feat(Java_ConstractUtil):添加测试方法，修改bug（反射处理null出现空指针的问题比较多），创建抽象类和继承使用示例。添加readme修改记录

src/main/test/SimpleListObj.java

@@ -0,0 +1,55 @@
+import java.util.Date;
+import java.util.List;
+
+public class SimpleListObj {
+
+    int x;
+
+    String y;
+
+    float m;
+
+    Date date;
+
+    List<String> list;
+
+    public int getX() {
+        return x;
+    }
+
+    public void setX(int x) {
+        this.x = x;
+    }
+
+    public String getY() {
+        return y;
+    }
+
+    public void setY(String y) {
+        this.y = y;
+    }
+
+    public float getM() {
+        return m;
+    }
+
+    public void setM(float m) {
+        this.m = m;
+    }
+
+    public Date getDate() {
+        return date;
+    }
+
+    public void setDate(Date date) {
+        this.date = date;
+    }
+
+    public List<String> getList() {
+        return list;
+    }
+
+    public void setList(List<String> list) {
+        this.list = list;
+    }
+}