因为datax目前不支持写入数据到kafka中，因此本文主要介绍如何基于DataX自定义KafkaWriter，用来同步数据到kafka中。本文偏向实战，datax插件开发理论宝典请参考官方文档：

https://github.com/alibaba/DataX/blob/master/dataxPluginDev.md。

首先我们需要克隆datax源码到本地，此处不再赘述。然后使用开发工具打开datax项目，项目结构如下：

可以看到不论是reader还是writer都是独立的项目，所以我们也需要新建kafkawriter的项目。可以直接新建，也可以复制一个现有的writer项目然后进行修改。注意包结构需要与现有的writer保持一致，如下所示：

基本上所有插件的目录结构都是这样，main文件夹下面分为三个目录，分别为assembly、java、resources。其中assembly下面主要用来存放打包文件，java则是存放我们的代码，resources中存放插件相关的配置信息。

创建完kafkawriter项目之后，需要在datax的pom文件中添加上我们的插件，如下图所示：然后我们需要在datax的打包文件中加入我们的kafkawriter插件，如下图所示：接下来从上到下依次介绍各文件的内容。

<assemblyxmlns="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.0 http://maven.apache.org/xsd/assembly-1.1.0.xsd"><id></id><formats><format>dir</format></formats><includeBaseDirectory>false</includeBaseDirectory><fileSets><fileSet><directory>src/main/resources</directory><includes><include>plugin.json</include><include>plugin_job_template.json</include></includes><outputDirectory>plugin/writer/kafkawriter</outputDirectory></fileSet><fileSet><directory>target/</directory><includes><include>kafkawriter-0.0.1-SNAPSHOT.jar</include></includes><outputDirectory>plugin/writer/kafkawriter</outputDirectory></fileSet></fileSets><dependencySets><dependencySet><useProjectArtifact>false</useProjectArtifact><outputDirectory>plugin/writer/kafkawriter/libs</outputDirectory><scope>runtime</scope></dependencySet></dependencySets></assembly>

该文件主要配置插件的打包信息，基本上所有的插件内容也都是类似的，主要修改的地方如图所示：

如果我们想自定义s3的writer，也只需要修改图中所标识的几个地方。

• KafkaWriter

该类为我们实现写入数据到kafka的主要逻辑实现类，其主要结构可以参照上文中提到的datax官方文档，代码示例如下，每个地方的处理逻辑可以参考代码中的注释。

package com.alibaba.datax.plugin.writer.kafkawriter;import com.alibaba.datax.common.element.Column;import com.alibaba.datax.common.element.Record;import com.alibaba.datax.common.exception.DataXException;import com.alibaba.datax.common.plugin.RecordReceiver;import com.alibaba.datax.common.spi.Writer;import com.alibaba.datax.common.util.Configuration;import com.alibaba.datax.plugin.writer.kafkawriter.entity.*;import com.alibaba.fastjson2.JSON;import com.alibaba.fastjson2.JSONObject;import com.alibaba.fastjson2.JSONWriter;import org.apache.commons.lang3.ObjectUtils;import org.apache.commons.lang3.StringUtils;import org.apache.kafka.clients.admin.AdminClient;import org.apache.kafka.clients.admin.ListTopicsResult;import org.apache.kafka.clients.admin.NewTopic;import org.apache.kafka.clients.producer.KafkaProducer;import org.apache.kafka.clients.producer.Producer;import org.apache.kafka.clients.producer.ProducerRecord;import org.apache.kafka.common.header.internals.RecordHeader;import org.apache.kafka.common.header.internals.RecordHeaders;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import java.io.IOException;import java.nio.charset.StandardCharsets;import java.util.*;//首先自定义的writer需要继承Writer类public class KafkaWriter extends Writer {//创建Job类继承Writer.Jobpublic static class Job extends Writer.Job {private static final Logger logger = LoggerFactory.getLogger(Job.class);//存放同步任务的配置信息private Configuration conf = null;//重写split方法，任务切分逻辑，writer切分主要依据上游reader任务的切分数@Overridepublic List<Configuration> split(int mandatoryNumber) {List<Configuration> configurations = new ArrayList<Configuration>(mandatoryNumber);for (int i = 0; i < mandatoryNumber; i++) {configurations.add(conf);}return configurations;}//重写init方法，进行相关的初始化操作@Overridepublic void init() {//获取同步任务相关的配置this.conf = super.getPluginJobConf();logger.info("kafka writer params:{}", conf.toJSON());//校验配置中的必要参数this.validateParameter();}private void validateParameter() {this.conf.getNecessaryValue(Key.BOOTSTRAP_SERVERS, KafkaWriterErrorCode.REQUIRED_VALUE);this.conf.getNecessaryValue(Key.TOPIC, KafkaWriterErrorCode.REQUIRED_VALUE);this.conf.getNecessaryValue(Key.COLUMN, KafkaWriterErrorCode.REQUIRED_VALUE);}//重写destroy方法，主要用来处理数据同步任务结束之后需要收尾的事情，比如删除同步过程中可能产生的临时文件，关闭连接等@Overridepublic void destroy() {}}public static class Task extends Writer.Task {private static final Logger logger = LoggerFactory.getLogger(Task.class);//存放同步任务的配置信息private Configuration conf;//存放同步的数据表列信息private List<String> columns;//保存kafka的相关配置private Properties properties;//定义kafka生产者private Producer<String, String> producer;//数据同步的目标topicprivate String topic;//kafka消息header（如果单纯同步数据，不需要定义消息头，可以删除该字段）private RecordHeaders recordHeaders = new RecordHeaders();//控制消息是否格式化为cdc格式（如果单纯同步数据，不需要定义特殊的消息格式，可以删除该字段及下面代码的相关逻辑）private Boolean cdcValue = false;//源表主键信息（如果单纯同步数据，不需要定义特殊的消息格式，可以删除该字段及下面代码的相关逻辑）private List<String> primaryKeys;//init（）方法主要对任务配置的解析赋值以及一些认证处理逻辑@Overridepublic void init() {this.conf = super.getPluginJobConf();//kerberos逻辑处理，如果开启kerberos认证可以参考，如果没有可以删除String haveKerberos = conf.getUnnecessaryValue(Key.HAVE_KERBEROS, "false", null);if (StringUtils.isNotBlank(haveKerberos) && haveKerberos.equalsIgnoreCase("true")) {String kerberosPrincipal = conf.getString(Key.KERBEROS_PRINCIPAL);String kerberosKrb5ConfigPath = conf.getString(Key.KERBEROS_KRB5CONFIG_PATH);String kerberosKeytabFilePath = conf.getString(Key.KERBEROS_KEYTABFILE_PATH);if (StringUtils.isBlank(kerberosPrincipal) || StringUtils.isBlank(kerberosKrb5ConfigPath) || StringUtils.isBlank(kerberosKeytabFilePath)) {throw new DataXException(KafkaWriterErrorCode.KERBEROS_VALUE, KafkaWriterErrorCode.KERBEROS_VALUE.getDescription());}try {LoginUtil.securityPrepare(kerberosPrincipal, kerberosKrb5ConfigPath, kerberosKeytabFilePath);} catch (IOException e) {throw new DataXException(KafkaWriterErrorCode.KERBEROS_AUTH, KafkaWriterErrorCode.KERBEROS_AUTH.getDescription());}}//初始化message header，此处是业务特定需求需要给同步到kafka中的message加上header，如果有（特殊的处理逻辑，如果不需要可以删除）if (StringUtils.isNotBlank(conf.getString(Key.KAFKAHEADER))) {JSONObject jsonObject = JSONObject.parseObject(conf.getString(Key.KAFKAHEADER));jsonObject.forEach((key, value) -> {if (StringUtils.isBlank(String.valueOf(value)) || String.valueOf(value).equals("null")) {RecordHeader recordHeader = new RecordHeader(key, null);recordHeaders.add(recordHeader);} else {RecordHeader recordHeader = new RecordHeader(key, String.valueOf(value).getBytes(StandardCharsets.UTF_8));recordHeaders.add(recordHeader);}});}//控制message格式的开关if (conf.getBool(Key.CDCVALUE) != null) {this.cdcValue = conf.getBool(Key.CDCVALUE);}//获取列属性并保存this.columns = conf.getList(Key.COLUMN, String.class);//获取源表主键信息并保存this.primaryKeys = conf.getList(Key.PRIMARYKEYS, String.class);//获取配置的目标topicthis.topic = conf.getNecessaryValue(Key.TOPIC, KafkaWriterErrorCode.REQUIRED_VALUE);//设置kafka配置信息properties = new Properties();properties.put("bootstrap.servers", conf.getString(Key.BOOTSTRAP_SERVERS));properties.put("key.serializer", conf.getUnnecessaryValue(Key.KEY_SERIALIZER, "org.apache.kafka.common.serialization.StringSerializer", null));properties.put("value.serializer", conf.getUnnecessaryValue(Key.VALUE_SERIALIZER, "org.apache.kafka.common.serialization.StringSerializer", null));properties.put("acks", conf.getUnnecessaryValue(Key.ACK, "0", null));properties.put("retries", conf.getUnnecessaryValue(Key.RETRIES, "0", null));properties.put("batch.size", conf.getUnnecessaryValue(Key.BATCH_SIZE, "16384", null));producer = new KafkaProducer<String, String>(properties);}//prepare() 方法主要用来进行一些同步前的准备工作，比如创建目标topic@Overridepublic void prepare() {//创建目标topicif (Boolean.valueOf(conf.getUnnecessaryValue(Key.NO_TOPIC_CREATE, "false", null))) {ListTopicsResult topicsResult = AdminClient.create(properties).listTopics();try {if (!topicsResult.names().get().contains(this.topic)) {NewTopic newTopic = new NewTopic(this.topic,Integer.valueOf(conf.getUnnecessaryValue(Key.TOPIC_NUM_PARTITION, "1", null)),Short.valueOf(conf.getUnnecessaryValue(Key.TOPIC_REPLICATION_FACTOR, "1", null)));AdminClient.create(properties).createTopics(Arrays.asList(newTopic));}} catch (Exception e) {throw new DataXException(KafkaWriterErrorCode.CREATE_TOPIC, KafkaWriterErrorCode.REQUIRED_VALUE.getDescription());}}//特殊处理，数据开始同步前，首先发送一条特定格式的消息（特殊处理逻辑，可以参考，不需要可以删除）if (cdcValue) {FirstCdcValueTemplate firstCdcValueTemplate = new FirstCdcValueTemplate();JSONObject tableId = new JSONObject();//tableId的值为topic名称tableId.put("tableName", this.conf.getString(Key.TOPIC));firstCdcValueTemplate.setTableId(tableId);SchemaTemplate schemaTemplate = new SchemaTemplate();schemaTemplate.setColumns(buildFirstMessageColumns());if (this.primaryKeys != null && this.primaryKeys.size() > 0) {schemaTemplate.setPrimaryKeys(this.primaryKeys);} else {schemaTemplate.setPrimaryKeys(Arrays.asList());}schemaTemplate.setPartitionKeys(Arrays.asList());schemaTemplate.setOptions(new JSONObject());firstCdcValueTemplate.setSchema(schemaTemplate);producer.send(new ProducerRecord<String, String>(this.conf.getString(Key.TOPIC),null, null, null, JSON.toJSONString(firstCdcValueTemplate, JSONWriter.Feature.WriteMapNullValue), this.recordHeaders));}}//依次写入数据到kafka@Overridepublic void startWrite(RecordReceiver lineReceiver) {Record record = null;while ((record = lineReceiver.getFromReader()) != null) {producer.send(new ProducerRecord<String, String>(this.conf.getString(Key.TOPIC),null, null, null, buildMessage(record), this.recordHeaders));}}//进行收尾工作，关闭生产者客户端@Overridepublic void destroy() {if (ObjectUtils.isNotEmpty(this.producer)) {this.producer.close();}}//组装特殊message格式private List<ColumnTemplate> buildFirstMessageColumns() {List<ColumnTemplate> columnTemplates = new ArrayList<>();JSONObject jsonObject = JSONObject.parseObject(conf.getString(Key.KAFKAHEADER));List<HeaderSchemaTemplate> schemaJson = jsonObject.getList("schemaJson", HeaderSchemaTemplate.class);for (HeaderSchemaTemplate temp : schemaJson) {ColumnTemplate columnTemplate = new ColumnTemplate();columnTemplate.setName(temp.getName());columnTemplate.setType(temp.getType());columnTemplates.add(columnTemplate);}return columnTemplates;}//组装message格式private String buildMessage(Record record) {JSONObject jo = new JSONObject();for (int i = 0; i < columns.size(); i++) {String columnName = columns.get(i);Column columnValue = record.getColumn(i);if (!Objects.isNull(columnValue)) {if (Objects.isNull(columnValue.getRawData())) {jo.put(columnName, null);} else {switch (columnValue.getType()) {case INT:jo.put(columnName, columnValue.asBigInteger());break;case BOOL:jo.put(columnName, columnValue.asBoolean());break;case LONG:jo.put(columnName, columnValue.asLong());break;case DOUBLE:jo.put(columnName, columnValue.asDouble());break;default:jo.put(columnName, columnValue.asString());}}} else {jo.put(columnName, null);}}if (cdcValue) {ValueTemplate valueTemplate = new ValueTemplate();valueTemplate.setBefore(null);valueTemplate.setAfter(jo);valueTemplate.setOp("c");return JSON.toJSONString(valueTemplate, JSONWriter.Feature.WriteMapNullValue);} else {return jo.toJSONString();}}}}

可以注意到上文中的Task内部类中定义了几个特殊的变量：recordHeaders、cdcValue、primaryKeys，这几个变量主要是用来定义特殊的kafka消息格式，比如当前代码的逻辑是要将消息转换为CDC相关的格式，所以做了额外处理。可以参考该思路，如果有其他的类似的需求，也可以通过任务配置传递进来，然后构建消息的时候进行处理。

• KafkaWriterErrorCode

定义错误码，抛出异常的时候用来提示。

package com.alibaba.datax.plugin.writer.kafkawriter;import com.alibaba.datax.common.spi.ErrorCode;public enum KafkaWriterErrorCode implements ErrorCode {REQUIRED_VALUE("KafkaWriter-00", "您缺失了必须填写的参数值."),KERBEROS_VALUE("KafkaWriter-02", "您缺失了必须填写的kerberos参数值."),KERBEROS_AUTH("KafkaWriter-03", "kerberos认证失败"),CREATE_TOPIC("KafkaWriter-01", "写入数据前检查topic或是创建topic失败.");private final String code;private final String description;private KafkaWriterErrorCode(String code, String description) {this.code = code;this.description = description;}@Overridepublic String getCode() {return this.code;}@Overridepublic String getDescription() {return this.description;}@Overridepublic String toString() {return String.format("Code:[%s], Description:[%s].", this.code,this.description);}}

• Key

该类定义数据同步任务配置文件中的Key

package com.alibaba.datax.plugin.writer.kafkawriter;public class Key {public static final String BOOTSTRAP_SERVERS = "bootstrapServers";public static final String TOPIC = "topic";public static final String KEY_SERIALIZER = "keySerializer";public static final String VALUE_SERIALIZER = "valueSerializer";public static final String COLUMN = "column";public static final String ACK = "ack";public static final String BATCH_SIZE = "batchSize";public static final String RETRIES = "retries";public static final String NO_TOPIC_CREATE = "noTopicCreate";public static final String TOPIC_NUM_PARTITION = "topicNumPartition";public static final String TOPIC_REPLICATION_FACTOR = "topicReplicationFactor";//是否开启kerberos认证public static final String HAVE_KERBEROS = "haveKerberos";public static final String KERBEROS_KEYTABFILE_PATH = "kerberosKeytabFilePath";public static final String KERBEROS_PRINCIPAL = "kerberosPrincipal";public static final String KERBEROS_KRB5CONFIG_PATH = "kerberosKrb5ConfigPath";public static final String KAFKAHEADER = "kafkaHeader";public static final String CDCVALUE = "cdcValue";public static final String PRIMARYKEYS = "primarykeys";}

• LoginUtil

该类主要是定义了kerberos认证的相关逻辑，可以参考

package com.alibaba.datax.plugin.writer.kafkawriter;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import java.io.File;import java.io.FileWriter;import java.io.IOException;public class LoginUtil {private static final Logger LOG = LoggerFactory.getLogger(LoginUtil.class);public enum Module {KAFKA("KafkaClient"), ZOOKEEPER("Client");private String name;private Module(String name) {this.name = name;}public String getName() {return name;}}/*** line operator string*/private static final String LINE_SEPARATOR = System.getProperty("line.separator");/*** jaas file postfix*/private static final String JAAS_POSTFIX = ".jaas.conf";/*** is IBM jdk or not*/private static final boolean IS_IBM_JDK = System.getProperty("java.vendor").contains("IBM");/*** IBM jdk login module*/private static final String IBM_LOGIN_MODULE = "com.ibm.security.auth.module.Krb5LoginModule required";/*** oracle jdk login module*/private static final String SUN_LOGIN_MODULE = "com.sun.security.auth.module.Krb5LoginModule required";/*** Zookeeper quorum principal.*/public static final String ZOOKEEPER_AUTH_PRINCIPAL = "zookeeper.server.principal";/*** java security krb5 file path*/public static final String JAVA_SECURITY_KRB5_CONF = "java.security.krb5.conf";/*** java security login file path*/public static final String JAVA_SECURITY_LOGIN_CONF = "java.security.auth.login.config";/*** 设置jaas.conf文件** @param principal* @param keytabPath* @throws IOException*/public static void setJaasFile(String principal, String keytabPath)throws IOException {String jaasPath =new File(System.getProperty("java.io.tmpdir")) + File.separator + System.getProperty("user.name")+ JAAS_POSTFIX;// windows路径下分隔符替换jaasPath = jaasPath.replace("\\", "\\\\");// 删除jaas文件deleteJaasFile(jaasPath);writeJaasFile(jaasPath, principal, keytabPath);System.setProperty(JAVA_SECURITY_LOGIN_CONF, jaasPath);}/*** 设置zookeeper服务端principal** @param zkServerPrincipal* @throws IOException*/public static void setZookeeperServerPrincipal(String zkServerPrincipal) throws IOException {System.setProperty(ZOOKEEPER_AUTH_PRINCIPAL, zkServerPrincipal);String ret = System.getProperty(ZOOKEEPER_AUTH_PRINCIPAL);if (ret == null) {throw new IOException(ZOOKEEPER_AUTH_PRINCIPAL + " is null.");}if (!ret.equals(zkServerPrincipal)) {throw new IOException(ZOOKEEPER_AUTH_PRINCIPAL + " is " + ret + " is not " + zkServerPrincipal + ".");}}/*** 设置krb5文件** @param krb5ConfFile* @throws IOException*/public static void setKrb5Config(String krb5ConfFile) throws IOException {System.setProperty(JAVA_SECURITY_KRB5_CONF, krb5ConfFile);String ret = System.getProperty(JAVA_SECURITY_KRB5_CONF);if (ret == null) {throw new IOException(JAVA_SECURITY_KRB5_CONF + " is null.");}if (!ret.equals(krb5ConfFile)) {throw new IOException(JAVA_SECURITY_KRB5_CONF + " is " + ret + " is not " + krb5ConfFile + ".");}}/*** 写入jaas文件** @throws IOException 写文件异常*/private static void writeJaasFile(String jaasPath, String principal, String keytabPath)throws IOException {FileWriter writer = new FileWriter(new File(jaasPath));try {writer.write(getJaasConfContext(principal, keytabPath));writer.flush();} catch (IOException e) {throw new IOException("Failed to create jaas.conf File");} finally {writer.close();}}private static void deleteJaasFile(String jaasPath) throws IOException {File jaasFile = new File(jaasPath);if (jaasFile.exists()) {if (!jaasFile.delete()) {throw new IOException("Failed to delete exists jaas file.");}}}private static String getJaasConfContext(String principal, String keytabPath) {Module[] allModule = Module.values();StringBuilder builder = new StringBuilder();for (Module modlue : allModule) {builder.append(getModuleContext(principal, keytabPath, modlue));}return builder.toString();}private static String getModuleContext(String userPrincipal, String keyTabPath, Module module) {StringBuilder builder = new StringBuilder();if (IS_IBM_JDK) {builder.append(module.getName()).append(" {").append(LINE_SEPARATOR);builder.append(IBM_LOGIN_MODULE).append(LINE_SEPARATOR);builder.append("credsType=both").append(LINE_SEPARATOR);builder.append("principal=\"" + userPrincipal + "\"").append(LINE_SEPARATOR);builder.append("useKeytab=\"" + keyTabPath + "\"").append(LINE_SEPARATOR);builder.append("debug=true;").append(LINE_SEPARATOR);builder.append("};").append(LINE_SEPARATOR);} else {builder.append(module.getName()).append(" {").append(LINE_SEPARATOR);builder.append(SUN_LOGIN_MODULE).append(LINE_SEPARATOR);builder.append("useKeyTab=true").append(LINE_SEPARATOR);builder.append("keyTab=\"" + keyTabPath + "\"").append(LINE_SEPARATOR);builder.append("principal=\"" + userPrincipal + "\"").append(LINE_SEPARATOR);builder.append("useTicketCache=false").append(LINE_SEPARATOR);builder.append("storeKey=true").append(LINE_SEPARATOR);builder.append("debug=true;").append(LINE_SEPARATOR);builder.append("};").append(LINE_SEPARATOR);}return builder.toString();}public static void securityPrepare(String principal, String keyTabFilePath, String krb5ConfigPath) throws IOException {// windows路径下分隔符替换keyTabFilePath = keyTabFilePath.replace("\\", "\\\\");krb5ConfigPath = krb5ConfigPath.replace("\\", "\\\\");LoginUtil.setKrb5Config(krb5ConfigPath);LoginUtil.setZookeeperServerPrincipal("zookeeper/hadoop.hadoop.com");LoginUtil.setJaasFile(principal, keyTabFilePath);}/** 判断文件是否存在*/private static boolean isFileExists(String fileName) {File file = new File(fileName);return file.exists();}}

上文中截图的java目录下有一个entity包，该包是上文提到过的特殊处理kafka message格式所用到的一些实体类，没什么借鉴意义，就不进行展示了。

• plugin.json

该文件主要是用来定义插件的信息，方便datax加载到我们的插件。其中name与class属性需要跟实际名称及路径保持一致。

{"name": "kafkawriter","class": "com.alibaba.datax.plugin.writer.kafkawriter.KafkaWriter","description": "kafka writer","developer": "alibaba"}

• plugin_job_template.json

该文件主要定义同步任务的配置示例。

{"name": "kafkawriter","parameter": {"bootstrapServers": "11.1.1.111:9092","topic": "test-topic","ack": "all","column": ["id","name","description","weight"],"batchSize": 1000,"retries": 0,"keySerializer": "org.apache.kafka.common.serialization.StringSerializer","valueSerializer": "org.apache.kafka.common.serialization.StringSerializer","topicNumPartition": 1,"topicReplicationFactor": 1}}

上文基本将kafka writer中的相关代码都展示完毕，至此也是基本完成了kafkawriter插件的开发。打包完成之后，就可以愉快的进行测试了。