maven依赖avro_【Avro一】Avro入门

本文的目的主要是总结下基于Avro Schema代码生成，然后进行序列化和反序列化开发的基本流程。需要指出的是，Avro并不要求一定得根据Schema文件生成代码，这对于动态类型语言很有用。

1. 添加Maven依赖

xmlns:xsi=”http://www.w3.org/2001/XMLSchema-instance”

xsi:schemaLocation=”http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd”>

4.0.0

learn

learn.avro

1.0-SNAPSHOT

org.apache.avro

avro

1.7.7

org.apache.avro

avro-maven-plugin

1.7.7

generate-sources

schema

protocol

idl-protocol

${project.basedir}/src/main/avro/

${project.basedir}/src/main/java/

org.apache.maven.plugins

maven-compiler-plugin

1.7

1.7

2.定义schema文件(users.avsc)

放置到src/main/avro目录下

{“namespace”: “examples.avro.simple”,

“type”: “record”,

“name”: “User”,

“fields”: [

{“name”: “name”, “type”: “string”},

{“name”: “favorite_number”, “type”: [“int”, “null”]},

{“name”: “favorite_color”, “type”: [“string”, “null”]}

]

}

namespace:包名

type: record表示记录，可以理解为几个field构成的一个record，类似于Java的JavaBean

name:类名

fiels:成员变量，favorite_number最后会解释成getFavoriteNumber和setFavoriteNumber

3. 生成User类

在Intellij Idea的Maven视图中,learn avro->Plugins->avro->avro:schema,右击avro:schema，执行Run Maven Build，生成schema对应的Java实体类

/**

* Autogenerated by Avro

*

* DO NOT EDIT DIRECTLY

*/

package examples.avro.simple;

@SuppressWarnings(“all”)

@org.apache.avro.specific.AvroGenerated

public class User extends org.apache.avro.specific.SpecificRecordBase implements org.apache.avro.specific.SpecificRecord {

public static final org.apache.avro.Schema SCHEMA$ = new org.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\”]}]}”);

public static org.apache.avro.Schema getClassSchema() { return SCHEMA$; }

@Deprecated public java.lang.CharSequence name;

@Deprecated public java.lang.Integer favorite_number;

@Deprecated public java.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 newBuilder().

*/

public User() {}

/**

* All-args constructor.

*/

public User(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;

}

public org.apache.avro.Schema getSchema() { return SCHEMA$; }

// Used by DatumWriter. Applications should not call.

public java.lang.Object get(int field$) {

switch (field$) {

case 0: return name;

case 1: return favorite_number;

case 2: return favorite_color;

default: throw new org.apache.avro.AvroRuntimeException(“Bad index”);

}

}

// Used by DatumReader. Applications should not call.

@SuppressWarnings(value=”unchecked”)

public void put(int field$, java.lang.Object value$) {

switch (field$) {

case 0: name = (java.lang.CharSequence)value$; break;

case 1: favorite_number = (java.lang.Integer)value$; break;

case 2: favorite_color = (java.lang.CharSequence)value$; break;

default: throw new org.apache.avro.AvroRuntimeException(“Bad index”);

}

}

/**

* Gets the value of the ‘name’ field.

*/

public java.lang.CharSequence getName() {

return name;

}

/**

* Sets the value of the ‘name’ field.

* @param value the value to set.

*/

public void setName(java.lang.CharSequence value) {

this.name = value;

}

/**

* Gets the value of the ‘favorite_number’ field.

*/

public java.lang.Integer getFavoriteNumber() {

return favorite_number;

}

/**

* Sets the value of the ‘favorite_number’ field.

* @param value the value to set.

*/

public void setFavoriteNumber(java.lang.Integer value) {

this.favorite_number = value;

}

/**

* Gets the value of the ‘favorite_color’ field.

*/

public java.lang.CharSequence getFavoriteColor() {

return favorite_color;

}

/**

* Sets the value of the ‘favorite_color’ field.

* @param value the value to set.

*/

public void setFavoriteColor(java.lang.CharSequence value) {

this.favorite_color = value;

}

/** Creates a new User RecordBuilder */

public static User.Builder newBuilder() {

return new User.Builder();

}

/** Creates a new User RecordBuilder by copying an existing Builder */

public static User.Builder newBuilder(User.Builder other) {

return new User.Builder(other);

}

/** Creates a new User RecordBuilder by copying an existing User instance */

public static User.Builder newBuilder(User other) {

return new User.Builder(other);

}

/**

* RecordBuilder for User instances.

*/

public static class Builder extends org.apache.avro.specific.SpecificRecordBuilderBase

implements org.apache.avro.data.RecordBuilder {

private java.lang.CharSequence name;

private java.lang.Integer favorite_number;

private java.lang.CharSequence favorite_color;

/** Creates a new Builder */

private Builder() {

super(User.SCHEMA$);

}

/** Creates a Builder by copying an existing Builder */

private Builder(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 */

private Builder(User other) {

super(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 */

public java.lang.CharSequence getName() {

return name;

}

/** Sets the value of the ‘name’ field */

public User.Builder setName(java.lang.CharSequence value) {

validate(fields()[0], value);

this.name = value;

fieldSetFlags()[0] = true;

return this;

}

/** Checks whether the ‘name’ field has been set */

public boolean hasName() {

return fieldSetFlags()[0];

}

/** Clears the value of the ‘name’ field */

public User.Builder clearName() {

name = null;

fieldSetFlags()[0] = false;

return this;

}

/** Gets the value of the ‘favorite_number’ field */

public java.lang.Integer getFavoriteNumber() {

return favorite_number;

}

/** Sets the value of the ‘favorite_number’ field */

public User.Builder setFavoriteNumber(java.lang.Integer value) {

validate(fields()[1], value);

this.favorite_number = value;

fieldSetFlags()[1] = true;

return this;

}

/** Checks whether the ‘favorite_number’ field has been set */

public boolean hasFavoriteNumber() {

return fieldSetFlags()[1];

}

/** Clears the value of the ‘favorite_number’ field */

public User.Builder clearFavoriteNumber() {

favorite_number = null;

fieldSetFlags()[1] = false;

return this;

}

/** Gets the value of the ‘favorite_color’ field */

public java.lang.CharSequence getFavoriteColor() {

return favorite_color;

}

/** Sets the value of the ‘favorite_color’ field */

public User.Builder setFavoriteColor(java.lang.CharSequence value) {

validate(fields()[2], value);

this.favorite_color = value;

fieldSetFlags()[2] = true;

return this;

}

/** Checks whether the ‘favorite_color’ field has been set */

public boolean hasFavoriteColor() {

return fieldSetFlags()[2];

}

/** Clears the value of the ‘favorite_color’ field */

public User.Builder clearFavoriteColor() {

favorite_color = null;

fieldSetFlags()[2] = false;

return this;

}

@Override

public User build() {

try {

User record = new User();

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]);

return record;

} catch (Exception e) {

throw new org.apache.avro.AvroRuntimeException(e);

}

}

}

}

4. User类序列化和反序列化测试

package examples.avro.simple;

import java.io.File;

import java.io.Serializable;

import org.apache.avro.file.DataFileReader;

import org.apache.avro.file.DataFileWriter;

import org.apache.avro.io.DatumReader;

import org.apache.avro.io.DatumWriter;

import org.apache.avro.specific.SpecificDatumReader;

import org.apache.avro.specific.SpecificDatumWriter;

public class UserTest {

public static void main(String[] args) throws Exception {

///无参构造函数，依赖设值注入

User user1 = new User();

user1.setName(“Alyssa”);

user1.setFavoriteNumber(256);

//user1没有对favorite color赋值

///注意：User并没有实现Java的Serializable接口

System.out.println(user1 instanceof Serializable);

///重载的构造方法

User user2 = new User(“Ben”, 7, “red”);

//使用builder构建对象

User user3 = User.newBuilder()

.setName(“Charlie”)

.setFavoriteColor(“blue”)

.setFavoriteNumber(null)

.build();

System.out.println(user3.getName() + “,” + user3.getFavoriteColor());

///1. 序列化包含Schema和3个User对象到c:/users.avro文件

DatumWriter userDatumWriter = new SpecificDatumWriter(User.class);

DataFileWriter dataFileWriter = new DataFileWriter(userDatumWriter);

dataFileWriter.create(user1.getSchema(), new File(“c:/users.avro”));

dataFileWriter.append(user1);

dataFileWriter.append(user2);

dataFileWriter.append(user3);

dataFileWriter.close();

///2. 从c:/users.avro文件反序列化对象

DatumReader userDatumReader = new SpecificDatumReader(User.class);

DataFileReader dataFileReader = new DataFileReader(new File(“c:/users.avro”), userDatumReader);

User user = null;

while (dataFileReader.hasNext()) {

// Reuse user object by passing it to next(). This saves us from

// allocating and garbage collecting many objects for files with

// many items.

user = dataFileReader.next(user);

System.out.println(user); ///输出JSON格式的数据，Avro对User类的toString进行了改写

}

}

}