java基础---->序列化框架arvo的使用

　　这里面我们介绍一下序列化框架arvo的使用，在kafka中使用的就是这个。

arvo的使用

一、需要通过插件生成Model类方式

一、生成我们的数据模型User.java

我们在resources里面定义即将要生成的User类的avsc结构。user.avsc的内容如下

{
    "namespace": "com.linux.huhx.avro",
    "type": "record",
    "name": "User",
    "fields": [
        {
            "name": "name",
            "type": "string"
        },
        {
            "name": "favorite_number",
            "type": [
                "int",
                "null"
            ]
        },
        {
            "name": "favorite_color",
            "type": [
                "string",
                "null"
            ]
        }
    ]
}

然后我们在pom.xml添加依赖与avro-maven-plugin插件

<dependency>
    <groupId>org.apache.avro</groupId>
    <artifactId>avro</artifactId>
    <version>1.8.2</version>
</dependency>

<!-- add arvo plugin -->
<plugin>
    <groupId>org.apache.avro</groupId>
    <artifactId>avro-maven-plugin</artifactId>
    <version>1.8.2</version>
    <executions>
        <execution>
            <phase>generate-sources</phase>
            <goals>
                <goal>schema</goal>
            </goals>
            <configuration>
                <sourceDirectory>${project.basedir}/src/main/resources</sourceDirectory>
                <outputDirectory>${project.basedir}/src/main/java</outputDirectory>
            </configuration>
        </execution>
    </executions>
</plugin>

运行mvn generate-sources，就可以在arvo目录下面看到生成的User类。内容如下：

/**
 * Autogenerated by Avro
 *
 * DO NOT EDIT DIRECTLY
 */
package com.linux.huhx.avro;

import org.apache.avro.specific.SpecificData;
import org.apache.avro.message.BinaryMessageEncoder;
import org.apache.avro.message.BinaryMessageDecoder;
import org.apache.avro.message.SchemaStore;

@SuppressWarnings("all")
@org.apache.avro.specific.AvroGenerated
public class User extends org.apache.avro.specific.SpecificRecordBase implements org.apache.avro.specific.SpecificRecord {
  private static final long serialVersionUID = -1677175913369996238L;
  public static final org.apache.avro.Schema SCHEMA$ = new org.apache.avro.Schema.Parser().parse("{"type":"record","name":"User","namespace":"com.linux.huhx.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$; }

  private static SpecificData MODEL$ = new SpecificData();

  private static final BinaryMessageEncoder<User> ENCODER =
      new BinaryMessageEncoder<User>(MODEL$, SCHEMA$);

  private static final BinaryMessageDecoder<User> DECODER =
      new BinaryMessageDecoder<User>(MODEL$, SCHEMA$);

  /**
   * Return the BinaryMessageDecoder instance used by this class.
   */
  public static BinaryMessageDecoder<User> getDecoder() {
    return DECODER;
  }

  /**
   * Create a new BinaryMessageDecoder instance for this class that uses the specified {@link SchemaStore}.
   * @param resolver a {@link SchemaStore} used to find schemas by fingerprint
   */
  public static BinaryMessageDecoder<User> createDecoder(SchemaStore resolver) {
    return new BinaryMessageDecoder<User>(MODEL$, SCHEMA$, resolver);
  }

  /** Serializes this User to a ByteBuffer. */
  public java.nio.ByteBuffer toByteBuffer() throws java.io.IOException {
    return ENCODER.encode(this);
  }

  /** Deserializes a User from a ByteBuffer. */
  public static User fromByteBuffer(
      java.nio.ByteBuffer b) throws java.io.IOException {
    return DECODER.decode(b);
  }

  @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 <code>newBuilder()</code>.
   */
  public User() {}

  /**
   * All-args constructor.
   * @param name The new value for name
   * @param favorite_number The new value for favorite_number
   * @param favorite_color The new value for favorite_color
   */
  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.
   * @return 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.
   * @return 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.
   * @return 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.
   * @return A new User RecordBuilder
   */
  public static com.linux.huhx.avro.User.Builder newBuilder() {
    return new com.linux.huhx.avro.User.Builder();
  }

  /**
   * Creates a new User RecordBuilder by copying an existing Builder.
   * @param other The existing builder to copy.
   * @return A new User RecordBuilder
   */
  public static com.linux.huhx.avro.User.Builder newBuilder(com.linux.huhx.avro.User.Builder other) {
    return new com.linux.huhx.avro.User.Builder(other);
  }

  /**
   * Creates a new User RecordBuilder by copying an existing User instance.
   * @param other The existing instance to copy.
   * @return A new User RecordBuilder
   */
  public static com.linux.huhx.avro.User.Builder newBuilder(com.linux.huhx.avro.User other) {
    return new com.linux.huhx.avro.User.Builder(other);
  }

  /**
   * RecordBuilder for User instances.
   */
  public static class Builder extends org.apache.avro.specific.SpecificRecordBuilderBase<User>
    implements org.apache.avro.data.RecordBuilder<User> {

    private java.lang.CharSequence name;
    private java.lang.Integer favorite_number;
    private java.lang.CharSequence favorite_color;

    /** Creates a new Builder */
    private Builder() {
      super(SCHEMA$);
    }

    /**
     * Creates a Builder by copying an existing Builder.
     * @param other The existing Builder to copy.
     */
    private Builder(com.linux.huhx.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
     * @param other The existing instance to copy.
     */
    private Builder(com.linux.huhx.avro.User other) {
            super(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.
      * @return The value.
      */
    public java.lang.CharSequence getName() {
      return name;
    }

    /**
      * Sets the value of the 'name' field.
      * @param value The value of 'name'.
      * @return This builder.
      */
    public com.linux.huhx.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.
      * @return True if the 'name' field has been set, false otherwise.
      */
    public boolean hasName() {
      return fieldSetFlags()[0];
    }


    /**
      * Clears the value of the 'name' field.
      * @return This builder.
      */
    public com.linux.huhx.avro.User.Builder clearName() {
      name = null;
      fieldSetFlags()[0] = false;
      return this;
    }

    /**
      * Gets the value of the 'favorite_number' field.
      * @return The value.
      */
    public java.lang.Integer getFavoriteNumber() {
      return favorite_number;
    }

    /**
      * Sets the value of the 'favorite_number' field.
      * @param value The value of 'favorite_number'.
      * @return This builder.
      */
    public com.linux.huhx.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.
      * @return True if the 'favorite_number' field has been set, false otherwise.
      */
    public boolean hasFavoriteNumber() {
      return fieldSetFlags()[1];
    }


    /**
      * Clears the value of the 'favorite_number' field.
      * @return This builder.
      */
    public com.linux.huhx.avro.User.Builder clearFavoriteNumber() {
      favorite_number = null;
      fieldSetFlags()[1] = false;
      return this;
    }

    /**
      * Gets the value of the 'favorite_color' field.
      * @return The value.
      */
    public java.lang.CharSequence getFavoriteColor() {
      return favorite_color;
    }

    /**
      * Sets the value of the 'favorite_color' field.
      * @param value The value of 'favorite_color'.
      * @return This builder.
      */
    public com.linux.huhx.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.
      * @return True if the 'favorite_color' field has been set, false otherwise.
      */
    public boolean hasFavoriteColor() {
      return fieldSetFlags()[2];
    }


    /**
      * Clears the value of the 'favorite_color' field.
      * @return This builder.
      */
    public com.linux.huhx.avro.User.Builder clearFavoriteColor() {
      favorite_color = null;
      fieldSetFlags()[2] = false;
      return this;
    }

    @Override
    @SuppressWarnings("unchecked")
    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 (java.lang.Exception e) {
        throw new org.apache.avro.AvroRuntimeException(e);
      }
    }
  }

  @SuppressWarnings("unchecked")
  private static final org.apache.avro.io.DatumWriter<User>
    WRITER$ = (org.apache.avro.io.DatumWriter<User>)MODEL$.createDatumWriter(SCHEMA$);

  @Override public void writeExternal(java.io.ObjectOutput out)
    throws java.io.IOException {
    WRITER$.write(this, SpecificData.getEncoder(out));
  }

  @SuppressWarnings("unchecked")
  private static final org.apache.avro.io.DatumReader<User>
    READER$ = (org.apache.avro.io.DatumReader<User>)MODEL$.createDatumReader(SCHEMA$);

  @Override public void readExternal(java.io.ObjectInput in)
    throws java.io.IOException {
    READER$.read(this, SpecificData.getDecoder(in));
  }

}

二、序列化我们的User类

public static void serializing() throws IOException {
    User user1 = new User();
    user1.setName("Alyssa");
    user1.setFavoriteNumber(256);

    User user2 = new User("Ben", 7, "red");

    User user3 = User.newBuilder()
            .setName("Charlie")
            .setFavoriteColor("blue")
            .setFavoriteNumber(null)
            .build();

    DatumWriter<User> userDatumWriter = new SpecificDatumWriter<>(User.class);
    DataFileWriter<User> dataFileWriter = new DataFileWriter<>(userDatumWriter);
    dataFileWriter.create(user1.getSchema(), new File("file/users.avro"));

    dataFileWriter.append(user1);
    dataFileWriter.append(user2);
    dataFileWriter.append(user3);
    dataFileWriter.close();
}

上面可以看到多种的创建User类的方式，运行上述代码会把User的有一个实例序列化到文件file/users.avro中。

三、反序列化我们的User类

public static void deserializing() throws IOException {
    // Deserialize Users from disk
    DatumReader<User> userDatumReader = new SpecificDatumReader<>(User.class);
    DataFileReader<User> dataFileReader = new DataFileReader<User>(new File("file/users.avro"), userDatumReader);
    User user = null;
    while (dataFileReader.hasNext()) {
        user = dataFileReader.next(user);
        System.out.println(user);
    }
}

根据我们上述生成的序列化file/users.avro文件反序列化生成的User实例，可以看到如下的输出：

{"name": "Alyssa", "favorite_number": 256, "favorite_color": null}
{"name": "Ben", "favorite_number": 7, "favorite_color": "red"}
{"name": "Charlie", "favorite_number": null, "favorite_color": "blue"}

二、不需要生成User类的方式

Avro中的数据始终与其相应的模式一起存储，这意味着无论我们是否提前知道模式，我们总是可以读取序列化项目。这允许我们在不生成代码的情况下执行序列化和反序列化。如果是这种方式的话，pom.xml里面的arvo插件不是必须的。

一、序列化User类

public static void serializing() throws IOException {
    Schema schema = new Schema.Parser().parse(WithoutUserGen.class.getResourceAsStream("/user.avsc"));
    GenericRecord user1 = new GenericData.Record(schema);
    user1.put("name", "Alyssa");
    user1.put("favorite_number", 256);
    // Leave favorite color null

    GenericRecord user2 = new GenericData.Record(schema);
    user2.put("name", "Ben");
    user2.put("favorite_number", 7);
    user2.put("favorite_color", "red");

    File file = new File("file/users2.avro");
    DatumWriter<GenericRecord> datumWriter = new GenericDatumWriter<>(schema);
    DataFileWriter<GenericRecord> dataFileWriter = new DataFileWriter<>(datumWriter);
    dataFileWriter.create(schema, file);
    dataFileWriter.append(user1);
    dataFileWriter.append(user2);
    dataFileWriter.close();
}

这里把两个User类的实例序列化到file/users2.avro文件中

二、反序列化User类

public static void deserializing() throws IOException {
    Schema schema = new Schema.Parser().parse(WithoutUserGen.class.getResourceAsStream("/user.avsc"));
    File file = new File("file/users2.avro");
    DatumReader<GenericRecord> datumReader = new GenericDatumReader<>(schema);
    DataFileReader<GenericRecord> dataFileReader = new DataFileReader<>(file, datumReader);
    GenericRecord user = null;
    while (dataFileReader.hasNext()) {
        user = dataFileReader.next(user);
        System.out.println(user);
    }
}

可以看到以下的输出

{"name": "Alyssa", "favorite_number": 256, "favorite_color": null}
{"name": "Ben", "favorite_number": 7, "favorite_color": "red"}

友情链接