Protobuf反射（java版）

水深无声 2021-05-14 11:35 733阅读 0赞

先看下代码：

public static void generateMsg() {
    		// 构造
    		com.google.protobuf.DescriptorProtos.FileDescriptorProto.Builder fileDesProtoBuilder = FileDescriptorProto
    				.newBuilder();
    		fileDesProtoBuilder.setSyntax("proto3");
    		fileDesProtoBuilder.setName("food.proto");// proto文件
    		Builder fileOptionBuilder = FileOptions.newBuilder();
    		fileOptionBuilder.setJavaPackage("com.lanjingling.pair");
    		fileOptionBuilder.setJavaOuterClassname("Food");
    		fileDesProtoBuilder.setOptions(fileOptionBuilder.build());
    
    		com.google.protobuf.DescriptorProtos.DescriptorProto.Builder addMessageTypeBuilder = fileDesProtoBuilder
    				.addMessageTypeBuilder();
    		addMessageTypeBuilder.setName("Pair");// message name
    
    		com.google.protobuf.DescriptorProtos.FieldDescriptorProto.Builder fidldDesProtoBuilder = FieldDescriptorProto
    				.newBuilder();
    		fidldDesProtoBuilder.setName("key");
    		fidldDesProtoBuilder.setTypeName("string");
    		fidldDesProtoBuilder.setNumber(1);
    		addMessageTypeBuilder.addField(fidldDesProtoBuilder.build());
    
    		com.google.protobuf.DescriptorProtos.FieldDescriptorProto.Builder fidldDesProtoBuilder1 = FieldDescriptorProto
    				.newBuilder();
    		fidldDesProtoBuilder1.setName("value");
    		fidldDesProtoBuilder1.setTypeName("int32");
    		fidldDesProtoBuilder1.setNumber(2);
    		addMessageTypeBuilder.addField(fidldDesProtoBuilder1.build());
    
    		FileDescriptorProto build = fileDesProtoBuilder.build();
    
    		// 创建
    		com.google.protobuf.DynamicMessage.Builder newBuilder = DynamicMessage
    				.newBuilder(build);
    		DynamicMessage build2 = newBuilder.build();
    		System.out.println(build2);
    		// TODO 上面的方式无法将消息生成对应的java类
    		// 可以使用protoc命令生成java类，然后使用class load将类加载到jvm
    
    		// 反射
    		try {
    			Class cl = Class.forName("com.lanjingling.pair.Food.$Pair");
    			Method method = cl.getMethod("newBuilder");
    			Object obj = method.invoke(null, new Object[] {});
    			Message.Builder msgBuilder = (Message.Builder) obj;
    			buildMessage(msgBuilder,new HashMap<>());
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    	}
    
    	public static void buildMessage(Message.Builder msgBuilder,Map<String, String> map) {
    		Descriptors.Descriptor descriptor = msgBuilder.getDescriptorForType();
    		for (Map.Entry<String, String> entry : map.entrySet()) {
    			Descriptors.FieldDescriptor filedDescriptor = descriptor.findFieldByName(entry.getKey());
    			if (filedDescriptor == null) {
    				continue;
    			}
    			boolean isRepeated = filedDescriptor.isRepeated();
    			Descriptors.FieldDescriptor.JavaType type = filedDescriptor.getJavaType();
    			if (isRepeated) {
    				String value = entry.getValue();
    				String[] strArray = value.split(",");
    				for (int i = 0; i < strArray.length; ++i) {
    					Object valueObject = getObject(strArray[i], type); // getObject
    					if (valueObject == null) {
    						continue;
    					}
    					msgBuilder.addRepeatedField(filedDescriptor, valueObject);
    				}
    			} else {
    				Object valueObject = getObject(entry.getValue(), type);
    				if (valueObject == null) {
    					continue;
    				}
    				msgBuilder.setField(filedDescriptor,
    						getObject(entry.getValue(), type));
    			}
    		}
    		Message msg = msgBuilder.build();
    	}
    
    	private static Object getObject(String rawString,
    			Descriptors.FieldDescriptor.JavaType type) {
    		try {
    			switch (type) {
    			case INT:
    				return Integer.valueOf(rawString);
    			case LONG:
    				return Long.valueOf(rawString);
    			case FLOAT:
    				return Float.valueOf(rawString);
    			case DOUBLE:
    				return Double.valueOf(rawString);
    			case BOOLEAN:
    				return Boolean.valueOf(rawString);
    			case STRING:
    				return rawString;
    			default:
    				// BYTE_STRING, ENUM, MESSAGE 哈哈先支持以上这些啦
    				return null;
    			}
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    		return null;
    	}

代码流程：

1）利用FileDescriptorProto、FieldDescriptorProto等类，来构造一个proto消息；构造完打印结果如下：

name: "food.proto"
    message_type {
      name: "Pair"
      field {
        name: "key"
        number: 1
        type_name: "string"
      }
      field {
        name: "value"
        number: 2
        type_name: "int32"
      }
    }
    options {
      java_package: "com.lanjingling.pair"
      java_outer_classname: "Food"
    }
    syntax: "proto3"

2）接下来，想找一个api将上面的proto消息动态编译，生成java源文件，然后加载类到jvm中。可惜java版本的protobuf没有找到这样的api（C++中有），那么这里只能是先将proto结构保存到文件中，然后用命令行的方式生成，然后加载了，代码如下：

String protoCMD="protoc --java_out=./ ./food.ptoro"
    Process process = Runtime.getRuntime().exec(protocCMD);
    
    //加载到jvm

3）通过java反射的方式加载对应的proto消息类，然后对其进行写入值。。。在写入值得时候，可以根据类型等进行判断