java - 让构建器返回具有相同字段的两个不同 POJO 的对象的最佳方法是什么

Question

POJO1

@Builder
Class POJO1 
{ 
   private String astring;
   private String bstring;
}

POJO2

@Builder
Class POJO2
{
   private String astring;
   private String bstring;
}

构建器方法

private POJO1 buildPOJO()
{
   return POJO1.builder().withaString().withbString().build();
}

我想要什么

POJO1 pojo = buildPOJO();
POJO2 pojo = buildPOJO(); // Same method to build both pojo's

<小时/>

我的代码中有这两个 pojo。我必须在几个地方 build 它们。两个 pojo 总是包含相同的字段，并且字段的数量也很大。我必须构建一个 buildPOJO 方法，通过它我可以创建两个 POJO 的对象。我没有明确的想法，但因为这些领域总是相似的。类型转换或任何其他方式有助于实现这一目标吗？

Answer 1

通过代理包装器，您可以使用通用接口(interface)，而无需在类中实现它。将公共(public) setter 提取到接口(interface)并在构建器中使用它来设置公共(public)字段。

代理代码最少:

public class Wrapper<T> implements InvocationHandler {
    private final T delegate;

    public Wrapper(T delegate) {
        this.delegate = delegate;
    }

    public static <T, I> I proxy(T delegate, Class<I> facade) {
        return (I) Proxy.newProxyInstance(
            facade.getClassLoader(),
            new Class[] { facade },
            new Wrapper(delegate)
        );
    }

    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        return delegate.getClass().getDeclaredMethod(method.getName(), method.getParameterTypes()).invoke(delegate, args);
    }
}

并且足够简单，可以在构建器中使用:

class PojoBuilder {
    private String foo;
    private int bar;
    private String a, b;

    public PojoBuilder withFoo(String foo) {
        this.foo = foo;
        return this;
    }

    public PojoBuilder withBar(int bar) {
        this.bar = bar;
        return this;
    }

    public PojoBuilder withA(String a) {
        this.a = a;
        return this;
    }

    public PojoBuilder withB(String b) {
        this.b = b;
        return this;
    }

    public PojoA buildA() {
        PojoA a = new PojoA();
        buildCommon(Wrapper.proxy(a, Pojo.class));
        a.setA(this.a);
        return a;
    }

    public PojoB buildB() {
        PojoB b = new PojoB();
        buildCommon(Wrapper.proxy(b, Pojo.class));
        b.setB(this.b);
        return b;
    }

    private void buildCommon(Pojo common) {
        common.setFoo(foo);
        common.setBar(bar);
    }
}

// Common setters for all pojos
interface Pojo {
    void setFoo(String foo);
    void setBar(int bar);
}

// One of the pojos.
// Note that this doesn't actually implement Pojo
class PojoA {
    private String foo;
    private int bar;
    private String a;

    public String getFoo() {
        return foo;
    }

    public void setFoo(String foo) {
        this.foo = foo;
    }

    public int getBar() {
        return bar;
    }

    public void setBar(int bar) {
        this.bar = bar;
    }

    public String getA() {
        return a;
    }

    public void setA(String a) {
        this.a = a;
    }
}

class PojoB {
    private String foo;
    private int bar;
    private String b;

    public String getFoo() {
        return foo;
    }

    public void setFoo(String foo) {
        this.foo = foo;
    }

    public int getBar() {
        return bar;
    }

    public void setBar(int bar) {
        this.bar = bar;
    }

    public String getB() {
        return b;
    }

    public void setB(String b) {
        this.b = b;
    }
}