通过在编译时进行验证来改进构建器模式

Question

我最近开始在我的一个项目中使用 Builder 模式，我正在尝试在我的 Builder class 上添加某种验证。我假设我们不能在编译时执行此操作，所以这就是我在运行时执行此验证的原因。但可能是我错了，这就是我想看看我是否可以在编译时做到这一点。

传统生成器模式

public final class RequestKey {

    private final Long userid;
    private final String deviceid;
    private final String flowid;
    private final int clientid;
    private final long timeout;
    private final boolean abcFlag;
    private final boolean defFlag;
    private final Map<String, String> baseMap;

    private RequestKey(Builder builder) {
        this.userid = builder.userid;
        this.deviceid = builder.deviceid;
        this.flowid = builder.flowid;
        this.clientid = builder.clientid;
        this.abcFlag = builder.abcFlag;
        this.defFlag = builder.defFlag;
        this.baseMap = builder.baseMap.build();
        this.timeout = builder.timeout;
    }

    public static class Builder {
        protected final int clientid;
        protected Long userid = null;
        protected String deviceid = null;
        protected String flowid = null;
        protected long timeout = 200L;
        protected boolean abcFlag = false;
        protected boolean defFlag = true;
        protected ImmutableMap.Builder<String, String> baseMap = ImmutableMap.builder();

        public Builder(int clientid) {
            checkArgument(clientid > 0, "clientid must not be negative or zero");
            this.clientid = clientid;
        }

        public Builder setUserId(long userid) {
            checkArgument(userid > 0, "userid must not be negative or zero");
            this.userid = Long.valueOf(userid);
            return this;
        }

        public Builder setDeviceId(String deviceid) {
            checkNotNull(deviceid, "deviceid cannot be null");
            checkArgument(deviceid.length() > 0, "deviceid can't be an empty string");
            this.deviceid = deviceid;
            return this;
        }

        public Builder setFlowId(String flowid) {
            checkNotNull(flowid, "flowid cannot be null");
            checkArgument(flowid.length() > 0, "flowid can't be an empty string");
            this.flowid = flowid;
            return this;
        }

        public Builder baseMap(Map<String, String> baseMap) {
            checkNotNull(baseMap, "baseMap cannot be null");
            this.baseMap.putAll(baseMap);
            return this;
        }

        public Builder abcFlag(boolean abcFlag) {
            this.abcFlag = abcFlag;
            return this;
        }

        public Builder defFlag(boolean defFlag) {
            this.defFlag = defFlag;
            return this;
        }

        public Builder addTimeout(long timeout) {
            checkArgument(timeout > 0, "timeout must not be negative or zero");
            this.timeout = timeout;
            return this;
        }

        public RequestKey build() {
            if (!this.isValid()) {
                throw new IllegalStateException("You have to pass at least one"
                        + " of the following: userid, flowid or deviceid");
            }
            return new RequestKey(this);
        }

        private boolean isValid() {
            return !(TestUtils.isEmpty(userid) && TestUtils.isEmpty(flowid) && TestUtils.isEmpty(deviceid));
        }
    }

    // getters here
}

问题陈述：

如您所见，我有各种参数，但只有一个参数 clientId 是必需的，其余参数都是可选的。在我上面的代码中，我需要设置 userid、flowid 或 deviceid。如果设置了这三个中的 none，那么我将抛出 IllegalStateException 并显示一条错误消息，如上面的代码所示。如果所有三个或两个都已设置，那很好，我正在对这三个或两个执行一些优先级逻辑来决定使用哪一个，但至少必须设置其中一个。

他们不是必须每次都传递所有三个 id，他们可以传递所有三个，有时传递两个，有时只传递一个，但条件是应设置其中一个。

我正在寻找的是 - 除了在运行时做所有这些事情，我可以在编译时做这个并且不构建我的构建器模式，除非这三个中的任何一个被设置并且在编译时它应该告诉缺少什么？

我发现了这个 link which exactly talks about same thing but not sure how can I use it in my scenario? And also this builder pattern with a twist and this SO question

Answer 1

根据您的描述，我会采用您已经提到的解决方案： How to improve the builder pattern? and Builder pattern with a twist 略有不同：

这两种解决方案基本上都是链式构建器：你调用 Builder.create().firstMandatoryField() 它将 return 第二个必填字段的构建器实例，依此类推，直到你到达最后一个构建器，它具有调用私有构造函数的实际 build 方法。

对于您的情况，有些字段必须至少设置其中一个，这意味着您的第一个构建器将提供初始化它们的方法，return 第二个构建器的实例。然后，在第二个构建器上，您可以设置所有字段（可选字段和必填字段）。

这是实现此目的的一个版本：

public final class RequestKey {

    private final Long userid;
    private final String deviceid;
    private final String flowid;
    private final int clientid;
    private final long timeout;
    private final boolean abcFlag;
    private final boolean defFlag;
    private final Map<String, String> baseMap;

    private RequestKey(FinalBuilder builder) {
        this.userid = builder.userid;
        this.deviceid = builder.deviceid;
        this.flowid = builder.flowid;
        this.clientid = builder.clientid;
        this.abcFlag = builder.abcFlag;
        this.defFlag = builder.defFlag;
        this.baseMap = builder.baseMap.build();
        this.timeout = builder.timeout;
    }
    public static class Builder {
        public Builder1 clientId(int clientid) {
            checkArgument(clientid > 0, "clientid must not be negative or zero");
            return new Builder1(clientid);
        }
    }
    public static class Builder1 {
        private final int clientid;

        Builder1(int clientid){
            this.clientid = clientid;
        }
        public FinalBuilder userId(long userid) {
            checkArgument(userid > 0, "userid must not be negative or zero");
            FinalBuilder builder = new FinalBuilder(clientid);
            return builder.setUserId(userid);
        }

        public FinalBuilder deviceId(String deviceid) {
            checkNotNull(deviceid, "deviceid cannot be null");
            checkArgument(deviceid.length() > 0, "deviceid can't be an empty string");
            FinalBuilder builder = new FinalBuilder(clientid);
            return builder.setDeviceId(deviceid);
        }

        public FinalBuilder flowId(String flowid) {
            checkNotNull(flowid, "flowid cannot be null");
            checkArgument(flowid.length() > 0, "flowid can't be an empty string");
            FinalBuilder builder = new FinalBuilder(clientid);
            return builder.setFlowId(flowid);
        }
    }

    public static class FinalBuilder {
        private final int clientid;
        private Long userid = null;
        private String deviceid = null;
        private String flowid = null;
        private long timeout = 200L;
        private boolean abcFlag = false;
        private boolean defFlag = true;
        private ImmutableMap.Builder<String, String> baseMap = ImmutableMap.builder();

        FinalBuilder(int clientId) {
            this.clientid = clientId;
        }


        FinalBuilder setUserId(long userid) {
            this.userid = userid;
            return this;
        }

        FinalBuilder setDeviceId(String deviceid) {
            this.deviceid = deviceid;
            return this;
        }

        FinalBuilder setFlowId(String flowid) {
            this.flowid = flowid;
            return this;
        }
        public FinalBuilder userId(long userid) {
            checkArgument(userid > 0, "userid must not be negative or zero");
            this.userid = Long.valueOf(userid);
            this.userid = userid;
            return this;
        }

        public FinalBuilder deviceId(String deviceid) {
            checkNotNull(deviceid, "deviceid cannot be null");
            checkArgument(deviceid.length() > 0, "deviceid can't be an empty string");
            this.deviceid = deviceid;
            return this;
        }

        public FinalBuilder flowId(String flowid) {
            checkNotNull(flowid, "flowid cannot be null");
            checkArgument(flowid.length() > 0, "flowid can't be an empty string");
            this.flowid = flowid;
            return this;
        }

        public FinalBuilder baseMap(Map<String, String> baseMap) {
            checkNotNull(baseMap, "baseMap cannot be null");
            this.baseMap.putAll(baseMap);
            return this;
        }

        public FinalBuilder abcFlag(boolean abcFlag) {
            this.abcFlag = abcFlag;
            return this;
        }

        public FinalBuilder defFlag(boolean defFlag) {
            this.defFlag = defFlag;
            return this;
        }

        public FinalBuilder addTimeout(long timeout) {
            checkArgument(timeout > 0, "timeout must not be negative or zero");
            this.timeout = timeout;
            return this;
        }

        public RequestKey build() {
            return new RequestKey(this);
        }

    }
    public static Builder create() {
        return new Builder();
    }


    // getters here
}

然后你可以调用它：

RequestKey.create()
    .clientId(1234) // Builder of the first level for the mandatory field
    .userId(549375349) // Builder of the second level for any of the additional three mandatory fields
    .flowId("flow number") // Builder on the last level allows setting and overriding the three additional mandatory fields
    .timeout(3600*1000) // Builder on the last level allows setting of the optional fields
    .build(); // Create the instance

通过在编译时进行验证来改进构建器模式

Improving builder pattern by doing validations at compile time

java

design-patterns

builder

builder-pattern