使用GSON在Java中打开.txt文件

Question

When I run the following code to save a JSON:

String regionObject = this.gson.toJson(parentRegion);
JsonFileInputOutput.saveObjectToTextFile(regionObject,
    "./tests/model/util/test_saveRegionObject.txt");  

and after that I reopen the created .txt file:

public void test_openRegionObject() throws IOException {
String regionAsString = JsonFileInputOutput
    .openObjectInTextFile("./tests/model/util/test_saveRegionObject.txt");
Gson gson = new Gson();
Region LGNRegion = gson.fromJson(regionAsString, Region.class);
System.out.println(LGNRegion.toString());
}

it works perfectly fine.

However, when I try the second snippet of code into a different class that does not contain the first one I get the following error:

java.lang.RuntimeException Failed to invoke public model.MARK_II.Cell() with no args

Cell is a custom class that is used inside Region class. Here is the implementation of the Cell class:

public abstract class Cell {
protected boolean isActive;

public Cell() {
this.isActive = false;
}

public boolean getActiveState() {
return this.isActive;
}

public void setActiveState(boolean isActive) {
this.isActive = isActive;
}

}

My question is how can I fix this exception so that I can read a proper serialized JSON as the one I create with first snippet of code.

Answer 1

Two questions here.

1. Why I get the exception? This is simple to answer: your Cell class (or better your subclass of Cell class since Cell is abstract) has no a constructor without parameters. Maybe it has a constructor with one or more parameters.

2. Why I can't open a generic file? Difficult to say without showing us the file. It's sure that if you save a Json serialization into a file and just open it you have no error. My best guess is this: when you serialize and save you have not Cell subclasses inside (maybe member variables are nulls), whenever you open another file, maybe Cell subclasses are defined and so answer to 1. applies.