Java使用protobuf时,往往需要在Java对象(比如POJO)和protobuf message的Java对象间互转:

1. protobuf接口需要传入message参数: 把POJO转成message, 作为接口参数;
2. protobuf接口会返回message参数: 需要把message转成POJO, 供后续使用.

比如:
protobuf的message

message HelloRequest {
    string name = 1;
    int32 type = 2;
    string location = 3;
    bool flag = 4;
}

Java的POJO:

@Getter
@Setter
@ToString
public class HelloDTO {
    private String name;
    private Integer type;
    private String location;
    private Boolean flag;
    private String message;
}

POJO -> Message

Hello.HelloRequest.Builder builder = Hello.HelloRequest.newBuilder();
builder.setFlag(true);
builder.setName("Name1");
builder.setLocation("Location1");
builder.setType(1);
Hello.HelloRequest request = builder.build();

Message -> POJO

Hello.HelloRequest request;
HelloDTO hello = new HelloDTO();
hello.setFlag(request.getFlag());
hello.setName(request.getName());
hello.setLocation(request.getLocation());
hello.setType(request.getType());

可以想象, 在protobuf定义的message很多的情况下,这些代码写起来费时费力, 还容易遗漏,有什么好的方法可以解决这个问题呢?
实际上POJO与PB Message之间的转换, 类似于POJO与Json之间的转换, 所以可以把上述过程简化:

message -> POJO: 对于POJO中任一属性,只有message中也有时, 才取出来设置.

/**
     * ProtoBuffer object to POJO
     */
    private static <T> T fromProtoBuffer(GeneratedMessageV3 pbObject, Class<T> modelClass) {
        T model = null;

        try {
            model = modelClass.newInstance();
            Field[] modelFields = modelClass.getDeclaredFields();
            if (modelFields != null && modelFields.length > 0) {
                for (Field modelField : modelFields) {
                    String fieldName = modelField.getName();
                    String name = fieldName.substring(0, 1).toUpperCase() + fieldName.substring(1);

                    Class<?> fieldType = modelField.getType();
                    try {
                        Method pbGetMethod = pbObject.getClass().getMethod("get" + name);
                        Object value = pbGetMethod.invoke(pbObject);

                        Method modelSetMethod = modelClass.getMethod("set" + name, fieldType);
                        modelSetMethod.invoke(model, value);
                    } catch (NoSuchMethodException e) {
                        e.printStackTrace();
                    }
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }

        return model;
    }

POJO -> message: 对于message中任一属性,只有POJO中也有时, 才取出来设置.

    /**
     * POJO -> ProtoBuffer object
     */
    private static <T> T toProtoBuffer(Object model, Class<T> pbClass) {
        if (!GeneratedMessageV3.class.isAssignableFrom(pbClass)) {
            throw new RuntimeException("Not ProtoBuffer message type");
        }

        T pbObject = null;

        try {
            Object pbBuilder = pbClass.getDeclaredMethod("newBuilder").invoke(null);
            Field[] pbFields = pbClass.getDeclaredFields();
            if (pbFields != null && pbFields.length > 0) {
                for (Field pbField : pbFields) {
                    String fieldName = pbField.getName().substring(0, pbField.getName().length() - 1);
                    String name = fieldName.substring(0, 1).toUpperCase() + fieldName.substring(1);
                    Class<?> fieldType = pbField.getType();
                    if (pbField.getType() == Object.class) {
                        fieldType = String.class;
                    }

                    try {
                        Method modelGetMethod = model.getClass().getMethod("get" + name);
                        Object value = modelGetMethod.invoke(model);
                        if (value != null) {
                            Method pbBuilderSetMethod = pbBuilder.getClass().getMethod("set" + name, fieldType);
                            pbBuilderSetMethod.invoke(pbBuilder, value);
                        }
                    } catch (NoSuchMethodException e) {
                        e.printStackTrace();
                    }
                }
            }
            pbObject = (T) pbBuilder.getClass().getDeclaredMethod("build").invoke(pbBuilder);
        } catch (Exception e) {
            e.printStackTrace();
        }

        return pbObject;
    }

以上代码仅为示例代码(demo), 实际使用时往往message和POJO分别都是嵌套的, 因此需要略有调整.