英文:
How to solve NULL pointer error when using Jackson 1.x
问题
以下是您要求的翻译部分：
我使用一个API来请求数据。对于一个请求，当我尝试将值设置为int时，我收到一个空指针异常。
public class Player implements Serializable {
// ...
// ...
@JsonProperty("offsides")
private Integer offsides;
@JsonProperty("offsides")
public Integer getOffsides() {
return offsides;
}
@JsonProperty("offsides")
public void setOffsides(Integer offsides) {
this.offsides = offsides;
}
// ...
}
public class Fixtures {
private final static long serialVersionUID = 2571183788260356219L;
public static void main(String args[]) throws Exception {
ObjectMapper mapper = new ObjectMapper();
// ...
FixtureJSONMapp fixturesFixtures = mapper.readValue(fixturesFile, FixtureJSONMapp.class);
List<String> insertStatus = FixturesFixturesInsert.insertAllFixtures(fixturesFixtures,
statsNumb, playersNumb, eventsNumb, lineupsNumb);
}
}
public class FixturesFixturesInsert {
public static List<String> insertAllFixtures(FixtureJSONMapp fixturesFixtures, int statsNumb, int playersNumb, int eventsNumb, int lineupsNumb) throws Exception {
try {
Connection con = dbConnector.ConnectToDB();
PreparedStatement pstmtFixtures = con.prepareStatement(".....");
for (int i = 0; i < fixturesFixtures.getApi().getFixtures().size(); i++) {
// ...
int offsides = fixturesFixtures.getApi().getFixtures().get(i).getPlayers().get(j).getOffsides();
// ...
}
}
// ...
}
}
对于"int offsides"，在这种情况下，我得到了一个空指针异常。我可以通过以下方式解决：
int offsides = (fixtures....getOffsides() != null ? getOffsides() : 0);
但我认为我应该能够使用mapper.getSerializationConfig().setSerializationInclusion(Inclusion.NON_NULL);或类似的方法，但我无法使其工作。我希望能够在更多地方设置这个设置，因为我将不得不在许多地方这样做。
我想在收到的JSON字符串中，如果值为NULL，将其设置为0。这种做法是否可行？正如主题中提到的，我使用Jackson 1.x（org.codehaus.jackson）。
英文:
I use an API from where I request data. For one request I receive a NULL pointer exception when I try to set the value to an int.
public class Player implements Serializable {
...
...
...
...
@JsonProperty("offsides")
private Integer offsides;
...
...
@JsonProperty("offsides")
public Integer getOffsides() {
return offsides;
}
@JsonProperty("offsides")
public void setOffsides(Integer offsides) {
this.offsides = offsides;
}
...
public class Fixtures {
private final static long serialVersionUID = 2571183788260356219L;
public static void main(String args[]) throws Exception {
ObjectMapper mapper = new ObjectMapper();
...
...
...
FixtureJSONMapp fixturesFixtures = mapper.readValue(fixturesFile, FixtureJSONMapp.class);
List<String> insertStatus = FixturesFixturesInsert.insertAllFixtures(fixturesFixtures,
statsNumb, playersNumb, eventsNumb, lineupsNumb);
}
}
...
public class FixturesFixturesInsert {
public static List<String> insertAllFixtures(FixtureJSONMapp fixturesFixtures, int statsNumb, int playersNumb, int eventsNumb, int lineupsNumb) throws Exception {
try {
Connection con = dbConnector.ConnectToDB();
PreparedStatement pstmtFixtures = con.prepareStatement(".....");
for(int i = 0; i < fixturesFixtures.getApi().getFixtures().size(); i++) {
...
...
...
...
int offsides = fixturesFixtures.getApi().getFixtures().get(i).getPlayers().get(j).getOffsides();
...
}
}
It is for the "int offsides" I get an NULL pointer exception in this case. I can solve by
int offsides = (fixtures....getOffsides() != null ? getOffsides() : 0);
But I thought I should be able to use mapper.getSerializationConfig().setSerializationInclusion(Inclusion.NON_NULL); or something similar but I can´t get it to work. I would like to set this setting more global because I will have to do it in many places.
I would like to set value to 0 if it is NULL in the JSON String i receive. Is this possible to do?
As mentioned in the subject I use Jackson 1.x (org.codehaus.jackson)
答案1
得分: 1
首先确保 setSerializationInclusion(...) 应用于传入数据。我不这么认为，它对即将发送的数据生效。
注意：
- 即使它生效了，你正试图访问
null并将其赋值给一个基本类型。 NullPointerException表明你在一个null对象上调用了getOffsides()，即null.getOffsides()- 如果你至少在使用 Java 8，你可以使用
Optional.ofNullable在其为null时将int offsides设置为0。
英文:
First of make sure that setSerializationInclusion(...) is applied on an incoming data. I don't think so, it takes effect for data you are about to send.
NOTE:
- Even if it works, you are trying to access
nulland assign it to a primitive. NullPointerExceptiontells that you are callinggetOffsides()on anullobject. i.e.null.getOffsides()- If you are using atleast Java 8, you can use
Optional.ofNullableto setint offsidesto0whenever it isnull
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