MongoDB Java Development - MongoBoston 2010

Java Development Eliot Horowitz @eliothorowitz MongoBoston September 20, 2010

Java Choices • Straight driver - map like interface • Reﬂection - slow but easy • Morphia - annotation based

Simple Java Mongo m = new Mongo(); DB db = m.getDB( “myapp” ); DBCollection users = db.getCollection( “users” ); BasicDBObject person = new BasicDBObject(); person.put( “name” , “Eliot” ); person.put( “creation_date” , new java.util.Date() users.insert( person );

Morphia public class Person { @Id String username; Date birthDate; @Indexed String state; }

Concurrency • Ideally 1 Mongo instance per JVM • Connection pooling built in • Connections sticky to threads • Force with requestStart/End

WriteConcern • By default writes are ﬁre and forget • Can set WriteConcern on Mongo,DB,DBCollection or per write call • Conﬁgurable fsync, w=, wtimeout= • Will throw exceptions for unique key exceptions, etc... • WriteResult will either cache result or call getLastError if possible.

Types • double,int,long,string, boolean map natively • arrays <=> List • sub-objects <=> Map • date <=> java.util.Date

Custom Type Encoding/Decoding • BSON.addEncodingHook( Class c , Transformer t ); • BSON.addDecodingHook( Class c , Transformer t );

GridFS Mongo m = new Mongo(); DB db = m.getDB( “myapp” ); GridFS fs = new GridFS( db ); GridFSInputFile inFile = fs.createFile( new File( “foo.txt” ) ); in.save(); GridFSDBFile outFile = fs.ﬁndOne( “foo.txt” ); outFile.writeTo( “foo2.txt” );

Hadoop • Coming Soon... • Support for input/output • Suggestions welcome

Mapper public static class TokenizerMapper extends Mapper<Object, BSONObject, Text, IntWritable>{ private ﬁnal static IntWritable one = new IntWritable(1); private Text word = new Text(); public void map(Object key, BSONObject value, Context context ) throws IOException, InterruptedException { StringTokenizer itr = new StringTokenizer(value.get( "x" ).toString()); while (itr.hasMoreTokens()) { word.set(itr.nextToken()); context.write(word, one); } } }

Reducer 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); } }

Running Configuration conf = new Configuration(); MongoConfig.setInput( conf , "localhost" , "test" , "in" ); MongoConfig.setOutput( conf , "localhost" , "test" , "out" ); Job job = new Job(conf, "word count"); job.setJarByClass(WordCount.class); job.setMapperClass(TokenizerMapper.class); job.setCombinerClass(IntSumReducer.class); job.setReducerClass(IntSumReducer.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(IntWritable.class); job.setInputFormatClass( MongoInputFormat.class ); job.setOutputFormatClass( MongoOutputFormat.class ); System.exit(job.waitForCompletion(true) ? 0 : 1);

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MongoDB Java Development - MongoBoston 2010

by Eliot Horowitz on Sep 21, 2010

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