如何使用java从地图中的HDFS读取数据

Question

我想实现一个程序，我用java编写，在map reduce中，以便它可以在hadoop框架中实现，但我是hadoop的新手应该如何继续。我已经粘贴了程序的基本结构（还有其他更多的类和方法，但我省略了它们，并省略了一些代码以保持简单）我应该如何开始编写驱动程序，映射器和reducer类。

    public class TC{  
    TC tc = new TC();  
    long start =System.currentTimeMillis();  // staring the timer to get running time
    int i=0;  
    int a=0, c=0, g=0, i=0, m=0, s=0, t=0, e=0;  
    String categories[]={"a","c","e","g","i","m","s","t"}; // different categories in the training set 
    Map<String, Integer> all_wordMap=new HamnMap<String, Integer>();  creating a map
    for(i=0;i<categories.length;i++)    
    {     
    String class_file[]=no_of_files("path"+categories[i]);  
    for(int j=0;j<class_file.length;j++){  
    // code block   for counting all distinct words in the files and putting them into the map
    }  
    }  
    int total_words=all_wordMap.size();         // size of the map
    Map<String,String> bvm=new HasnMap<String,String>();    // creating another map         
    for(i=0;i<categories.length;i++)  
    {     
    String class_file[]=tc.no_of_files("path"+categories[i]);  
    for(int j=0;j<class_file.length;j++){                        
    //code block  to create binary vector for each text file
    }  
    }                               
    }            
    String classs = null;  
    String s="path";  // path from where the test files will be read
    String files[]=tc.no_of_files(s);  // no. of test files              
    for(int y=0;y<files.length;y++){                    
    String file1 =files[y];         
    classs=tc.classifier(file1,bvm,all_wordMap);    // calling a method classifier which classify the test file(which class does the test file belong to)  
    System.out.println("The category  is "+classs);  // these are the outputs
    if ("a".equals(classs)){  
    a++;                    
    }
    if ("c".equals(classs)){
    c++;                          
    }             
    if ("e".equals(classs)){
    e++;                            
    }
    if ("g".equals(classs)){
    g++;                          
    }
    if ("in".equals(classs)){
    in++;                        
    }
    if ("mn".equals(classs)){
    mn++;                         
    }
    if ("sh".equals(classs)){
    sh++;                         
    }
    if ("td".equals(classs)){
    td++;                        
    }         
    }
    System.out.println ("a = "+a);  //counting the no. of files of this class
    System.out.println ("c = "+c);  
    System.out.println ("e = "+e);  
    System.out.println ("g = "+g);  
    System.out.println ("in = "+in);  
    System.out.println ("mn = "+mn);  
    System.out.println ("sh = "+sh);  
    System.out.println ("td = "+td);                 
    System.out.println(System.currentTimeMillis() - start);   // stopping the clock
    }