转载出处 http://www.cnblogs.com/fillPv/p/5009737.html
Java读写avro例子
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。
org.apache.avro avro 1.7.7
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 */package example.avro;
@SuppressWarnings("all")
@org.apache.avro.specific.AvroGeneratedpublic 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 example.avro.User.Builder newBuilder() { return new example.avro.User.Builder();
}
/** Creates a new User RecordBuilder by copying an existing Builder */
public static example.avro.User.Builder newBuilder(example.avro.User.Builder other) { return new example.avro.User.Builder(other);
}
/** Creates a new User RecordBuilder by copying an existing User instance */
public static example.avro.User.Builder newBuilder(example.avro.User other) { return new example.avro.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(example.avro.User.SCHEMA$);
}
/** Creates a Builder by copying an existing Builder */
private Builder(example.avro.User.Builder other) { super(other); if (isValidValue(fields()[0], other.name)) { this.name = data().deepCopy(fields()[0].schema(), other.name);
fieldSetFlags()[0] = true;
} if (isValidValue(fields()[1], other.favorite_number)) { this.favorite_number = data().deepCopy(fields()[1].schema(), other.favorite_number);
fieldSetFlags()[1] = true;
} if (isValidValue(fields()[2], other.favorite_color)) { this.favorite_color = data().deepCopy(fields()[2].schema(), other.favorite_color);
fieldSetFlags()[2] = true;
}
}
/** Creates a Builder by copying an existing User instance */
private Builder(example.avro.User other) { super(example.avro.User.SCHEMA$); 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 */
public java.lang.CharSequence getName() { return name;
}
/** Sets the value of the 'name' field */
public example.avro.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 example.avro.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 example.avro.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 example.avro.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 example.avro.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 example.avro.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);
}
}
}
}
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 = "zhangsan"21
User user2 = User("Ben", 7, "red"
User user3 ="Charlie""blue" userDatumWriter = SpecificDatumWriter(User. dataFileWriter = DataFileWriter File(path
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。
public static void main(String[] args) throws IOException {
DatumReader reader = new SpecificDatumReader(User.class);
DataFileReader dataFileReader = new DataFileReader(new File("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。