应为 BEGIN_OBJECT，但在第 1 行第 6 列为 STRING答案

【问题标题】：Expected BEGIN_OBJECT but was STRING at line 1 column 6应为 BEGIN_OBJECT，但在第 1 行第 6 列为 STRING
【发布时间】：2019-04-28 12:34:10
【问题描述】：

我的 java 代码

public class Recipe {

public static class TokenizerMapper  extends Mapper<Object, Text, Text, IntWritable>{

    private final static IntWritable one = new IntWritable(1);
    private Text word = new Text();
    Gson gson = new Gson();
    public void map(Object key, Text value, Context context ) throws IOException, InterruptedException {
        Roo roo=gson.fromJson(value.toString(), Roo.class);

        if (roo.manner_of_death != null) {
        word.set(roo.manner_of_death);
        } else  {
            word.set("none");
        }
        context.write(word, one);
    }
}

public static class IntSumReducer
        extends Reducer<Text,IntWritable,Text,IntWritable> {
    private IntWritable result = new IntWritable();

    public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
        int sum = 0;
        for (IntWritable val : values) {
            sum += val.get();
        }
        result.set(sum);
        context.write(key, result);
    }
}

public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();
    String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();

    if (otherArgs.length != 2) {
        System.err.println("Usage: recipe <in> <out>");
        System.exit(2);
    }
    @SuppressWarnings("deprecation")
    Job job = new Job(conf, "Recipe");

    job.setJarByClass(Recipe.class);
    job.setMapperClass(TokenizerMapper.class);
    job.setCombinerClass(IntSumReducer.class);
    job.setReducerClass(IntSumReducer.class);
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(IntWritable.class);
    FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
    FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
   // FileInputFormat.addInputPath(job, new Path("hdfs://127.0.0.1:9000/in"));
   // FileOutputFormat.setOutputPath(job, new Path("hdfs://127.0.0.1:9000/out"));
    System.exit(job.waitForCompletion(true) ? 0 : 1);
   // job.submit();
}
}

 class Id
{
    public String oid;
}

class Roo
{
    public Id _id ;
    public String resident_status;
    public String month_of_death;
    public String sex;
    public String marital_status; 
    public String manner_of_death;
    public String autopsy;
    public String race;
}

我的 JSON

{
"_id" : ObjectId("5bfc49155fa79a44dca1f9b9"),
"resident_status" : "1",
"month_of_death" : "06",
"sex" : "M",
"marital_status" : "M",
"manner_of_death" : "7",
"autopsy" : "N",
"race" : "02"
}
{                                                    
"_id" : ObjectId("5bfc49155fa79a44dca1f56c"),    
"resident_status" : "1",                         
"month_of_death" : "03",                         
"sex" : "F",                                     
"marital_status" : "D",                          
"manner_of_death" : "7",                         
"autopsy" : "N",                                 
"race" : "01"                                    
}

所有字段都是字符串，除了id

我的错误

18/11/26 18:02:55 信息 mapreduce.Job：任务 ID：尝试_1543189350698_0010_m_000000_0，状态：失败错误：com.google.gson.JsonSyntaxException：java.io.EOFException：第 1 行第 3 列输入结束在 com.google.gson.Gson.fromJson(Gson.java:813)

18/11/26 18:02:55 信息 mapreduce.Job：任务 ID：尝试_1543189350698_0010_m_000001_0，状态：失败错误：com.google.gson.JsonSyntaxException：java.lang.IllegalStateException：预期 BEGIN_OBJECT 但在第 1 行是 STRING

【问题讨论】：

这真的是你的文件吗？包括新线和所有？
顺便说一下，ObjectId("5bfc49155fa79a44dca1f9b9") 不是有效的 JSON。

标签： java hadoop mapreduce gson

【解决方案1】：

当你这样做时，

 class Id
{
    public String oid;
}

class Roo
{
    public Id _id ;

你告诉 Gson 它正在尝试解析这种类型的对象

{                                                    
    "_id" : {
       "oid" : "5bfc49155fa79a44dca1f56c"
    }, 
    ...
}

这不是你所拥有的，而且你也没有有效的 JSON，因为 ObjectId 周围没有引号。

第二个问题 - MapReduce 默认读取单行数据，如果您的输入文件只有两行这样就可以了，但 JSON 仍然应该是有效的

{ "_id" : ... }
{ "_id" : ... }

【讨论】：