5 ways to Filter and exclude Fastjson fields (including examples)

1. Specify fields that do not need serialization through annotations

Fields that do not need serialization can be excluded by annotating @jsonField (serialize = false).

public class DontSerializeAnnotation {

	@JSONField(serialize = false)
    private Long id;
    private String name;

    public Long getId(a) {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName(a) {
        return name;
    }

    public void setName(String name) {
        this.name = name; }}/** * specify fields that do not need serialization via annotations:@JSONField(serialize = false)
 */
@Test
public void testDontSerializeAnnotation(a) {
	DontSerializeAnnotation guestUser = new DontSerializeAnnotation();
	guestUser.setId(2L);
	guestUser.setName("guest");
	System.out.println(JSON.toJSONString(guestUser));
}

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Execution Result:

{"name":"guest"}
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2. Variables declared transient are not serialized

If the serialized field is decorated with transient, it will not be serialized.

public class TransientObject {

    private Long id;
    private transient String name;

    public Long getId(a) {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName(a) {
        return name;
    }

    public void setName(String name) {
        this.name = name; }}/** * variables declared transient are not serialized */
@Test
public void testTransientObject(a) {
	TransientObject guestUser = new TransientObject();
	guestUser.setId(2L);
	guestUser.setName("guest");
	System.out.println(JSON.toJSONString(guestUser));
}
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Execution Result:

{"id":2}
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3. Use property filters to exclude fields that do not need serialization

Using the SimplePropertyPreFilter, you can set 1 to more fields to filter out at once.

3.1 Filtering a Field in an Object

public class User {

    private Long id;
    private String name;

    public Long getId(a) {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName(a) {
        return name;
    }

    public void setName(String name) {
        this.name = name; }}/** * Use property filters to exclude fields that do not require serialization */
@Test
public void testExcludeSingleFilter(a) {
	User guestUser = new User();
	guestUser.setId(2L);
	guestUser.setName("guest");
	
	SimplePropertyPreFilter filter = new SimplePropertyPreFilter();
	filter.getExcludes().add("name"); // Exclude the field named name
	
	System.out.println(JSON.toJSONString(guestUser, filter));
}
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Execution Result:

{"id":2}
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3.2 Filtering fields of the same name in nested classes

The User in Group, refer to the previous section.

public class Group {

    private Long id;
    private String name;
    private List<User> users = new ArrayList<User>();

    public Long getId(a) {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName(a) {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public List<User> getUsers(a) {
        return users;
    }

    public void setUsers(List<User> users) {
        this.users = users;
    }

    public void addUser(User user) { users.add(user); }}/** * Use attribute filters to exclude fields that do not need to be serialized. * For nested classes, fields with the same name in different classes are filtered out. * /
@Test
public void testExcludeEmbedFilter(a) {
	Group group = new Group();
	group.setId(0L);
	group.setName("admin");

	User guestUser = new User();
	guestUser.setId(2L);
	guestUser.setName("guest");

	User rootUser = new User();
	rootUser.setId(3L);
	rootUser.setName("root");

	group.addUser(guestUser);
	group.addUser(rootUser);

	SimplePropertyPreFilter filter = new SimplePropertyPreFilter();
	filter.getExcludes().add("name");
	
	System.out.println(JSON.toJSONString(group, filter));
}
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Execution Result:

{"id":0,"users":[{"id":2},{"id":3}]}
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3.3 Use multiple property filters to exclude fields that do not require serialization

If you only want to filter fields in a particular class, you can specify the class object and fields of the corresponding class when creating the filter.

In the following example, create a filter for Group and User to filter out the different fields.

/** * use multiple attribute filters to exclude fields that do not require serialization. */
@Test
public void testExcludeMultiFilter(a) {
	Group group = new Group();
	group.setId(0L);
	group.setName("admin");
	
	User guestUser = new User();
	guestUser.setId(2L);
	guestUser.setName("guest");
	
	User rootUser = new User();
	rootUser.setId(3L);
	rootUser.setName("root");
	
	group.addUser(guestUser);
	group.addUser(rootUser);
	
	// Group filter to filter out the ID field
	SimplePropertyPreFilter filter1 = new SimplePropertyPreFilter(Group.class);
	filter1.getExcludes().add("id");
	// Filter out the name field
	SimplePropertyPreFilter filter2 = new SimplePropertyPreFilter(User.class);
	filter2.getExcludes().add("name");
	
	System.out.println(JSON.toJSONString(group, new SimplePropertyPreFilter[] {filter1, filter2}));
}
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Execution Result:

{"name":"admin","users":[{"id":2},{"id":3}]}
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4. Use a property filter to include the fields you want to serialize.

In some cases, we only need to serialize individual fields, or when there are more fields to exclude than to serialize, we can use include rather than exclude filters.

/** * use property filters to contain fields that need to be serialized. */
@Test
public void testIncludeMultiFilter(a) {
	Group group = new Group();
	group.setId(0L);
	group.setName("admin");
	
	User guestUser = new User();
	guestUser.setId(2L);
	guestUser.setName("guest");
	
	User rootUser = new User();
	rootUser.setId(3L);
	rootUser.setName("root");
	
	group.addUser(guestUser);
	group.addUser(rootUser);
	
	// Group serializes only id and users
	SimplePropertyPreFilter filter1 = new SimplePropertyPreFilter(Group.class, "id"."users");
	// User serializes only name
	SimplePropertyPreFilter filter2 = new SimplePropertyPreFilter(User.class);
	filter2.getIncludes().add("name");
	
	System.out.println(JSON.toJSONString(group, new SimplePropertyPreFilter[] {filter1, filter2}));
}
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Execution Result:

{"id":0,"users":[{"name":"guest"},{"name":"root"}]}
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5. Customize attribute filtering rules

In some special scenarios, the above simple exclusion or inclusion methods cannot meet actual application requirements.

In this case, you can consider using a custom attribute filter to achieve filtering. This implementation is very flexible and can be implemented according to actual requirements.

Some sort of rule judgment can be performed on classes, field names, and field values to determine whether serialization is required.

To implement the apply method in the PropertyFilter interface, return true to indicate that the field is included, and return false to indicate that the field is filtered out.

/ * * *@author wenshao[[email protected]]
 */
public interface PropertyFilter extends SerializeFilter {

    / * * *@paramobject the owner of the property. The object to which the field belongs *@paramname the name of the property. The field name *@paramvalue the value of the property. The field values *@return true if the property will be included, false if to be filtered out
     */
    boolean apply(Object object, String name, Object value);
}
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/** * Custom attribute filtering rules, the most flexible way to achieve field and value filtering. * /
@Test
public void testPropertyFilter(a) {
	Group group = new Group();
	group.setId(0L);
	group.setName("admin");
	
	User guestUser = new User();
	guestUser.setId(2L);
	guestUser.setName("guest");
	
	User rootUser = new User();
	rootUser.setId(3L);
	rootUser.setName("root");
	
	group.addUser(guestUser);
	group.addUser(rootUser);
	
	PropertyFilter filter = new PropertyFilter() {
        @Override
        public boolean apply(Object object, String name, Object value) {
        	//System.out.println(object + " " + name + " " + value);
            if (name.equals("name")) {
                return false; // Exclude the field named name
            }
            if (value.toString().equals("2")) {
            	return false; // Exclude fields with value 2
            }
            return true; // Contains the field or value}}; System.out.println(JSON.toJSONString(group, filter)); }Copy the code

Execution Result:

{"id":0,"users":[{},{"id":3}]}
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