背景

由于项目需求要获取某些网页的请求参数信息，get请求的参数拼接在url中，所以可以直接拦截url获得，但是post请求的参数信息存放在body里面，android没有提供方法直接获取，而该网页是其他第三方提供的，不方便修改网页代码来传递参数给android原生这边，所以可以通过js注入的方式来获取。

关键步骤

js代码

核心js代码下载jscore 从文件中读取js代码为字符串，便于后面给webview加载

public class IOUtils {
    public static byte[] readFully(InputStream in) throws IOException {
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        byte[] buffer = new byte[1024];
        for (int count; (count = in.read(buffer)) != -1; ) {
            out.write(buffer, 0, count);
        }
        return out.toByteArray();
    }
}

WebViewClient注入js代码

在页面加载完成回调onPageFinished的时候通过webview.loadUrl()将js代码注入到当前页面

public class InterceptingWebViewClient extends WebViewClient {

    private Context mContext = null;
    private WebView mWebView = null;
    private PostInterceptJavascriptInterface mJSSubmitIntercept;

    public InterceptingWebViewClient(Context context, WebView webView) {
        mContext = context;
        mWebView = webView;
        mJSSubmitIntercept = new PostInterceptJavascriptInterface(this);
        mWebView.addJavascriptInterface(mJSSubmitIntercept, "interception");

    }

    @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
        mNextAjaxRequestContents = null;
        mNextFormRequestContents = null;

        view.loadUrl(url);
        return true;
    }

    @Override
    public void onPageFinished(WebView view, String url) {
        super.onPageFinished(view, url);
        try {
        	String mInterceptHeader = new String(IOUtils.readFully(mContext.getAssets().open("jscore")));
			view.loadUrl("javascript:" + mInterceptHeader);
		}catch (Exception e){
                Log.e("zbm", "js注入失败：" + e);
		}
    }

    private PostInterceptJavascriptInterface.FormRequestContents mNextFormRequestContents = null;

    public void nextMessageIsFormRequest(PostInterceptJavascriptInterface.FormRequestContents formRequestContents) {
        mNextFormRequestContents = formRequestContents;
    }

    private PostInterceptJavascriptInterface.AjaxRequestContents mNextAjaxRequestContents = null;

    public void nextMessageIsAjaxRequest(PostInterceptJavascriptInterface.AjaxRequestContents ajaxRequestContents) {
        mNextAjaxRequestContents = ajaxRequestContents;
    }
}

js与android通信桥梁

当页面有post请求时会回调customAjax与customSubmit接口将请求参数传给原生层。

public class PostInterceptJavascriptInterface {

    private static String mInterceptHeader;
    private InterceptingWebViewClient mWebViewClient;

    public PostInterceptJavascriptInterface(InterceptingWebViewClient webViewClient) {
        mWebViewClient = webViewClient;
    }

    public class FormRequestContents {
        public String method = null;
        public String json = null;
        public String enctype = null;

        public FormRequestContents(String method, String json, String enctype) {
            this.method = method;
            this.json = json;
            this.enctype = enctype;
        }
    }

    public class AjaxRequestContents {
        public String method = null;
        public String body = null;

        public AjaxRequestContents(String method, String body) {
            this.method = method;
            this.body = body;
        }
    }

    @JavascriptInterface
    public void customAjax(final String method, final String body) {
        mWebViewClient.nextMessageIsAjaxRequest(new AjaxRequestContents(method, body));
    }

    @JavascriptInterface
    public void customSubmit(String json, String method, String enctype) {
        mWebViewClient.nextMessageIsFormRequest(
                new FormRequestContents(method, json, enctype));
    }
}