安卓和ResponseCache。请求标头丢失

Question

我正在安卓系统中为HttpUrlConnection实现ResponseCache。一切似乎都很好用。我打电话给

ResponseCache.setDefault(new ResCache());

并且我的ResCache类中的方法可以按预期使用。我遇到的唯一问题是带有请求参数的Map是空的。如果我在android环境之外尝试相同的代码，我将能够看到请求头参数，但在活动内部，所有这些东西都不起作用。以下是该活动的代码。

package com.httptest;

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.CacheRequest;
import java.net.CacheResponse;
import java.net.HttpURLConnection;
import java.net.ResponseCache;
import java.net.URI;
import java.net.URL;
import java.net.URLConnection;
import java.util.List;
import java.util.Map;

import android.app.Activity;
import android.os.Bundle;

public class HttpTest extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        ResponseCache.setDefault(new ResCache());
        HttpURLConnection urlConnection = null;
        try {
        URL url = new URL("http://169.254.198.146//patch/500.php");
        urlConnection = (HttpURLConnection) url
                .openConnection();
        urlConnection.setUseCaches(true);
        urlConnection.setRequestProperty("MY_PROPERTY", "MY_VALUE");
            InputStream in = new BufferedInputStream(
                    urlConnection.getInputStream());
            String aux = readStream(in);
        }catch(Exception e){
            e.printStackTrace();
        }finally {
            urlConnection.disconnect();
        }
    }

    public static String readStream(InputStream in) throws IOException {
        StringBuilder sb = new StringBuilder();
        BufferedReader r = new BufferedReader(new InputStreamReader(in), 1000);
        for (String line = r.readLine(); line != null; line = r.readLine()) {
            sb.append(line);
        }
        in.close();
        return sb.toString();
    }

    public class ResCache extends ResponseCache{

        @Override
        public CacheResponse get(URI arg0, String arg1,
                Map<String, List<String>> arg2) throws IOException {
            System.out.println(arg2);
            return null;
        }

        @Override
        public CacheRequest put(URI uri, URLConnection connection)
                throws IOException {
            return null;
        }
    }
}

在方法ResCache.get(URI，String，Map)中，映射始终为空。我想看看我添加到请求中的参数。顺便说一句，参数都在请求中设置得很好，因为我可以在执行请求时在服务器中读取它们。

同样，这可以在android环境之外工作。

对此有什么帮助吗？

谢谢!

Answer 1

我认为在Android的HttpURLConnection实现中存在一个错误，即响应报头被传递给此方法，而不是请求报头。

我已经在下面的代码中解决了这个问题，尽管我没有在谷歌上搜索到android中的bug的更多细节，但我非常确信android的httpurlconnection实现存在一些问题，因为你可以看到它在非android jvm上工作：

基本上，我通过传递一个VirenRequestHeadersMap而不是传递URLConnection#getRequestProperies()来修复它，使其与从put(...)传递的值保持一致。

@Override
        public CacheRequest put(URI uri, URLConnection connection)
                throws IOException {
            MyPrivateContext context = <>;
            context.setConnection(connection);

            //...
        }

@Override
        public CacheResponse get(URI arg0, String arg1,
                Map<String, List<String>> arg2) throws IOException {
            System.out.println(arg2);

            MyPrivateContext context = <>;
            URLConnection connection = context.getConnection();
            arg2 = new VirenRequestHeadersMap(connection);
            //...
        }

下面是整个VirenRequestHeadersMap类，如果您对它的外观感兴趣的话：

class VirenRequestHeadersMap implements Map<String, List<String>> {

    private final URLConnection mConnection;

    public VirenRequestHeadersMap(URLConnection connection) {
        mConnection = connection;
    }

    public void clear() {
        throw new UnsupportedOperationException();
    }

    public boolean containsKey(Object key) {
        if (key instanceof String) {
            String field = (String) key;
            return mConnection.getRequestProperty(field) != null;
        } else {
            return false;
        }
    }

    public boolean containsValue(Object value) {
        throw new UnsupportedOperationException();
    }

    public Set<Entry<String, List<String>>> entrySet() {
        throw new UnsupportedOperationException();
    }

    public List<String> get(Object key) {
        if (key instanceof String) {
            String field = (String) key;
            String value = mConnection.getRequestProperty(field);
            return value != null ? Collections.singletonList(value) : null;
        } else {
            return null;
        }
    }

    public boolean isEmpty() {
        throw new UnsupportedOperationException();
    }

    public Set<String> keySet() {
        throw new UnsupportedOperationException();
    }

    public List<String> put(String key, List<String> value) {
        throw new UnsupportedOperationException();
    }

    public void putAll(Map<? extends String, ? extends List<String>> value) {
        throw new UnsupportedOperationException();
    }

    public List<String> remove(Object key) {
        throw new UnsupportedOperationException();
    }

    public int size() {
        throw new UnsupportedOperationException();
    }

    public Collection<List<String>> values() {
        throw new UnsupportedOperationException();
    }
}