diff --git a/src/main/java/info/avalon566/shardingscaling/job/DatabaseSyncJob.java b/src/main/java/info/avalon566/shardingscaling/job/DatabaseSyncJob.java
index 8206220f6e85a2772cee6d7de0aa0c25d4a25106..3e5b939eb65a1cefbcb580057e894ddff343931b 100644
--- a/src/main/java/info/avalon566/shardingscaling/job/DatabaseSyncJob.java
+++ b/src/main/java/info/avalon566/shardingscaling/job/DatabaseSyncJob.java
@@ -21,6 +21,7 @@ import info.avalon566.shardingscaling.job.config.SyncConfiguration;
 import lombok.extern.slf4j.Slf4j;
 
 /**
+ * Database sync job.
  * @author avalon566
  */
 @Slf4j
@@ -32,12 +33,15 @@ public class DatabaseSyncJob {
 
     private final RealtimeDataSyncer realtimeDataSyncer;
 
-    public DatabaseSyncJob(SyncConfiguration syncConfiguration) {
+    public DatabaseSyncJob(final SyncConfiguration syncConfiguration) {
         this.syncConfiguration = syncConfiguration;
         this.historyDataSyncer = new HistoryDataSyncer(syncConfiguration);
         this.realtimeDataSyncer = new RealtimeDataSyncer(syncConfiguration);
     }
 
+    /**
+     * Run.
+     */
     public void run() {
         realtimeDataSyncer.preRun();
         historyDataSyncer.run();
diff --git a/src/main/java/info/avalon566/shardingscaling/sync/core/AbstractRunner.java b/src/main/java/info/avalon566/shardingscaling/sync/core/AbstractRunner.java
index 0d2ee96e8dd8f50522434bffd20c4d86b5f7c8e5..4b5425ebdddc573cf0499a649922cc8cbc186aa3 100644
--- a/src/main/java/info/avalon566/shardingscaling/sync/core/AbstractRunner.java
+++ b/src/main/java/info/avalon566/shardingscaling/sync/core/AbstractRunner.java
@@ -17,18 +17,31 @@
 
 package info.avalon566.shardingscaling.sync.core;
 
+import lombok.AccessLevel;
+import lombok.Getter;
+import lombok.Setter;
+
 /**
+ * Abstract runner.
  * @author avalon566
  */
 public abstract class AbstractRunner implements Runner {
 
-    protected boolean running = false;
+    @Setter(AccessLevel.PROTECTED)
+    @Getter(AccessLevel.PROTECTED)
+    private boolean running;
 
+    /**
+     * generic start implement.
+     */
     @Override
     public void start() {
         running = true;
     }
 
+    /**
+     * generic stop implement.
+     */
     @Override
     public void stop() {
         running = false;
diff --git a/src/main/java/info/avalon566/shardingscaling/sync/core/Channel.java b/src/main/java/info/avalon566/shardingscaling/sync/core/Channel.java
index 1285bd62f36d18c402e75dac1b58cf0824b5b94a..201384b8daf6175969280e876b9d9ed27e4935d7 100755
--- a/src/main/java/info/avalon566/shardingscaling/sync/core/Channel.java
+++ b/src/main/java/info/avalon566/shardingscaling/sync/core/Channel.java
@@ -18,10 +18,20 @@
 package info.avalon566.shardingscaling.sync.core;
 
 /**
+ * Channel.
  * @author avalon566
  */
 public interface Channel {
+
+    /**
+     * push a {@code DataRecord} to channel.
+     * @param dataRecord data
+     */
     void pushRecord(Record dataRecord);
 
+    /**
+     * pop a {@code DataRecord} from channel.
+     * @return dataRecord
+     */
     Record popRecord();
-}
\ No newline at end of file
+}
diff --git a/src/main/java/info/avalon566/shardingscaling/sync/jdbc/AbstractJdbcReader.java b/src/main/java/info/avalon566/shardingscaling/sync/jdbc/AbstractJdbcReader.java
index 92e750a769a21e86b63eb9c018bdb25aa5738e8f..80b67f298ae3bd11c350a1942a82767694e6ef06 100755
--- a/src/main/java/info/avalon566/shardingscaling/sync/jdbc/AbstractJdbcReader.java
+++ b/src/main/java/info/avalon566/shardingscaling/sync/jdbc/AbstractJdbcReader.java
@@ -73,7 +73,7 @@ public abstract class AbstractJdbcReader extends AbstractRunner implements Reade
             ps.setFetchDirection(ResultSet.FETCH_REVERSE);
             var rs = ps.executeQuery();
             var metaData = rs.getMetaData();
-            while (running && rs.next()) {
+            while (isRunning() && rs.next()) {
                 var record = new DataRecord(metaData.getColumnCount());
                 record.setType("bootstrap-insert");
                 record.setFullTableName(String.format("%s.%s", conn.getCatalog(), rdbmsConfiguration.getTableName()));
diff --git a/src/main/java/info/avalon566/shardingscaling/sync/jdbc/AbstractJdbcWriter.java b/src/main/java/info/avalon566/shardingscaling/sync/jdbc/AbstractJdbcWriter.java
index 63467bb3d4bb6d2ac5e9c549f73d81f83f019193..22a8b78e10400c4d8b5f310ba4a63ce04c965564 100755
--- a/src/main/java/info/avalon566/shardingscaling/sync/jdbc/AbstractJdbcWriter.java
+++ b/src/main/java/info/avalon566/shardingscaling/sync/jdbc/AbstractJdbcWriter.java
@@ -66,7 +66,7 @@ public abstract class AbstractJdbcWriter extends AbstractRunner implements Write
         var buffer = new ArrayList<DataRecord>(2000);
         var lastFlushTime = System.currentTimeMillis();
         try {
-            while (running) {
+            while (isRunning()) {
                 var record = channel.popRecord();
                 if (null == record) {
                     try {
diff --git a/src/main/java/info/avalon566/shardingscaling/sync/jdbc/Column.java b/src/main/java/info/avalon566/shardingscaling/sync/jdbc/Column.java
index 2b203a4febd258bbef608f0cf5ef645f73f939ad..47f56ded7de9b7c183c55ae8a495b2e949f942f5 100755
--- a/src/main/java/info/avalon566/shardingscaling/sync/jdbc/Column.java
+++ b/src/main/java/info/avalon566/shardingscaling/sync/jdbc/Column.java
@@ -21,11 +21,13 @@ import lombok.AllArgsConstructor;
 import lombok.Data;
 
 /**
+ * Column.
  * @author avalon566
  */
 @Data
 @AllArgsConstructor
 public class Column {
     private Object value;
+
     private boolean updated;
-}
\ No newline at end of file
+}
diff --git a/src/main/java/info/avalon566/shardingscaling/sync/jdbc/ColumnMetaData.java b/src/main/java/info/avalon566/shardingscaling/sync/jdbc/ColumnMetaData.java
index e54e0cc5de95c17ca01fbdd1281f61f46a3632eb..6a9d5003da949872a3815d885e3b3b83d40ab0e3 100644
--- a/src/main/java/info/avalon566/shardingscaling/sync/jdbc/ColumnMetaData.java
+++ b/src/main/java/info/avalon566/shardingscaling/sync/jdbc/ColumnMetaData.java
@@ -20,6 +20,7 @@ package info.avalon566.shardingscaling.sync.jdbc;
 import lombok.Data;
 
 /**
+ * Column meta data.
  * @author avalon566
  */
 @Data
diff --git a/src/main/java/info/avalon566/shardingscaling/sync/jdbc/DataRecord.java b/src/main/java/info/avalon566/shardingscaling/sync/jdbc/DataRecord.java
index 627b4bf89a1e101a9121cd6950252d86b4bedb61..a5ea4a42c9086ac90e1f58d9fe45c3ad769aec65 100755
--- a/src/main/java/info/avalon566/shardingscaling/sync/jdbc/DataRecord.java
+++ b/src/main/java/info/avalon566/shardingscaling/sync/jdbc/DataRecord.java
@@ -24,32 +24,54 @@ import java.util.ArrayList;
 import java.util.List;
 
 /**
+ * Data record.
  * @author avalon566
  */
 @Data
 public class DataRecord implements Record {
+
     private String type;
+
     private String tableName;
+
     private String fullTableName;
+
     private final List<Column> columns;
 
-    public DataRecord(int columnCount) {
-        columns = new ArrayList<Column>(columnCount);
+    public DataRecord(final int columnCount) {
+        columns = new ArrayList<>(columnCount);
     }
 
-    public void addColumn(Column data) {
+    /**
+     * Add a column to record.
+     * @param data column
+     */
+    public void addColumn(final Column data) {
         columns.add(data);
     }
 
+    /**
+     * Return column count.
+     * @return count
+     */
     public int getColumnCount() {
         return columns.size();
     }
 
-    public Column getColumn(int index) {
+    /**
+     * Get column by index.
+     * @param index of column
+     * @return column
+     */
+    public Column getColumn(final int index) {
         return columns.get(index);
     }
 
+    /**
+     * Get table name.
+     * @return tableName
+     */
     public String getTableName() {
         return fullTableName.split("\\.")[1];
     }
-}
\ No newline at end of file
+}
diff --git a/src/main/java/info/avalon566/shardingscaling/sync/jdbc/DbMetaDataUtil.java b/src/main/java/info/avalon566/shardingscaling/sync/jdbc/DbMetaDataUtil.java
index 785c7bd35b7e67717b927723b358b36170be5d22..003f9326b3a6db3241aaa2ee775100749bb3f0cb 100755
--- a/src/main/java/info/avalon566/shardingscaling/sync/jdbc/DbMetaDataUtil.java
+++ b/src/main/java/info/avalon566/shardingscaling/sync/jdbc/DbMetaDataUtil.java
@@ -26,12 +26,15 @@ import lombok.var;
 
 import java.sql.DriverManager;
 import java.sql.ResultSet;
+import java.sql.SQLException;
 import java.util.ArrayList;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.concurrent.ExecutionException;
 
 /**
+ * Database meta util.
+ *
  * @author avalon566
  */
 @Slf4j
@@ -51,14 +54,14 @@ public final class DbMetaDataUtil {
 
     private LoadingCache<String, List<ColumnMetaData>> cmdCache;
 
-    public DbMetaDataUtil(RdbmsConfiguration rdbmsConfiguration) {
+    public DbMetaDataUtil(final RdbmsConfiguration rdbmsConfiguration) {
         this.rdbmsConfiguration = rdbmsConfiguration;
 
         pksCache = CacheBuilder.newBuilder()
                 .maximumSize(64)
                 .build(new CacheLoader<String, List<String>>() {
                     @Override
-                    public List<String> load(String key) {
+                    public List<String> load(final String key) {
                         return getPrimaryKeysInternal(key);
                     }
                 });
@@ -67,13 +70,19 @@ public final class DbMetaDataUtil {
                 .maximumSize(64)
                 .build(new CacheLoader<String, List<ColumnMetaData>>() {
                     @Override
-                    public List<ColumnMetaData> load(String key) {
+                    public List<ColumnMetaData> load(final String key) {
                         return getColumNamesInternal(key);
                     }
                 });
     }
 
-    public List<String> getPrimaryKeys(String tableName) {
+    /**
+     * Get primary key column name by table name.
+     *
+     * @param tableName table name
+     * @return list of table name
+     */
+    public List<String> getPrimaryKeys(final String tableName) {
         try {
             return pksCache.get(tableName);
         } catch (ExecutionException e) {
@@ -81,7 +90,7 @@ public final class DbMetaDataUtil {
         }
     }
 
-    private List<String> getPrimaryKeysInternal(String tableName) {
+    private List<String> getPrimaryKeysInternal(final String tableName) {
         try {
             try (var connection = DriverManager.getConnection(rdbmsConfiguration.getJdbcUrl(), rdbmsConfiguration.getUsername(), rdbmsConfiguration.getPassword())) {
                 var rs = connection.getMetaData().getPrimaryKeys(connection.getCatalog(), null, tableName);
@@ -91,11 +100,16 @@ public final class DbMetaDataUtil {
                 }
                 return primaryKeys;
             }
-        } catch (Exception e) {
+        } catch (SQLException e) {
             throw new RuntimeException("getTableNames error", e);
         }
     }
 
+    /**
+     * Get all table names in current database.
+     *
+     * @return list of table name
+     */
     public List<String> getTableNames() {
         try {
             try (var connection = DriverManager.getConnection(rdbmsConfiguration.getJdbcUrl(), rdbmsConfiguration.getUsername(), rdbmsConfiguration.getPassword())) {
@@ -106,12 +120,18 @@ public final class DbMetaDataUtil {
                 }
                 return tableNames;
             }
-        } catch (Exception e) {
+        } catch (SQLException e) {
             throw new RuntimeException("getTableNames error", e);
         }
     }
 
-    public List<ColumnMetaData> getColumNames(String tableName) {
+    /**
+     * Get all column meta data by table name.
+     *
+     * @param tableName table name
+     * @return list of column meta data
+     */
+    public List<ColumnMetaData> getColumNames(final String tableName) {
         try {
             return cmdCache.get(tableName);
         } catch (ExecutionException e) {
@@ -119,36 +139,38 @@ public final class DbMetaDataUtil {
         }
     }
 
-    public List<ColumnMetaData> getColumNamesInternal(String tableName) {
+    private List<ColumnMetaData> getColumNamesInternal(final String tableName) {
         try {
             try (var connection = DriverManager.getConnection(rdbmsConfiguration.getJdbcUrl(), rdbmsConfiguration.getUsername(), rdbmsConfiguration.getPassword())) {
                 var result = new ArrayList<ColumnMetaData>();
-                try (ResultSet resultSet = connection.getMetaData().getColumns(connection.getCatalog(), connection.getSchema(), tableName, "%")) {
-                    while (resultSet.next()) {
-                        var columnMetaData = new ColumnMetaData();
-                        columnMetaData.setColumnName(resultSet.getString(COLUMN_NAME));
-                        columnMetaData.setColumnType(resultSet.getInt(DATA_TYPE));
-                        columnMetaData.setColumnTypeName(resultSet.getString(TYPE_NAME));
-                        result.add(columnMetaData);
-                    }
+                ResultSet resultSet = connection.getMetaData().getColumns(connection.getCatalog(), connection.getSchema(), tableName, "%");
+                while (resultSet.next()) {
+                    var columnMetaData = new ColumnMetaData();
+                    columnMetaData.setColumnName(resultSet.getString(COLUMN_NAME));
+                    columnMetaData.setColumnType(resultSet.getInt(DATA_TYPE));
+                    columnMetaData.setColumnTypeName(resultSet.getString(TYPE_NAME));
+                    result.add(columnMetaData);
                 }
                 return result;
             }
-        } catch (Exception e) {
+        } catch (SQLException e) {
             throw new RuntimeException("getTableNames error", e);
         }
     }
 
-    public static int findColumnIndex(List<ColumnMetaData> metaData, String columnName) {
-        try {
-            for (int i = 0; i < metaData.size(); i++) {
-                if (metaData.get(i).getColumnName().equals(columnName)) {
-                    return i;
-                }
+    /**
+     * Find column index by column name.
+     *
+     * @param metaData   meta data list
+     * @param columnName table name
+     * @return index
+     */
+    public static int findColumnIndex(final List<ColumnMetaData> metaData, final String columnName) {
+        for (int i = 0; i < metaData.size(); i++) {
+            if (metaData.get(i).getColumnName().equals(columnName)) {
+                return i;
             }
-            return -1;
-        } catch (Exception e) {
-            throw new RuntimeException("findColumnIndex error", e);
         }
+        return -1;
     }
 }
diff --git a/src/main/java/info/avalon566/shardingscaling/sync/mysql/binlog/packet/AbstractPacket.java b/src/main/java/info/avalon566/shardingscaling/sync/mysql/binlog/packet/AbstractPacket.java
index 3ba9ffb9695f32b4e957e86d74713a52cd0c3b1f..8a1e41828121fb70db1f5e0f45cf9ffccd46a32f 100644
--- a/src/main/java/info/avalon566/shardingscaling/sync/mysql/binlog/packet/AbstractPacket.java
+++ b/src/main/java/info/avalon566/shardingscaling/sync/mysql/binlog/packet/AbstractPacket.java
@@ -35,11 +35,19 @@ import lombok.Data;
 public abstract class AbstractPacket implements Packet {
     private byte sequenceNumber;
 
+    /**
+     * empty implement method,throw {@code UnsupportedOperationException}.
+     * @param data buffer
+     */
     @Override
     public void fromByteBuf(final ByteBuf data) {
         throw new UnsupportedOperationException();
     }
 
+    /**
+     * empty implement method,throw {@code UnsupportedOperationException}.
+     * @return data buffer
+     */
     @Override
     public ByteBuf toByteBuf() {
         throw new UnsupportedOperationException();
diff --git a/src/main/java/info/avalon566/shardingscaling/sync/mysql/binlog/packet/binlog/ColumnTypes.java b/src/main/java/info/avalon566/shardingscaling/sync/mysql/binlog/packet/binlog/ColumnTypes.java
index 6a184160ed7c143cbfc66e71e6d48e612f70321f..cf1e4174d390016987ba0146c2a3d2666e9f5aea 100644
--- a/src/main/java/info/avalon566/shardingscaling/sync/mysql/binlog/packet/binlog/ColumnTypes.java
+++ b/src/main/java/info/avalon566/shardingscaling/sync/mysql/binlog/packet/binlog/ColumnTypes.java
@@ -18,6 +18,7 @@
 package info.avalon566.shardingscaling.sync.mysql.binlog.packet.binlog;
 
 /**
+ * Mysql column types.
  * @author avalon566
  */
 public final class ColumnTypes {
diff --git a/src/test/java/info/avalon566/shardingscaling/sync/mysql/binlog/codec/MySQLBinlogEventPacketDecoderTest.java b/src/test/java/info/avalon566/shardingscaling/sync/mysql/binlog/codec/MySQLBinlogEventPacketDecoderTest.java
index 5a3599ab319cf8d6c1960c90d32c3d4a0b90bf41..e7d12ec7a7b2a188349b5e334447798cb1e214e6 100644
--- a/src/test/java/info/avalon566/shardingscaling/sync/mysql/binlog/codec/MySQLBinlogEventPacketDecoderTest.java
+++ b/src/test/java/info/avalon566/shardingscaling/sync/mysql/binlog/codec/MySQLBinlogEventPacketDecoderTest.java
@@ -50,7 +50,7 @@ public class MySQLBinlogEventPacketDecoderTest {
     
     @Before
     public void setUp() throws Exception {
-        binlogEventPacketDecoder = new MySQLBinlogEventPacketDecoder();
+        binlogEventPacketDecoder = new MySQLBinlogEventPacketDecoder(0);
         binlogContext = ReflectionUtil.getFieldValueFromClass(binlogEventPacketDecoder, "binlogContext", BinlogContext.class);
         binlogContext.setChecksumLength(4);
     }