GFS Client

Description

Implement a simple client for GFS (Google File System, a distributed file system), it provides the following methods:

1. read(filename). Read the file with given filename from GFS.

2. write(filename, content). Write a file with given filename & content to GFS.

There are two private methods that already implemented in the base class:

1. readChunk(filename, chunkIndex). Read a chunk from GFS.

2. writeChunk(filename, chunkIndex, chunkData). Write a chunk to GFS.

To simplify this question, we can assume that the chunk size is_chunkSize_bytes. (In a real world system, it is 64M). The GFS Client's job is splitting a file into multiple chunks (if need) and save to the remote GFS server._chunkSize_will be given in the constructor. You need to call these two private methods to implement read & write methods.

Example

GFSClient(5)
read("a.txt")
>> null
write("a.txt", "World")
>> You don't need to return anything, but you need to call writeChunk("a.txt", 0, "World") to write a 5 bytes chunk to GFS.
read("a.txt")
>> "World"
write("b.txt", "111112222233")
>> You need to save "11111" at chink 0, "22222" at chunk 1, "33" at chunk 2.
write("b.txt", "aaaaabbbbb")
read("b.txt")
>> "aaaaabbbbb"

Solution

/**
* This reference program is provided by @jiuzhang.com
* Copyright is reserved. Please indicate the source for forwarding
*/

/* Definition of BaseGFSClient
 * class BaseGFSClient {
 *     private Map<String, String> chunk_list;
 *     public BaseGFSClient() {}
 *     public String readChunk(String filename, int chunkIndex) {
 *         // Read a chunk from GFS
 *     }
 *     public void writeChunk(String filename, int chunkIndex,
 *                            String content) {
 *         // Write a chunk to GFS
 *     }
 * }
 */
public class GFSClient extends BaseGFSClient {

    public int chunkSize;
    public Map<String, Integer> chunkNum;

    public GFSClient(int chunkSize) {
        // initialize your data structure here
        this.chunkSize = chunkSize;
        this.chunkNum = new HashMap<String, Integer>();
    }

    // @param filename a file name
    // @return conetent of the file given from GFS
    public String read(String filename) {
        // Write your code here
        if (!chunkNum.containsKey(filename))
            return null;

        StringBuffer content = new StringBuffer();

        for (int i = 0; i < chunkNum.get(filename); ++i) {
            String sub_content = readChunk(filename, i);
            if (sub_content != null)
                content.append(sub_content);
        }
        return content.toString();
    }

    // @param filename a file name
    // @param content a string
    // @return void
    public void write(String filename, String content) {
        // Write your code here
        int length = content.length();

        int num = (length - 1) / chunkSize + 1;
        chunkNum.put(filename, num);

        for (int i = 0; i < num; ++i) {
            int start = i * chunkSize;
            int end = i == num -1 ? length : (i + 1) * chunkSize; 
            String sub_content = content.substring(start, end);
            writeChunk(filename, i, sub_content);
        }
    }
}