问题

I'm trying to download readable gtfs real time data (protocol buffer format) using Java so I can view it in a text file.

I tried a couple of approaches:

Approach #1:

URL url = new URL(uri); 
byte[] buffer = new byte[4096];
InputStream is = url.openStream();
byte[] buffer = new byte[4096];
InputStream is = url.openStream();
File file = new File("c:/protobuf_data.txt");
OutputStream output = new FileOutputStream(file);
int numOfBytesReadIntoBuffer = -1;
while((numOfBytesReadIntoBuffer = is.read(buffer)) != -1){
    output.write(buffer, 0, numOfBytesReadIntoBuffer);
}

results (snippet):
099700_L..S20150102*LÊ>0L 1637 8AV/RPY!¯¬œ¥¾¬œ¥"L22S(

Approach #2 (same results as approach #1): import org.apache.commons.io.IOUtils;

URL url = new URL(uri); 
InputStream is = url.openStream();
File file = new File("c:/protobuf_data.txt");
OutputStream output = new FileOutputStream(file);
byte[] bytes = IOUtils.toByteArray(is);
output.write(bytes);

I guess because they both write to the OutputStream the same way, the results are the same.

I also tried the suggestion found here but I just ended up getting errors: When using google protocol buffers to transfer String character,got messy code

I read through protocol buffer docs but I got more confused. https://developers.google.com/protocol-buffers/docs/encoding

I used com.sun.org.apache.xml.internal.security.utils.Base64 but I get an error. Approach #3

URL url = new URL(uri);
InputStream is = url.openStream();

File file = new File("c:/users/Workstation/protobuf_data_bytes.txt");

OutputStream output = new FileOutputStream(file);

byte[] bytes = IOUtils.toByteArray(is);
Init.init();
byte[] decoded_bytes = Base64.decode(bytes);

error:
Exception in thread "main" com.sun.org.apache.xml.internal.security.exceptions.Base64DecodingException: Error while decoding

I also tried using java.util.Base64's wrap method to create an InputStream for decoding Base64 encoded byte stream but the data just got even more mangled.

回答1:

The GTFS-realtime spec now includes code samples for parsing GTFS-realtime data in a variety of languages:

https://developers.google.com/transit/gtfs-realtime/code-samples

It's a good place to start when it comes to parsing GTFS-realtime data in your favorite language.

回答2:

As others mentioned, the gtfs-realtime files are binary and require the special Protocol Buffer compiled code to parse. You're not going to get anywhere with Base64 decoding.

Alternative Method (Command Line + JSON):

However, if you're ONLY trying to parse gtfs-realtime files into a human-readable format, I wrote a standalone tool that converts GTFS-realtime into JSON: https://github.com/harrytruong/gtfs_realtime_json

Just download (no install), and run: gtfs_realtime_json <feed_url>

Here's a sample JSON output.

来源：https://stackoverflow.com/questions/27749975/streaming-gtfs-real-time-data-into-human-readable-format

标签

base64