Builder(构造器模式)示例

今天在看Hystrix源码时看了builder模式，为什么会这样使用呢？当构造器中的参数很多时，并且参数的顺序会给人造成困扰的时候，那么使用建造者模式来创建不可变类就是非常好的方法了。直接上代码，废话不多说。

调用入口

 public MetaHolder create(Object proxy, Method method, Object obj, Object[] args, final     
      ProceedingJoinPoint joinPoint) {
            HystrixCommand hystrixCommand = method.getAnnotation(HystrixCommand.class);
            ExecutionType executionType = ExecutionType.getExecutionType(method.getReturnType());
            MetaHolder.Builder builder = metaHolderBuilder(proxy, method, obj, args, joinPoint);
            if (isCompileWeaving()) {
                builder.ajcMethod(getAjcMethodFromTarget(joinPoint));
            }
            return builder.defaultCommandKey(method.getName())
                            .hystrixCommand(hystrixCommand)
                            .observableExecutionMode(hystrixCommand.observableExecutionMode())
                            .executionType(executionType)
                            .observable(ExecutionType.OBSERVABLE == executionType)
                            .build();

MetaHolder.Builder metaHolderBuilder(Object proxy, Method method, Object obj, Object[] args, final ProceedingJoinPoint joinPoint) {
            MetaHolder.Builder builder = MetaHolder.builder()
                    .args(args).method(method).obj(obj).proxyObj(proxy)
                    .joinPoint(joinPoint);

            setFallbackMethod(builder, obj.getClass(), method);
            builder = setDefaultProperties(builder, obj.getClass(), joinPoint);
            return builder;
        }

public final class MetaHolder {

    private final HystrixCollapser hystrixCollapser;
    private final HystrixCommand hystrixCommand;
    private final DefaultProperties defaultProperties;

    private final Method method;
    private final Method cacheKeyMethod;
    private final Method ajcMethod;
    private final Method fallbackMethod;
    private final Object obj;
    private final Object proxyObj;
    private final Object[] args;
    private final Closure closure;
    private final String defaultGroupKey;
    private final String defaultCommandKey;
    private final String defaultCollapserKey;
    private final String defaultThreadPoolKey;
    private final ExecutionType executionType;
    private final boolean extendedFallback;
    private final ExecutionType collapserExecutionType;
    private final ExecutionType fallbackExecutionType;
    private final boolean fallback;
    private boolean extendedParentFallback;
    private final JoinPoint joinPoint;
    private final boolean observable;
    private final ObservableExecutionMode observableExecutionMode;

    private MetaHolder(Builder builder) {
        this.hystrixCommand = builder.hystrixCommand;
        this.method = builder.method;
        this.cacheKeyMethod = builder.cacheKeyMethod;
        this.fallbackMethod = builder.fallbackMethod;
        this.ajcMethod = builder.ajcMethod;
        this.obj = builder.obj;
        this.proxyObj = builder.proxyObj;
        this.args = builder.args;
        this.closure = builder.closure;
        this.defaultGroupKey = builder.defaultGroupKey;
        this.defaultCommandKey = builder.defaultCommandKey;
        this.defaultThreadPoolKey = builder.defaultThreadPoolKey;
        this.defaultCollapserKey = builder.defaultCollapserKey;
        this.defaultProperties = builder.defaultProperties;
        this.hystrixCollapser = builder.hystrixCollapser;
        this.executionType = builder.executionType;
        this.collapserExecutionType = builder.collapserExecutionType;
        this.fallbackExecutionType = builder.fallbackExecutionType;
        this.joinPoint = builder.joinPoint;
        this.extendedFallback = builder.extendedFallback;
        this.fallback = builder.fallback;
        this.extendedParentFallback = builder.extendedParentFallback;
        this.observable = builder.observable;
        this.observableExecutionMode = builder.observableExecutionMode;
    }


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


public static final class Builder {

        private HystrixCollapser hystrixCollapser;
        private HystrixCommand hystrixCommand;
        private DefaultProperties defaultProperties;
        private Method method;
        private Method cacheKeyMethod;
        private Method fallbackMethod;
        private Method ajcMethod;
        private Object obj;
        private Object proxyObj;
        private Closure closure;
        private Object[] args;
        private String defaultGroupKey;
        private String defaultCommandKey;
        private String defaultCollapserKey;
        private String defaultThreadPoolKey;
        private ExecutionType executionType;
        private ExecutionType collapserExecutionType;
        private ExecutionType fallbackExecutionType;
        private boolean extendedFallback;
        private boolean fallback;
        private boolean extendedParentFallback;
        private boolean observable;
        private JoinPoint joinPoint;
        private ObservableExecutionMode observableExecutionMode;

        public Builder hystrixCollapser(HystrixCollapser hystrixCollapser) {
            this.hystrixCollapser = hystrixCollapser;
            return this;
        }

        public Builder hystrixCommand(HystrixCommand hystrixCommand) {
            this.hystrixCommand = hystrixCommand;
            return this;
        }

        public Builder method(Method method) {
            this.method = method;
            return this;
        }

        public Builder cacheKeyMethod(Method cacheKeyMethod) {
            this.cacheKeyMethod = cacheKeyMethod;
            return this;
        }

        public Builder fallbackMethod(Method fallbackMethod) {
            this.fallbackMethod = fallbackMethod;
            return this;
        }

        public Builder fallbackExecutionType(ExecutionType fallbackExecutionType) {
            this.fallbackExecutionType = fallbackExecutionType;
            return this;
        }

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

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

        public Builder ajcMethod(Method ajcMethod) {
            this.ajcMethod = ajcMethod;
            return this;
        }

        public Builder obj(Object obj) {
            this.obj = obj;
            return this;
        }

        public Builder proxyObj(Object proxy) {
            this.proxyObj = proxy;
            return this;
        }

        public Builder args(Object[] args) {
            this.args = args;
            return this;
        }

        public Builder closure(Closure closure) {
            this.closure = closure;
            return this;
        }

        public Builder executionType(ExecutionType executionType) {
            this.executionType = executionType;
            return this;
        }

        public Builder collapserExecutionType(ExecutionType collapserExecutionType) {
            this.collapserExecutionType = collapserExecutionType;
            return this;
        }

        public Builder defaultGroupKey(String defGroupKey) {
            this.defaultGroupKey = defGroupKey;
            return this;
        }

        public Builder defaultCommandKey(String defCommandKey) {
            this.defaultCommandKey = defCommandKey;
            return this;
        }

        public Builder defaultThreadPoolKey(String defaultThreadPoolKey) {
            this.defaultThreadPoolKey = defaultThreadPoolKey;
            return this;
        }

        public Builder defaultCollapserKey(String defCollapserKey) {
            this.defaultCollapserKey = defCollapserKey;
            return this;
        }

        public Builder defaultProperties(@Nullable DefaultProperties defaultProperties) {
            this.defaultProperties = defaultProperties;
            return this;
        }

        public Builder joinPoint(JoinPoint joinPoint) {
            this.joinPoint = joinPoint;
            return this;
        }

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

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

        public Builder observableExecutionMode(ObservableExecutionMode observableExecutionMode) {
            this.observableExecutionMode = observableExecutionMode;
            return this;
        }

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


    }