使用Gson将对象数组写入文件

Question

public boolean wirteJson(Passenger passenger[]){
    try {
        file = new FileWriter(System.getProperty("user.dir")+"/"+fileName);
        for (int i = 0; i < 10; i++) {
            String json =gson.toJson(passenger[i]);
            file.write(json);
        }
        file.flush();
        file.close();

    } catch (IOException ex) {
        return false;
    }
    return false;
}

I'm trying to write the passenger array to a file with Gson. I'm open to alternatives.

Answer 1

You don't have to serialize the given input array by each element:

• Gson can do it all itself;
• your method assumes the input array is exactly 10 elements long (thus, throwing ArrayIndexOutOfBoundsException if the input array has less elements, or writing only first 10 elements);
• your method does not write well-formed JSON: {},{},{} is invalid, whilst [{},{},{}] is;
• your method, as suggested by RealSkeptic , does not need intermediate string representations.

All you need are just two methods Gson.toJson and Gson.fromJson . So, here is a simple example:

final class Passenger {

    final String name;

    Passenger(final String name) {
        this.name = name;
    }

}

public static void main(final String... args)
        throws IOException {
    final File file = createTempFile("q43439637_", "_q43439637");
    file.deleteOnExit();
    try ( final FileWriter fileWriter = new FileWriter(file) ) {
        final Passenger[] before = { new Passenger("Alice"), new Passenger("Bob") };
        gson.toJson(before, fileWriter);
    }
    try ( final FileReader fileReader = new FileReader(file) ) {
        final Passenger[] after = gson.fromJson(fileReader, Passenger[].class);
        for ( final Passenger p : after ) {
            System.out.println(p.name);
        }
    }
}

Output:

Alice
Bob

PS Your out-of- catch return seems to have to return true rather than false . Also, flush() is unnecessary before close() .