:

final String requestBody = "username=hello_world&password=123456&sex=1";

JsonObjectRequest req = new JsonObjectRequest(Request.Method.POST,
                url,
                successListener, errorListener) {

    @Override
    public byte[] getBody() {

        try {
            return requestBody.toString().getBytes("UTF-8");
            
        } catch (Exception e) {
        }
        return null;
    }
};