对pojo做protobuf的直接编解码实现

protobuf的编解码具有性能高、传输数据量小、跨语言的特点。但按照protobuf官方文档 https://developers.google.com/protocol-buffers/docs/overview中说的，需要先用protoc编译器生成对应语言的编解码代理，然后再用代理build和parse数据。

在我的一个应用场景中，使用脚本根据配置直接生成java pojo源码和对应proto文件，并在pojo中加上自身的编解码方法。这样的话若采用调用protoc生成代理的策略显得十分笨拙，另外既然protobuf能用代理类去解编码数据，那理论上,直接编解码数据也是可以实现的，但遗憾的是google并没有提供这方面的文档说明。

经过一番google以后，在stackoverflow上有大神说Descriptor描述proto文件，也有用C++实现的直接编解码的代码，java方面的非常少哇，只有一位朋友分享出来了 http://blog.csdn.net/lufeng20/article/details/8736584在此表示十分感激。

下面是编解码代码的实现：

package miniserver.util;

import static miniserver.util.ReflectionUtil.gatherAllFields;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import com.google.protobuf.DescriptorProtos.FileDescriptorProto;
import com.google.protobuf.DescriptorProtos.FileDescriptorSet;
import com.google.protobuf.Descriptors.Descriptor;
import com.google.protobuf.Descriptors.DescriptorValidationException;
import com.google.protobuf.Descriptors.FieldDescriptor;
import com.google.protobuf.Descriptors.FileDescriptor;
import com.google.protobuf.DynamicMessage;
import com.google.protobuf.DynamicMessage.Builder;
import com.google.protobuf.InvalidProtocolBufferException;
import com.google.protobuf.Message;

public class ProtoParserOrBuilder {
	private Map<String, Descriptor> descriptors = null;
	private static final String TEMP_DIR = "D://";
	public static final String PROTOC_PATH = System.getProperty("user.dir")
			+ "/protoc/protoc.exe";
	private File descFile;

	public ProtoParserOrBuilder() {
		descriptors = new HashMap<String, Descriptor>();
	}

	public ProtoParserOrBuilder(File proto) {
		descriptors = new HashMap<String, Descriptor>();

		init(proto);
	}

	private void init(File proto) {
		if (descFile != null && descFile.exists()) {
			descFile.delete();
		}
		this.descFile = createDescripFile(proto);

		FileInputStream fin = null;
		try {
			fin = new FileInputStream(descFile);

			FileDescriptorSet descriptorSet = FileDescriptorSet.parseFrom(fin);

			for (FileDescriptorProto fdp : descriptorSet.getFileList()) {
				FileDescriptor fd = FileDescriptor.buildFrom(fdp,
						new FileDescriptor[] {});

				for (Descriptor descriptor : fd.getMessageTypes()) {
					String className = descriptor.getName();

					this.descriptors.put(className, descriptor);
				}
			}

		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (DescriptorValidationException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} finally {
			try {
				if (fin != null) {
					fin.close();
				}
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}

	private File createDescripFile(File proto) {
		try {
			Runtime run = Runtime.getRuntime();
			String descFileName = System.currentTimeMillis()
					+ "FastProtoParser.desc";
			String protoPath = proto.getCanonicalPath();
			String protoFPath = proto.getParentFile().getAbsolutePath();

			String cmd = PROTOC_PATH + " -I=" + protoFPath
					+ " --descriptor_set_out=" + TEMP_DIR + descFileName + " "
					+ protoPath;
			System.out.println(cmd);

			// 如果不正常终止, 则生成desc文件失败
			Process p = run.exec(cmd);
			if (p.waitFor() != 0) {
				if (p.exitValue() == 1) {// p.exitValue()==0表示正常结束，1：非正常结束
					throw new RuntimeException("protoc 编译器报错");
				}
			}

			return new File(TEMP_DIR + descFileName);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return null;

	}

	public <T> T parse(Class<T> clazz, byte[] bytes) {
		String className = clazz.getSimpleName();
		Descriptor desc = this.descriptors.get(className);

		Map<String, String> fields = new HashMap<String, String>();
		try {
			DynamicMessage message = DynamicMessage.parseFrom(desc, bytes);
			Map<FieldDescriptor, Object> fieldDescs = message.getAllFields();
			for (Map.Entry<FieldDescriptor, Object> entry : fieldDescs
					.entrySet()) {
				fields.put(entry.getKey().getName(), entry.getValue()
						.toString());
			}

			T instance = clazz.newInstance();

			List<Field> fieldList = ReflectionUtil.gatherAllFields(clazz);
			for (Field f : fieldList) {
				ReflectionUtil.fillField(fields, instance, f);
			}

			return instance;
		} catch (InvalidProtocolBufferException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (InstantiationException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

		return null;

	}

	public byte[] build(Object obj) {

		Class<? extends Object> clazz = obj.getClass();
		String className = clazz.getSimpleName();

		Descriptor desc = this.descriptors.get(className);

		Builder builder = DynamicMessage.newBuilder(desc);
		List<FieldDescriptor> fieldDescs = desc.getFields();
		List<Field> fields = gatherAllFields(clazz);
		try {
			Map<String, Object> fieldValues = new HashMap<String, Object>();
			for (Field field : fields) {
				field.setAccessible(true);
				String fieldName = field.getName();
				Object fieldValueObject;
				fieldValueObject = field.get(obj);
				if (fieldValueObject != null) {
					fieldValues.put(fieldName, fieldValueObject);
				}
			}

			for (FieldDescriptor fieldDesc : fieldDescs) {
				String fieldName = fieldDesc.getName();
				Object val = fieldValues.get(fieldName);
				if (val != null) {
					builder.setField(fieldDesc, val);
				}
			}

			Message message = builder.build();

			return message.toByteArray();
		} catch (IllegalArgumentException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return null;
	}

	@Override
	protected void finalize() throws Throwable {
		super.finalize();

		this.descFile.delete();
	}

}

已经经过验证，与代理类生成的数据是一模一样的，解析也没有问题，请放心使用。

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