$cd $GOPATH/src/github.com/seaweedfs/seaweedfs/other/java/client
$ mvn install

# build for hadoop3
$cd $GOPATH/src/github.com/seaweedfs/seaweedfs/other/java/hdfs3
$ mvn package
$ ls -al target/seaweedfs-hadoop3-client-4.00.jar

<dependency>
  <groupId>com.seaweedfs</groupId>
  <artifactId>seaweedfs-hadoop3-client</artifactId>
  <version>4.00</version>
</dependency>

# optionally adjust hadoop memory allocation
$ export HADOOP_CLIENT_OPTS="-Xmx4g"

$ cd ${HADOOP_HOME}
# create etc/hadoop/mapred-site.xml, just to satisfy hdfs dfs. skip this if the file already exists.
$ echo "<configuration></configuration>" > etc/hadoop/mapred-site.xml

# on hadoop3
$ bin/hdfs dfs -Dfs.defaultFS=seaweedfs://localhost:8888 \
               -Dfs.seaweedfs.impl=seaweed.hdfs.SeaweedFileSystem \
               -libjars ./seaweedfs-hadoop3-client-4.00.jar \
               -ls /

<configuration>
    <property>
        <name>fs.seaweedfs.impl</name>
        <value>seaweed.hdfs.SeaweedFileSystem</value>
    </property>
    <property>
        <name>fs.defaultFS</name>
        <value>seaweedfs://localhost:8888</value>
    </property>
    <property>
       <name>fs.AbstractFileSystem.seaweedfs.impl</name>
       <value>seaweed.hdfs.SeaweedAbstractFileSystem</value>
    </property>
    <property>
       <name>fs.seaweed.buffer.size</name>
       <value>4194304</value>
    </property>
    <property>
       <name>fs.seaweed.volume.server.access</name>
       <!-- [direct|publicUrl|filerProxy] -->
       <value>direct</value>
    </property>
    <property>
       <name>fs.seaweed.replication</name>
       <value>002</value>
    </property>
</configuration>

# Replication Configuration

SeaweedFS supports configurable replication for data durability. You can set the replication level using the `fs.seaweed.replication` property in `core-site.xml`.

SeaweedFS uses a 3-digit replication string format: (data center)(rack)(volume server) copies.

**Examples:**
- `000` or empty: Use default replication (usually 1 copy)
- `001`: 1 additional copy (2 total copies)
- `002`: 2 additional copies (3 total copies)
- `010`: 1 data center + 1 rack copy (3 total copies)
- `020`: 2 rack copies (3 total copies)

If `fs.seaweed.replication` is not set, SeaweedFS will use the HDFS `dfs.replication` parameter and convert it to SeaweedFS format. If `fs.seaweed.replication` is set to an empty string, SeaweedFS will use the default replication configured on the SeaweedFS filer.

**Configuration:**
```xml
<property>
   <name>fs.seaweed.replication</name>
   <value>002</value>
</property>

# Deploy the SeaweedFS HDFS client jar

Now you can do this:

# Supported HDFS Operations

bin/hdfs dfs -appendToFile README.txt /weedfs/weedfs.txt
bin/hdfs dfs -cat /weedfs/weedfs.txt
bin/hdfs dfs -rm -r /uber
bin/hdfs dfs -chown -R chris:chris /weedfs
bin/hdfs dfs -chmod -R 755 /weedfs
bin/hdfs dfs -copyFromLocal README.txt /weedfs/README.txt.2
bin/hdfs dfs -copyToLocal /weedfs/README.txt.2 .
bin/hdfs dfs -count /weedfs/README.txt.2
bin/hdfs dfs -cp /weedfs/README.txt.2 /weedfs/README.txt.3
bin/hdfs dfs -du -h /weedfs
bin/hdfs dfs -find /weedfs -name "*.txt" -print
bin/hdfs dfs -get /weedfs/weedfs.txt
bin/hdfs dfs -getfacl /weedfs
bin/hdfs dfs -getmerge -nl /weedfs w.txt
bin/hdfs dfs -ls /
bin/hdfs dfs -mkdir /tmp
bin/hdfs dfs -mkdir -p /tmp/x/y
bin/hdfs dfs -moveFromLocal README.txt.2 /tmp/x/
bin/hdfs dfs -mv /tmp/x/y/README.txt.2 /tmp/x/y/README.txt.3
bin/hdfs dfs -mv /tmp/x /tmp/z
bin/hdfs dfs -put README.txt /tmp/z/y/
bin/hdfs dfs -rm /tmp/z/y/*
bin/hdfs dfs -rmdir /tmp/z/y
bin/hdfs dfs -stat /weedfs
bin/hdfs dfs -tail /weedfs/weedfs.txt
bin/hdfs dfs -test -f /weedfs/weedfs.txt
bin/hdfs dfs -text /weedfs/weedfs.txt
bin/hdfs dfs -touchz /weedfs/weedfs.txtx

## Operations Plan to Support

# Notes
## Atomicity
SeaweedFS satisfies the HCFS [requirements](https://hadoop.apache.org/docs/r2.7.2/hadoop-project-dist/hadoop-common/filesystem/introduction.html) that the following operations to be atomic, when using MySql/Postgres/Sqlite database transactions.

1. Creating a file. If the overwrite parameter is false, the check and creation MUST be atomic.
1. Deleting a file.
1. Renaming a file.
1. Renaming a directory.
1. Creating a single directory with mkdir().

Among these, except file or directory renaming, the following operations are all atomic for any filer store.
1. Creating a file
1. Deleting a file
1. Creating a single directory with mkdir().

## No native shared libraries
The SeaweedFS hadoop client is a pure java library. There are no native libraries to install if you already have Hadoop running.

This is different from many other HCFS options. If native shared libraries are needed, these libraries need to be install on all hadoop nodes. This is quite some task.

## Shaded Fat Jar
One of the headache with complicated Java systems is the jar runtime dependency problem, which is resolved by Go's build time dependency resolution. For this SeaweedFS hadoop client, the required jars are mostly shaded and packaged as one fat jar, so there are no extra jar files needed.

## Note
### use `-Djava.net.preferIPv4Stack=true` if possible, see https://github.com/netty/netty/issues/6454
error message:

### See [[Security-Configuration#for-java-grpc]] if you enabled gRpc security.