一、avro是一个数据序列化框架，可以高效得进行序列化和反序列化，支持C, C++, C#,java,php, Python, 和Ruby语言。现在使用Java来读写。
二、环境搭建
1、下载avro-1.7.7.jar and avro-tools-1.7.7.jar两个jar包，放到指定文件目录。下载地址 http://www.trieuvan.com/apache/avro/avro-1.7.7/java/
我放到了D:\soft\avro 文件夹，在改目录下新建java文件夹，用来存放生成的Java代码
2、该目录下新建user.avsc文件，内容是：
{"namespace": "example.avro","type": "record","name": "User","fields": [
{"name": "name", "type": "string"},
{"name": "favorite_number", "type": ["int", "null"]},
{"name": "favorite_color", "type": ["string", "null"]}
]
}
3、打开cmd，进入到该目录,执行命令生成User类,注意命令后面有个"."，表示生成的代码放在本目录下。
java -jar avro-tools-1.7.7.jar compile schema user.avsc java .
在该文件夹下的Java文件下的../example/avro/目录下就会生成User.java文件。
4.使用eclipse新建maven项目，在pom.xml加入avro的依赖。
<dependency>
<groupId>org.apache.avro</groupId>
<artifactId>avro</artifactId>
<version>1.7.7</version>
</dependency>
三、生成的User.java文件的内容如下。
把生成的User.java类复制到工程中，注意这个User.java里面生成的User类及其内部类的包名默认是user.avsc文件中的namespace的值，
在本例中也就是example.avro。需要全部替换为自己的包名。
最简单的方法就是把User.java中的example.avro全部替换为自己的包名。
/*** Autogenerated by Avro
*
* DO NOT EDIT DIRECTLY*/packageexample.avro;
@SupPRessWarnings("all")
@org.apache.avro.specific.AvroGeneratedpublicclassUserextendsorg.apache.avro.specific.SpecificRecordBaseimplementsorg.apache.avro.specific.SpecificRecord {publicstaticfinalorg.apache.avro.Schema SCHEMA$ =neworg.apache.avro.Schema.Parser().parse("{\"type\":\"record\",\"name\":\"User\",\"namespace\":\"example.avro\",\"fields\":[{\"name\":\"name\",\"type\":\"string\"},{\"name\":\"favorite_number\",\"type\":[\"int\",\"null\"]},{\"name\":\"favorite_color\",\"type\":[\"string\",\"null\"]}]}");publicstaticorg.apache.avro.Schema getClassSchema() {returnSCHEMA$; }
@Deprecatedpublicjava.lang.CharSequence name;
@Deprecatedpublicjava.lang.Integer favorite_number;
@Deprecatedpublicjava.lang.CharSequence favorite_color;/*** Default constructor. Note that this does not initialize fields
* to their default values from the schema. If that is desired then
* one should use <code>newBuilder()</code>.*/publicUser() {}/*** All-args constructor.*/publicUser(java.lang.CharSequence name, java.lang.Integer favorite_number, java.lang.CharSequence favorite_color) {this.name =name;this.favorite_number =favorite_number;this.favorite_color =favorite_color;
}publicorg.apache.avro.Schema getSchema() {returnSCHEMA$; }//Used by DatumWriter.applications should not call.publicjava.lang.Object get(intfield$) {switch(field$) {case0:returnname;case1:returnfavorite_number;case2:returnfavorite_color;default:throwneworg.apache.avro.AvroRuntimeException("Bad index");
}
}//Used by DatumReader. Applications should not call.@SuppressWarnings(value="unchecked")publicvoidput(intfield$, java.lang.Object value$) {switch(field$) {case0: name = (java.lang.CharSequence)value$;
break;case1: favorite_number = (java.lang.Integer)value$;
break;case2: favorite_color = (java.lang.CharSequence)value$;
break;default:throwneworg.apache.avro.AvroRuntimeException("Bad index");
}
}/*** Gets the value of the 'name' field.*/publicjava.lang.CharSequence getName() {returnname;
}/*** Sets the value of the 'name' field.
*@paramvalue the value to set.*/publicvoidsetName(java.lang.CharSequence value) {this.name =value;
}/*** Gets the value of the 'favorite_number' field.*/publicjava.lang.Integer getFavoriteNumber() {returnfavorite_number;
}/*** Sets the value of the 'favorite_number' field.
*@paramvalue the value to set.*/publicvoidsetFavoriteNumber(java.lang.Integer value) {this.favorite_number =value;
}/*** Gets the value of the 'favorite_color' field.*/publicjava.lang.CharSequence getFavoriteColor() {returnfavorite_color;
}/*** Sets the value of the 'favorite_color' field.
*@paramvalue the value to set.*/publicvoidsetFavoriteColor(java.lang.CharSequence value) {this.favorite_color =value;
}/**Creates a new User RecordBuilder*/publicstaticexample.avro.User.Builder newBuilder() {returnnewexample.avro.User.Builder();
}/**Creates a new User RecordBuilder by copying an existing Builder*/publicstaticexample.avro.User.Builder newBuilder(example.avro.User.Builder other) {returnnewexample.avro.User.Builder(other);
}/**Creates a new User RecordBuilder by copying an existing User instance*/publicstaticexample.avro.User.Builder newBuilder(example.avro.User other) {returnnewexample.avro.User.Builder(other);
}/*** RecordBuilder for User instances.*/publicstaticclassBuilderextendsorg.apache.avro.specific.SpecificRecordBuilderBase<User>implementsorg.apache.avro.data.RecordBuilder<User>{privatejava.lang.CharSequence name;privatejava.lang.Integer favorite_number;privatejava.lang.CharSequence favorite_color;/**Creates a new Builder*/privateBuilder() {super(example.avro.User.SCHEMA$);
}/**Creates a Builder by copying an existing Builder*/privateBuilder(example.avro.User.Builder other) {super(other);if(isValidValue(fields()[0], other.name)) {this.name = data().deepCopy(fields()[0].schema(), other.name);
fieldSetFlags()[0] =true;
}if(isValidValue(fields()[1], other.favorite_number)) {this.favorite_number = data().deepCopy(fields()[1].schema(), other.favorite_number);
fieldSetFlags()[1] =true;
}if(isValidValue(fields()[2], other.favorite_color)) {this.favorite_color = data().deepCopy(fields()[2].schema(), other.favorite_color);
fieldSetFlags()[2] =true;
}
}/**Creates a Builder by copying an existing User instance*/privateBuilder(example.avro.User other) {super(example.avro.User.SCHEMA$);if(isValidValue(fields()[0], other.name)) {this.name = data().deepCopy(fields()[0].schema(), other.name);
fieldSetFlags()[0] =true;
}if(isValidValue(fields()[1], other.favorite_number)) {this.favorite_number = data().deepCopy(fields()[1].schema(), other.favorite_number);
fieldSetFlags()[1] =true;
}if(isValidValue(fields()[2], other.favorite_color)) {this.favorite_color = data().deepCopy(fields()[2].schema(), other.favorite_color);
fieldSetFlags()[2] =true;
}
}/**Gets the value of the 'name' field*/publicjava.lang.CharSequence getName() {returnname;
}/**Sets the value of the 'name' field*/publicexample.avro.User.Builder setName(java.lang.CharSequence value) {
validate(fields()[0], value);this.name =value;
fieldSetFlags()[0] =true;returnthis;
}/**Checks whether the 'name' field has been set*/publicbooleanhasName() {returnfieldSetFlags()[0];
}/**Clears the value of the 'name' field*/publicexample.avro.User.Builder clearName() {
name=null;
fieldSetFlags()[0] =false;returnthis;
}/**Gets the value of the 'favorite_number' field*/publicjava.lang.Integer getFavoriteNumber() {returnfavorite_number;
}/**Sets the value of the 'favorite_number' field*/publicexample.avro.User.Builder setFavoriteNumber(java.lang.Integer value) {
validate(fields()[1], value);this.favorite_number =value;
fieldSetFlags()[1] =true;returnthis;
}/**Checks whether the 'favorite_number' field has been set*/publicbooleanhasFavoriteNumber() {returnfieldSetFlags()[1];
}/**Clears the value of the 'favorite_number' field*/publicexample.avro.User.Builder clearFavoriteNumber() {
favorite_number=null;
fieldSetFlags()[1] =false;returnthis;
}/**Gets the value of the 'favorite_color' field*/publicjava.lang.CharSequence getFavoriteColor() {returnfavorite_color;
}/**Sets the value of the 'favorite_color' field*/publicexample.avro.User.Builder setFavoriteColor(java.lang.CharSequence value) {
validate(fields()[2], value);this.favorite_color =value;
fieldSetFlags()[2] =true;returnthis;
}/**Checks whether the 'favorite_color' field has been set*/publicbooleanhasFavoriteColor() {returnfieldSetFlags()[2];
}/**Clears the value of the 'favorite_color' field*/publicexample.avro.User.Builder clearFavoriteColor() {
favorite_color=null;
fieldSetFlags()[2] =false;returnthis;
}
@OverridepublicUser build() {try{
User record=newUser();
record.name= fieldSetFlags()[0] ?this.name : (java.lang.CharSequence) defaultValue(fields()[0]);
record.favorite_number= fieldSetFlags()[1] ?this.favorite_number : (java.lang.Integer) defaultValue(fields()[1]);
record.favorite_color= fieldSetFlags()[2] ?this.favorite_color : (java.lang.CharSequence) defaultValue(fields()[2]);returnrecord;
}catch(Exception e) {throwneworg.apache.avro.AvroRuntimeException(e);
}
}
}
}
四、用Java实现序列化，即写avro文件。
新建一个Java类
public static void main(String[] args) throws IOException {
// 声明并初始化User对象
// 方式一
User user1 =newUser();
user1.setName("zhangsan");
user1.setFavoriteNumber(21);
user1.setFavoriteColor(null);
// 方式二 使用构造函数//Alternate constructorUser user2 =newUser("Ben", 7, "red");
// 方式三，使用Build方式//Construct via builderUser user3 =User.newBuilder()
.setName("Charlie")
.setFavoriteColor("blue")
.setFavoriteNumber(null)
.build();
String path = "D:\\tmp\\user.avro"; // avro文件存放目录
DatumWriter<User> userDatumWriter =newSpecificDatumWriter<User>(User.class);
DataFileWriter<User> dataFileWriter =newDataFileWriter<User>(userDatumWriter);
dataFileWriter.create(user1.getSchema(),newFile(path));
// 把生成的user对象写入到avro文件
dataFileWriter.append(user1);
dataFileWriter.append(user2);
dataFileWriter.append(user3);
dataFileWriter.close();
}
run一下代码，查看指定文件目录是否生成了avro文件。
五、Java读取avro文件，即实现avro反序列化。
publicstaticvoidmain(String[] args)throwsIOException {
DatumReader<User> reader =newSpecificDatumReader<User>(User.class);
DataFileReader<User> dataFileReader =newDataFileReader<User>(newFile("D:\\tmp\\user.avro"), reader);
User user=null;while(dataFileReader.hasNext()) {
user=dataFileReader.next();
System.out.println(user);
}
}
运行结果：
{"name": "zhangsan", "favorite_number": 21, "favorite_color":null}
{"name": "Ben", "favorite_number": 7, "favorite_color": "red"}
{"name": "Charlie", "favorite_number":null, "favorite_color": "blue"}
至此，例子写完。