Thrift compiler代码生成类解析

代码生成类解析：

Thrift--facebook RPC框架，介绍就不说了，百度，google一大把，使用也不介绍，直接上结构和分析吧。

Hello.thrift文件内容如下：

namespace java com.tomsun.thrift.generated.demo
service Hello {
   string helloString(1:string para)
   }

内容很简单，申明个RPC service(Hello),服务方法helloString,方法参数格式（seq: parameter type, parameter name），参数需要标号（1: xxx xxx, 2: xxx xxx）, namespace 指定生成代码语言类型（java）,和Java包名（本文只讨论java ^#^!）.

类文件解析：

话说就上面定义一个service(只包含一个method),可生成的类文件可是一个庞然大物(975行代码)，在此就不全贴出来了，说明时会贴出关键代码用于说明。

因为thrift是一个完整的RPC框架，内部结构分的很细，所以代码生成量理所当然，（protobuf的所谓的RPC，只不过是个架子，空的，基本上都得自己去实现。当protobuf序列化自己感觉比thrift丰富多了（sint,fint,int,uint））,

但thrift支持的容器类型（List，set, map）比protobuf多（list）,具体介绍等以后再详细，回到正题。

thrift compiler生成的Hello.java 文件，以服务名为类文件名。服务接口定义如下：

   public interface Iface { //同步RPC服务调用接口定义

     public String helloString(String para) throws org.apache.thrift.TException;

   }

   public interface AsyncIface { //异步RPC服务调用接口定义（仔细瞅，方法返回值参数string没了，方法参数多了个AsyncMethodCallback）

     public void helloString(String para, org.apache.thrift.async.AsyncMethodCallback resultHandler) throws org.apache.thrift.TException;

   }

Async形式具体返回值是通过callback回调来获得。定义如下：

 public interface AsyncMethodCallback<T> {
   /**
    * This method will be called when the remote side has completed invoking
    * your method call and the result is fully read. For oneway method calls,
    * this method will be called as soon as we have completed writing out the
    * request.
    * @param response
    */
   public void onComplete(T response);

   /**
    * This method will be called when there is an unexpected clientside
    * exception. This does not include application-defined exceptions that
    * appear in the IDL, but rather things like IOExceptions.
    * @param exception
    */
   public void onError(Exception exception);
 }

自己定义异步RPC得实现该接口，同步RPC客户端骨架及其工厂类如下。

   public static class Client extends org.apache.thrift.TServiceClient implements Iface {
     public static class Factory implements org.apache.thrift.TServiceClientFactory<Client> {

Client，客户端调用RPC骨架实现，封装了底层复杂RPC序列化，和网络传输。

 public static class AsyncClient extends org.apache.thrift.async.TAsyncClient implements AsyncIface {
    public static class Factory implements org.apache.thrift.async.TAsyncClientFactory<AsyncClient> {

感觉thrift的工厂有点鸡肋的感念，没有设计模式三种工厂那种封装的味道，可有可无。

具体看一下同步骨架内部：

   public String helloString(String para) throws org.apache.thrift.TException
     {
       send_helloString(para);
       return recv_helloString();
     }

     public void send_helloString(String para) throws org.apache.thrift.TException
     {
       helloString_args args = new helloString_args();
       args.setPara(para);
       sendBase("helloString", args);
     }

     public String recv_helloString() throws org.apache.thrift.TException
     {
       helloString_result result = new helloString_result();
       receiveBase(result, "helloString");
       if (result.isSetSuccess()) {
         return result.success;
       }
       throw new org.apache.thrift.TApplicationException(org.apache.thrift.TApplicationException.MISSING_RESULT, "helloString failed: unknown result");
     }

String helloString(String para)方法包含send，recv两同步操作，另外thrift为方法参数和返回值都生成一个java类，本例中的helloString_args,helloString_result.

public static class helloString_args implements org.apache.thrift.TBase<helloString_args, helloString_args._Fields>, java.io.Serializable, Cloneable, Comparable<helloString_args>

public static class helloString_result implements org.apache.thrift.TBase<helloString_result, helloString_result._Fields>, java.io.Serializable, Cloneable, Comparable<helloString_result> 

两者为rpc客户端和服务器端传输的数据，都实现TBase接口，

public interface TBase<T extends TBase<T,F>, F extends TFieldIdEnum> extends Comparable<T>,  Serializable {

  /**
   * Reads the TObject from the given input protocol.
   *
   * @param iprot Input protocol
   */
  public void read(TProtocol iprot) throws TException;

  /**
   * Writes the objects out to the protocol
   *
   * @param oprot Output protocol
   */
  public void write(TProtocol oprot) throws TException;

  /**
   * Get the F instance that corresponds to fieldId.
   */
  public F fieldForId(int fieldId);

  /**
   * Check if a field is currently set or unset.
   *
   * @param field
   */
  public boolean isSet(F field);

  /**
   * Get a field's value by field variable. Primitive types will be wrapped in
   * the appropriate "boxed" types.
   *
   * @param field
   */
  public Object getFieldValue(F field);

  /**
   * Set a field's value by field variable. Primitive types must be "boxed" in
   * the appropriate object wrapper type.
   *
   * @param field
   */
  public void setFieldValue(F field, Object value);

  public TBase<T, F> deepCopy();

  /**
   * Return to the state of having just been initialized, as though you had just
   * called the default constructor.
   */
  public void clear();
}

TBase定义read，write和具体字段是否设值的判定方法，以helloString_args具体解析：

 private static final org.apache.thrift.protocol.TStruct STRUCT_DESC = new org.apache.thrift.protocol.TStruct("helloString_args");

 private static final org.apache.thrift.protocol.TField PARA_FIELD_DESC = new org.apache.thrift.protocol.TField("para", org.apache.thrift.protocol.TType.STRING, (short)1);

struct_desc（TStruct）为thrift内部对象结构，作为远程传输读写的参数metadata元数据和标志位（readStructBegin(), writeStructEnd()）

/**
 * Helper class that encapsulates struct metadata.
 *
 */
public final class TStruct {
  public TStruct() {
    this("");
  }

  public TStruct(String n) {
    name = n;
  }

  public final String name; //（本例中为hellosString_args）
}

para_field_desc(TField)为传输结构对象中的变量结构，read,write时会对应相应的标志位（readTFiledBegin(), writeTFieldEnd()），具体为方法参数和返回值，本例中为helloString方法参数（如果多个方法参数，helloString_args中将对应多个TField元数据）：

/**
 * Helper class that encapsulates field metadata.
 *
 */
public class TField {
  public TField() {
    this("", TType.STOP, (short)0);
  }

  public TField(String n, byte t, short i) {
    name = n; //参数名
    type = t;//thrift内部类型
    id = i;// seq number,即为hello.thrift方法参数定义的num.
  }

  public final String name;
  public final byte   type;
  public final short  id;

  public String toString() {
    return "<TField name:'" + name + "' type:" + type + " field-id:" + id + ">";
  }

  @Override
  public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + id;
    result = prime * result + ((name == null) ? 0 : name.hashCode());
    result = prime * result + type;
    return result;
  }

  @Override
  public boolean equals(Object obj) {
    if (this == obj)
      return true;
    if (obj == null)
      return false;
    if (getClass() != obj.getClass())
      return false;
    TField otherField = (TField) obj;
    return type == otherField.type && id == otherField.id;
  }
}

thrift内部类型：

/**
 * Type constants in the Thrift protocol.
 */
public final class TType {
  public static final byte STOP   = 0; //参数值没有设定，指定stop,read wire stream时会直接skip。
  public static final byte VOID   = 1;
  public static final byte BOOL   = 2;
  public static final byte BYTE   = 3;
  public static final byte DOUBLE = 4;
  public static final byte I16    = 6;
  public static final byte I32    = 8;
  public static final byte I64    = 10;
  public static final byte STRING = 11;
  public static final byte STRUCT = 12;
  public static final byte MAP    = 13;
  public static final byte SET    = 14;
  public static final byte LIST   = 15;
  public static final byte ENUM   = 16;
}

 static {
      schemes.put(StandardScheme.class, new helloString_argsStandardSchemeFactory());
      schemes.put(TupleScheme.class, new helloString_argsTupleSchemeFactory());
    }

注册具体stream read,write的类和对应的工厂类，两种读写方法：

 public void read(org.apache.thrift.protocol.TProtocol iprot) throws org.apache.thrift.TException {
      schemes.get(iprot.getScheme()).getScheme().read(iprot, this);
    }

    public void write(org.apache.thrift.protocol.TProtocol oprot) throws org.apache.thrift.TException {
      schemes.get(oprot.getScheme()).getScheme().write(oprot, this);
    }

 private static class helloString_argsStandardScheme extends StandardScheme<helloString_args> {

      public void read(org.apache.thrift.protocol.TProtocol iprot, helloString_args struct) throws org.apache.thrift.TException {
        org.apache.thrift.protocol.TField schemeField;
        iprot.readStructBegin();
        while (true)
        {
          schemeField = iprot.readFieldBegin();
          if (schemeField.type == org.apache.thrift.protocol.TType.STOP) {
            break;
          }
          switch (schemeField.id) {
            case 1: // PARA
              if (schemeField.type == org.apache.thrift.protocol.TType.STRING) {
                struct.para = iprot.readString();
                struct.setParaIsSet(true);
              } else {
                org.apache.thrift.protocol.TProtocolUtil.skip(iprot, schemeField.type);
              }
              break;
            default:
              org.apache.thrift.protocol.TProtocolUtil.skip(iprot, schemeField.type);
          }
          iprot.readFieldEnd();
        }
        iprot.readStructEnd();

        // check for required fields of primitive type, which can't be checked in the validate method
        struct.validate();
      }

      public void write(org.apache.thrift.protocol.TProtocol oprot, helloString_args struct) throws org.apache.thrift.TException {
        struct.validate();

        oprot.writeStructBegin(STRUCT_DESC);
        if (struct.para != null) {
          oprot.writeFieldBegin(PARA_FIELD_DESC);
          oprot.writeString(struct.para);
          oprot.writeFieldEnd();
        }
        oprot.writeFieldStop();
        oprot.writeStructEnd();
      }

    }

 private static class helloString_argsTupleScheme extends TupleScheme<helloString_args> {

      @Override
      public void write(org.apache.thrift.protocol.TProtocol prot, helloString_args struct) throws org.apache.thrift.TException {
        TTupleProtocol oprot = (TTupleProtocol) prot;
        BitSet optionals = new BitSet();
        if (struct.isSetPara()) {
          optionals.set(0);
        }
        oprot.writeBitSet(optionals, 1);
        if (struct.isSetPara()) {
          oprot.writeString(struct.para);
        }
      }

      @Override
      public void read(org.apache.thrift.protocol.TProtocol prot, helloString_args struct) throws org.apache.thrift.TException {
        TTupleProtocol iprot = (TTupleProtocol) prot;
        BitSet incoming = iprot.readBitSet(1);
        if (incoming.get(0)) {
          struct.para = iprot.readString();
          struct.setParaIsSet(true);
        }
      }
    }

  }

standard schema读写更倾向于结构化，(structBeging->fieldBegin()->value()->fieldEnd()->structEnd()),而tuple schema通过一个bitset(bit位操作)来代替（structBegin,fieldBegin,structEnd,filedEnd哪些占用流空间，因为上面提及struct,field里面包含struct名，field名，类型，seq num等占用流空间信息），减少序列化和网络传输的流大小。

public String para; // required

para,helloString_args结构内部成员（方法参数具体值）。 _Field，struct内部所有成员的enum表示，用于上面standard schema读取（见上述代码）

/** The set of fields this struct contains, along with convenience methods for finding and manipulating them. */
    public enum _Fields implements org.apache.thrift.TFieldIdEnum {
      PARA((short)1, "para");

      private static final Map<String, _Fields> byName = new HashMap<String, _Fields>();

      static {
        for (_Fields field : EnumSet.allOf(_Fields.class)) {
          byName.put(field.getFieldName(), field);
        }
      }

      /**
       * Find the _Fields constant that matches fieldId, or null if its not found.
       */
      public static _Fields findByThriftId(int fieldId) {
        switch(fieldId) {
          case 1: // PARA
            return PARA;
          default:
            return null;
        }
      }

      /**
       * Find the _Fields constant that matches fieldId, throwing an exception
       * if it is not found.
       */
      public static _Fields findByThriftIdOrThrow(int fieldId) {
        _Fields fields = findByThriftId(fieldId);
        if (fields == null) throw new IllegalArgumentException("Field " + fieldId + " doesn't exist!");
        return fields;
      }

      /**
       * Find the _Fields constant that matches name, or null if its not found.
       */
      public static _Fields findByName(String name) {
        return byName.get(name);
      }

      private final short _thriftId;
      private final String _fieldName;

      _Fields(short thriftId, String fieldName) {
        _thriftId = thriftId;
        _fieldName = fieldName;
      }

      public short getThriftFieldId() {
        return _thriftId;
      }

      public String getFieldName() {
        return _fieldName;
      }
    }

struct中field元数据metadata,FieldMetaData包含(_Field enum, fieldvaluemetadata(参数名，requirement type, TType)):

 // isset id assignments
    public static final Map<_Fields, org.apache.thrift.meta_data.FieldMetaData> metaDataMap;
    static {
      Map<_Fields, org.apache.thrift.meta_data.FieldMetaData> tmpMap = new EnumMap<_Fields, org.apache.thrift.meta_data.FieldMetaData>(_Fields.class);
      tmpMap.put(_Fields.PARA, new org.apache.thrift.meta_data.FieldMetaData("para", org.apache.thrift.TFieldRequirementType.DEFAULT,
          new org.apache.thrift.meta_data.FieldValueMetaData(org.apache.thrift.protocol.TType.STRING)));
      metaDataMap = Collections.unmodifiableMap(tmpMap);
      org.apache.thrift.meta_data.FieldMetaData.addStructMetaDataMap(helloString_args.class, metaDataMap);
    }

Requirement Type enum:

/**
 * Requirement type constants.
 *
 */
public final class TFieldRequirementType {
  public static final byte REQUIRED  = 1;
  public static final byte OPTIONAL = 2;
  public static final byte DEFAULT = 3;
}

一些设值，判断是否设值操作：

    public String getPara() {
      return this.para;
    }

    public helloString_args setPara(String para) {
      this.para = para;
      return this;
    }

    public void unsetPara() {
      this.para = null;
    }

    /** Returns true if field para is set (has been assigned a value) and false otherwise */
    public boolean isSetPara() {
      return this.para != null;
    }

<**************************************************************************************************************************************************>

服务器端同步处理器类：

public static class Processor<I extends Iface> extends org.apache.thrift.TBaseProcessor<I> implements org.apache.thrift.TProcessor 

注册实际的处理函数类：

 private static <I extends Iface> Map<String,  org.apache.thrift.ProcessFunction<I, ? extends  org.apache.thrift.TBase>> getProcessMap(Map<String,  org.apache.thrift.ProcessFunction<I, ? extends  org.apache.thrift.TBase>> processMap) {
      processMap.put("helloString", new helloString());
      return processMap;
    }

处理函数类：

 public static class helloString<I extends Iface> extends org.apache.thrift.ProcessFunction<I, helloString_args> {
      public helloString() {
        super("helloString");
      }

      public helloString_args getEmptyArgsInstance() {
        return new helloString_args();
      }

      protected boolean isOneway() {//是否是单向RPC，只调用不要求返回
        return false;
      }

      public helloString_result getResult(I iface, helloString_args args) throws org.apache.thrift.TException {
        helloString_result result = new helloString_result();
        result.success = iface.helloString(args.para);//调用用户编写的server实现类方法
        return result; //方法值类（helloString_result类）
      }
    }

  }

<**********************************************************************************************************************************************************>

Async异步client和processor有所不同，来看看AsyncClient内部：

 public AsyncClient(org.apache.thrift.protocol.TProtocolFactory protocolFactory, org.apache.thrift.async.TAsyncClientManager clientManager, org.apache.thrift.transport.TNonblockingTransport transport) {
      super(protocolFactory, clientManager, transport);
    }

    public void helloString(String para, org.apache.thrift.async.AsyncMethodCallback resultHandler) throws org.apache.thrift.TException {
      checkReady();
      helloString_call method_call = new helloString_call(para, resultHandler, this, ___protocolFactory, ___transport);
      this.___currentMethod = method_call;
      ___manager.call(method_call);
    }

1：TAsyncClientManager:异步客户端管理器类，AsyncClient统一把AsyncMethodCall传递给manager,内部用ConcurrentLinkedQueue,TimeOutSet,和另外开一个Thread来管理存储，消息的传递，接收，和超时处理，

并异常，完成时调用MethodCallback回调。

2：底层用Noblocking channel进行传递。

异步远程RPC调用：

public void helloString(String para, org.apache.thrift.async.AsyncMethodCallback resultHandler) throws org.apache.thrift.TException {
      checkReady();
      helloString_call method_call = new helloString_call(para, resultHandler, this, ___protocolFactory, ___transport);
      this.___currentMethod = method_call;
      ___manager.call(method_call);
    }

helloString_call类封装了消息表现形式：

 public static class helloString_call extends org.apache.thrift.async.TAsyncMethodCall {
      private String para;
      public helloString_call(String para, org.apache.thrift.async.AsyncMethodCallback resultHandler, org.apache.thrift.async.TAsyncClient client, org.apache.thrift.protocol.TProtocolFactory protocolFactory, org.apache.thrift.transport.TNonblockingTransport transport) throws org.apache.thrift.TException {
        super(client, protocolFactory, transport, resultHandler, false);
        this.para = para;
      }

      public void write_args(org.apache.thrift.protocol.TProtocol prot) throws org.apache.thrift.TException {
        prot.writeMessageBegin(new org.apache.thrift.protocol.TMessage("helloString", org.apache.thrift.protocol.TMessageType.CALL, 0));
        helloString_args args = new helloString_args();
        args.setPara(para);
        args.write(prot);
        prot.writeMessageEnd();
      }

      public String getResult() throws org.apache.thrift.TException {
        if (getState() != org.apache.thrift.async.TAsyncMethodCall.State.RESPONSE_READ) {
          throw new IllegalStateException("Method call not finished!");
        }
        org.apache.thrift.transport.TMemoryInputTransport memoryTransport = new org.apache.thrift.transport.TMemoryInputTransport(getFrameBuffer().array());
        org.apache.thrift.protocol.TProtocol prot = client.getProtocolFactory().getProtocol(memoryTransport);
        return (new Client(prot)).recv_helloString();
      }
    }

  }

异步RPC调用状态：

  public static enum State {
    CONNECTING, // connecting.连接
    WRITING_REQUEST_SIZE, // writing_request_size.写请求长度
    WRITING_REQUEST_BODY, // writing_request_body.写请求体
    READING_RESPONSE_SIZE, // reading_repsonse_size.读返回长度
    READING_RESPONSE_BODY, //reading_response_body.读返回体
    RESPONSE_READ, //repsonse_read.返回读取完毕
    ERROR;// error.有异常
  }

消息类型：

public final class TMessageType {
  public static final byte CALL  = 1; // 调用
  public static final byte REPLY = 2; //返回应答
  public static final byte EXCEPTION = 3;//异常
  public static final byte ONEWAY = 4;// 单向
}

Async服务器端处理，TBaseAsyncProcessor.process()：

 //Find processing function
        final TMessage msg = in.readMessageBegin();
        AsyncProcessFunction fn = processMap.get(msg.name);
 //Get Args
        TBase args = (TBase)fn.getEmptyArgsInstance();
         args.read(in);
         in.readMessageEnd();
        //start off processing function
        fn.start(iface, args,fn.getResultHandler(fb,msg.seqid));
        return true;

public static class helloString<I extends AsyncIface> extends org.apache.thrift.AsyncProcessFunction<I, helloString_args, String>

  public helloString_args getEmptyArgsInstance() {
        return new helloString_args();
      }

   public void start(I iface, helloString_args args, org.apache.thrift.async.AsyncMethodCallback<String> resultHandler) throws TException {
        iface.helloString(args.para,resultHandler);
      }

 public AsyncMethodCallback<String> getResultHandler(final AsyncFrameBuffer fb, final int seqid) {
        final org.apache.thrift.AsyncProcessFunction fcall = this;
        return new AsyncMethodCallback<String>() {
          public void onComplete(String o) {
            helloString_result result = new helloString_result();
            result.success = o;
            try {
              fcall.sendResponse(fb,result, org.apache.thrift.protocol.TMessageType.REPLY,seqid);
              return;
            } catch (Exception e) {
              LOGGER.error("Exception writing to internal frame buffer", e);
            }
            fb.close();
          }
          public void onError(Exception e) {
            byte msgType = org.apache.thrift.protocol.TMessageType.REPLY;
            org.apache.thrift.TBase msg;
            helloString_result result = new helloString_result();
            {
              msgType = org.apache.thrift.protocol.TMessageType.EXCEPTION;
              msg = (org.apache.thrift.TBase)new org.apache.thrift.TApplicationException(org.apache.thrift.TApplicationException.INTERNAL_ERROR, e.getMessage());
            }
            try {
              fcall.sendResponse(fb,msg,msgType,seqid);
              return;
            } catch (Exception ex) {
              LOGGER.error("Exception writing to internal frame buffer", ex);
            }
            fb.close();
          }
        };
      }

      protected boolean isOneway() {
        return false;
      }

TProcessor, TTransport, async, schema,  server分析待续。