我最近在我的一个项目中开始使用Builder模式，我正在尝试在Builder类中添加某种验证。我假设我们不能在编译时这样做，所以这就是我在运行时进行此验证的原因。但可能是我错了，这就是我想看看我是否可以在编译时这样做。
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：
在我上面的构建器模式中，我只有一个参数必需clientId，其余参数是可选的，但我需要设置userid，flowid或deviceid 。如果这三个都没有设置，那么我向IllegalStateException抛出一条错误消息，如上面的代码中所示。那个检查我在运行时做的。如果可能的话，我想在编译时进行此检查，除非提供所有内容，否则不要构建我的模式？
并非强制要求他们每次都会传递所有这三个id，他们可以传递所有三个或有时两个或有时只传递一个，但条件是其中一个应该被设置。
如何改进构建器模式，以便我只能在编译时进行id验证，而不是在运行时执行此操作？
我发现了这个SO link，它确实谈到同样的事情，但不确定如何在我的场景中使用它？还有builder pattern with a twist和此SO question
任何人都可以提供一个示例，我如何在构建器模式中修复此问题？
答案 0 :(得分：1)
只有在设置了必需的属性时才能访问build方法：
public class Builders {
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
Builder b = new Builder(123);
// Builded instance1 = b
// .defFlag(false)
// .build(); // compile error
Builder c1 = b
.refFlag(true);
Builded instance2 = b
.setDeviceId("device id") // here's the magic, without this call `build` method would be unaccessible
.build();
Builded instance3 = b
.refFlag(false)
.defFlag(true)
.setDeviceId("device id")
.setUserId(12)
.build();
System.out.printf("%s\n%s\n", instance2, instance3);
}
}
class Builded implements Cloneable {
int clientId;
Long userid;
String deviceid;
String flowid;
boolean defFlag;
boolean refFlag;
public Builded(int clientId) {
this.clientId = clientId;
}
@Override
protected Object clone() throws CloneNotSupportedException {
return (Builded) super.clone();
}
@Override
public String toString() {
return String.format("{c: %d, u: %d, d: %s, f: %s, df: %b, rf: %b}", clientId, userid, deviceid, flowid, defFlag, refFlag);
}
}
class Builder {
int clientId;
protected Builded instance;
private Builder() {
}
protected Builder(int clientId) {
this.clientId = clientId;
prepare();
}
protected final void prepare() {
instance = new Builded(clientId);
}
private Builded build() {
try {
return (Builded) instance.clone();
} catch (CloneNotSupportedException ex) {
throw new RuntimeException(ex);
}
}
public Builder defFlag(boolean defFlag) {
instance.defFlag = defFlag;
return this;
}
public Builder refFlag(boolean refFlag) {
instance.refFlag = refFlag;
return this;
}
public SubBuilder setUserId(long userid) {
instance.userid = userid;
return new SubBuilder(instance);
}
public SubBuilder setDeviceId(String deviceid) {
instance.deviceid = deviceid;
return new SubBuilder(instance);
}
public SubBuilder setFlowId(String flowid) {
instance.flowid = flowid;
return new SubBuilder(instance);
}
public static class SubBuilder extends Builder {
private SubBuilder(Builded instance) {
this.instance = instance;
}
public Builded build() {
return super.build();
}
}
}
输出：
{c: 123, u: null, d: device id, f: null, df: false, rf: true}
{c: 123, u: 12, d: device id, f: null, df: true, rf: false}